Download Abstracts of research articles focusing on the climate change and

Abstracts of research articles focusing on
the climate change and climate change prediction
studies for the Mediterranean Region published
in refereed journals during 2007 - 2015
Rubin S. Ziv B. PALDOR N. Tropical Plumes over Eastern North Africa as a Source of
Rain in the Middle East MONTHLY WEATHER REVIEW 135, 4135-4148, DOI:10.1175/2007MWR1919.1, 2007
Tropical plumes (TPs) reflect tropical–extratropical interaction associated with the
transport of moisture from the Tropics to extratropical latitudes. They are observed in
satellite images as continuous narrow cloud bands ahead of upper-level subtropical
troughs at times when the subtropical jet is highly perturbed. Rainstorms usually develop
in the exit regions of TPs, so their presence over northern Africa has an impact on the
precipitation regime in the southeastern Mediterranean. Based on satellite images and
rainfall measurements from Israel, 10 TPs over eastern North Africa between 1988 and
2005 in which considerable rain was recorded were selected. Using the NCEP–NCAR
reanalysis data, the structure and evolution of these TPs were characterized and their
regional canonical features were identified. A typical TP that occurred in March 1991 is
described in detail. The main canonical characteristics are as follows: the TP
development is preceded by an incubation period, expressed either as a stationary upperlevel trough, persisting 2–6 days, or as two consecutive TP pulses; the preferred location
for TP origin is 5°–15°N, 5°W–15°E; the TP is separated from the underlying dry
Saharan PBL; the subtropical trough undergoes a phase locking with the lower tropical
trough; the cloudiness in the TP-induced rainstorm is mostly stratified with continuous
moderate rain, originating from midlevel moisture; and the TP tends to be followed by a
midlatitude cyclogenesis over the eastern Mediterranean. This analysis proposes several
explanations for the efficiency of the TPs in transporting moisture over a 2000-km
distance.
S. O. Krichak, P. Alpert, K. Bassat, and P. Kunin The surface climatology of the
eastern Mediterranean region obtained in a three-member ensemble climate change
simulation experiment Adv. Geosci., 12, 67–80, 2007 www.adv-geosci.net/12/67/2007/
Abstract. Two configurations of RegCM3 regional climatemodel (RCM) have been used
to downscale results of two atmosphere-ocean global climate model (AOGCM)
simulations of the current (1961–1990) and future climates (2071– 2100) over the eastern
Mediterranean (EM) region. The RCM domain covering the EM region from northern
Africa to central part of Asia Minor with grid spacing of 50 km was used. Three sets of
RCM simulations were completed. Results of the RCM experiment support earlier
projections of a temperature (annual precipitation) increase (decrease) to the end of 21st
century over the EM. The roles of several major factors in controlling uncertainty of the
climate change estimates are evaluated. The main uncertainty factors appear to be
associated with possible inadequacies in RCM description of the EM-climate-controlling
developments over remotely located areas as well as those in the simulations of the global
climate and its trends by the AOGCMs.
Amir Givati and Daniel Rosenfeld Possible impacts of anthropogenic aerosols on
water resources of the Jordan River and the Sea of Galilee WATER RESOURCES
RESEARCH, VOL. 43, W10419, doi:10.1029/2006WR005771, 2007
Abstract Insights are provided to the hitherto unexplained decreasing trends in the
available water for consumption from the Sea of Galilee and in the outflow of the main
springs of the Jordan River with respect to the nearby rainfall. The loss of available water
of about 110 million m3 yr1 (about 6.5% of the national water consumption in Israel) is
shown to be caused by a decreasing trend in the factor of precipitation enhancement by
uplifting on topographic barriers. Previous studies, reviewed here, show that the most
probable cause of this decreasing trend is an increasing trend in the concentrations of
submicron air pollution particles during the last half century. These particles slow down
the conversion of cloud drops into raindrops and snow flakes, thus decreasing
precipitation from short-lived clouds such as form in moist air that crosses topographic
barriers. This decreasing trend was partially mitigated by cloud seeding for rain
enhancement, but apparently, the air pollution dominated and caused a net loss of
orographic precipitation. A large portion of the water resources in this semiarid part of
the world results from orographic precipitation. Therefore this is an issue with major
economic and societal implications, not only to the study area but to many other densely
populated parts of the world where the livelihood of the inhabitants depends on water
resulting from orographic precipitation, which might be compromised by the air pollution
produced by the very people who depend on that water.
P. Alpert, N. Halfon and Z. Levin, Does air pollution really suppress precipitation in
Israel?, J. Appl. Meteoro. And Climatolo., 47, 4, 933-943, 2008.
Abstract Trends in the orographic rainfall ratio R0 over Israel are reevaluated. It is shown
that the rainfall has not changed significantly over most of the mountainous stations, with
some significant increases over the central mountains. The overall evaluation of R0 for
all potential station pairs, calculating the ratio of each mountain station separately over
each coastal or seashore station, indicates that about 50% of all pairs show a positive
trend in R0. The high spatial variability, especially over the mountains, allows for finding
orographic rainfall ratio trends that are significant in both the positive and negative
directions . The correct definition of R0 in the Israeli case requires the use of a seashore
cluster of stations. If some of the seashore stations are replaced by inland stations, and in
particular stations that are right over the region of maximum positive rainfall urban
enhancement due to the thermal heat island or other urban effects, a seemingly decreasing
“orographic ratio” is unavoidable. In such a case, urban dynamical positive effects on
coastal rainfall can be erroneously interpreted as pollution suppression of orographic
rainfall. When seashore stations are selected as required by a proper definition of the
orographic ratio, increasing R0 is obtained over central Israel and an insignificant trend
over the north is found. Furthermore, evaluation of the ratio of rainfall for the upwind in
comparison with the downwind side of the Galilee Mountains exhibits an increasing
trend, opposite to the recent findings of Givati and Rosenfeld. The rainfall analysis shows
no evidence of any suppression of rainfall over the mountains due to pollution, and at
least in Israel other factors besides aerosols are predominant in defining the trends in the
orographic rainfall ratio
P. Alpert, S.O. Krichak, H. Shafir, D. Haim and I. Osetinsky, Climatic trends to
extremes employing regional modeling and statistical interpretation over the E.
Mediterranean, Global and Planetary Change, 63, 163-170, 2008.
Results of regional climate modeling performed at the International Centre for
Theoretical Physics, Trieste, Italy, are analyzed for the E. Mediterranean region. It is
found that the average temperature over the Mediterranean area has increased by 1.5–
4 °C in the last 100 yr. The temperature in the years 2071-2100 according to the A2 and
B2 scenarios are predicted to increase by about 4 °C and 6 °C respectively over Northern
Israel in comparison with the control run for 1961–1990. The precipitation above most of
the Mediterranean shows a dominant negative trend in the last 50 yr. A large negative
trend in the A2 scenario is found over Northern Israel, while B2 scenario shows no
significant trend. There is a tendency toward extreme events. It is found that the extreme
precipitation over Northern Israel shows significant increasing trends for the A2 and B2
scenarios with respect to the present climate. Also, the standard deviation of the average
annual precipitation is higher in the A2 and B2 scenarios showing a trend toward both
drier as well as wetter years in the future
A. Mariotti, N. Zeng, J. H. Yoon, V. Artale, A. Navarra, P. Alpert and Z. X. Li, Mediterranean
water cycle changes: transition to drier 21st century conditions in observations and CMIP3
simulations, Environmental Research Letters, 3, 044001 (8pp) doi:10.1088/17489326/3/4/044001, 2008.
Abstract We use CMIP3 multi-model simulations to show how individual hydroclimatic
changes will concur to determine even greater alterations of 21st century Mediterranean
water cycle characteristics, with contrasting behavior over land and sea. By 2070–2099,
the average of the models predicts a 20% decrease in land surface water availability and a
24% increase in the loss of fresh water over the Mediterranean Sea due to precipitation
reduction and warming-enhanced evaporation, with a remarkably high consensus among
analyzed models. The projected decrease in river runoff from the surrounding land will
further exacerbate the increase in Mediterranean Sea fresh water deficit. 20th century
simulations indicate that the ‘transition’ toward drier conditions has already started to
occur and has accelerated around the turn of the century towards the larger rates projected
for the 21st century. These tendencies are supported by observational evidence of
century-long negative trends in regionally averaged precipitation, PDSI and discharge
from numerous rivers; and are consistent with reported increases in Mediterranean sea
water salinity.
Akio Kitoh, Akiyo Yatagai and Pinhas Alpert First super-high-resolution model
projection that the ancient “Fertile Crescent” will disappear in this century,
Hydrological Research Letters 2, 1-4 DOI: 10.3178/HRL.2.1, 2008.
Abstract: The first full projections of rainfall and streamflow in the “Fertile Crescent” of
Middle East are presented in this paper. Up until now, this has not been possible due to
the lack of observed data and the lack of atmospheric models with sufficient resolution.
An innovative super-high-resolution (20-km) global climate model is employed, which
accurately reproduces the precipitation and the streamflow of the present-day Fertile
Crescent. It is projected that, by the end of this century, the Fertile Crescent will lose its
current shape and may disappear altogether. The annual discharge of the Euphrates River
will decrease significantly (29-73%), as will the streamflow in the Jordan River. Thus
countermeasures for water shortages will become much more difficult.
Krichak SO, Alpert P, Kunin Projections of climate change over non-boreal east
Europe during first half of twenty-first century according to results of a transient
RCM experiment. In Regional aspects of climate-terrestrial-hydrologic interactions
in non-boreal eastern Europe, [P.Ya. Groisman and S.V. Ivanov, eds], Springer,
NATO Science for Peace and Security Series, Series C: Environmental Security, pp.
55-62. 2009
Abstract. Climate change trends over the southern east-Europe are evaluated according
to results of a climate simulation experiment with the ICTP RegCM3 regional climate
model driven from the lateral boundaries by results of ECHAM5/MPI-OM1 transient
climate simulation from 1960 to 2060 (SRES A1B emission scenario after 2001). The
trends projected include – precipitation: winter and spring – rise over the central eastEurope and drop over the eastern Mediterranean region, summer-autumn – drop over
east-Europe and northern eastern-Mediterranean, rise over the Middle East (especially in
autumn); 2-m air temperature: winter and spring – rise over the whole region with a
maximum over its eastern and north-eastern (especially) and south-eastern parts, summer
– rise with a maximum over the Middle East and minimum over north-eastern part,
autumn – rise with maximum over the Caspian, Black Seas and northern areas of the
European Territory of Russia.
R. Samuels, A. Rimmer and P. Alpert, Effect of Extreme Rainfall Events on the Water Resources
of the Jordan River, Journal of Hydrology, 375, 513-523, doi:10.1016j. hydrol.2009.07.001,
2009.
As a response to climate change, shifting rainfall trends including increased multi-year
droughts and an escalation in extreme rainfall events are expected in the Middle East.
The purpose of this study is to evaluate the potential impact of these shifting trends on
stream flow in the Jordan River and its tributaries. We use a non-homogeneous hidden
Markov model to generate artificial daily rainfall simulations which capture
independently shifting trends of increased droughts and escalated extreme. These
simulations are then used as input into a hydrological model calibrated for the upper
catchments of the Jordan River to compare the impact on stream flow and water
resources between the different rainfall scenarios. We compare the predicted baseflow
and surface flow components of the tested watersheds, and find that while an increase in
extreme rainfall events increases the intensity and frequency of surface flow, the over all
flow to the Jordan River, and the characteristics of the baseflow in the Jordan River
system is not largely impacted. In addition, though it has been suggested that in the case
of a multi-year drought the karstic nature of the aquifer might lead to more intense, nonlinear reductions in stream flow, here we quantify and show the conditions when annual
stream flow reduce linearly with rainfall, and when these relations will become nonlinear.
Simon O. Krichak Pinhas Alpert Pavel Kunin Numerical simulation of seasonal
distribution of precipitation over the eastern Mediterranean with a RCM Clim Dyn
DOI 10.1007/s00382-009-0649-x, 2009
Abstract Regional climate model (RCM) RegCM3 with 50 km horizontal resolution
driven from the lateral boundaries by the data from NCEP/NCAR re-analysis is used in a
series of ten climate downscaling experiments over the eastern Mediterranean (EM)
region. Results of the experiments are characterized by seasonal precipitation patterns
with notable offshore precipitation zones positioned 50 km westward of a less intense
precipitation zone over the coastal area. Atmospheric processes determining the
distribution of seasonal precipitation patterns in the EM are analyzed based on results of
the RCM experiments performed. Level of success of the model representation of the
actual precipitation over the ECM appears to be depending on that of precipitation
balance over different parts of the domain. Excessive moisture convergence over a subarea usually takes place at the expense of moisture divergence from neighboring areas.
Synoptic mechanism causing formation of the precipitation zone in the offshore zone
appears to be associated with the role of meridionally oriented atmospheric trough
systems extending from Scandinavia or Siberia to the EM during the period with rainy
events. In such situations, air flows with strong northern components lead to intense
transport of cold air masses to the EM. Meeting of the cold air masses the warm and
humid air over the sea surface in the offshore zone causes formation of persistent squall
lines and heavy rains there. Such processes may continue quite long as long as the
troughs are stationary.
Y. Yosef, H. Saaroni and P. Alpert, Trends in daily rainfall Intensity over Israel
1950/1-2003/4, The Open Atmospheric Science Journal, 3, 196-203, 2009
Abstract: The study focuses on long-term trends of daily rainfall in Israel as a function of
their intensity in order to identify potential trends in rainfall extremity. The study period
is the rainy season, October-May between 1950/1 and 2003/4. For the total rainfall, an
increased trend is shown across Israel, especially for the central and southern regions,
though non-significant. Daily rainfall intensity showed non-significant trends of increase
in the heavy rainfall at the center and south and decrease at the north. The light to
moderate rainfall trends increased in the north while they decreased at the center and
south. Trends are significantly correlated with known teleconnection patterns, especially
the East Atlantic- Western Russia and the North Sea-Caspian Sea patterns. Positive
trends toward heavier rainfall are noted in Israel, which are significant in several specific
locations. This finding has to be carefully followed since the region is a climatic border
subjected to severe water shortage and is predicted to dry-up in most global warming
scenarios.
N. Halfon, Z. Levin and P. Alpert, Temporal rainfall fluctuations in Israel and their
possible link to urban and air pollution effects, Environ. Res. Lett. 4, (12pp),
doi:10.1088/1748-9326/4/2/025001, 2009.
Abstract In this paper we analyze spatial variations of the annual rainfall that have taken
place in the non-arid regions of Israel (annual rainfall >200 mm) during the years 1952–
2006, incorporating all available data. The results of the present study over the research
area as a whole indicate that no significant temporal change of the annual rainfall
occurred in any region of the study area. However, focusing on spatial rainfall
fluctuations between sub-regions in the study area, a significant increase was observed
between the stations located downwind and those upwind of the Greater Tel Aviv region.
This increase supports previous reports showing that rainfall enhancement is observed
downwind (and close) to urban centers. In contrast to a few previous reports, no decrease
in the ratio between the mountain precipitation to that over the coastal region was found.
Over the period of the present study, the rainfall ratio between the upwind slopes and the
seashore remained unchanged, with a slight increase in the central part of the country.
The only hilly place where a slight decrease in annual rainfall was observed is the lee side
(eastern slopes) of the Galilee Mountains. This result is important because the eastern
slopes of the Galilee Mountains have for years been part of the target area for Israeli
artificial cloud seeding for rain enhancement. The results therefore suggest that unless
there was a pronounced change in the synoptic conditions during rain spells, seeding in
Israel had no positive effect on rainfall amounts
Samuels R, Rimmer A, Hartman, A., Krichak SO, Alpert P Climate Change
impacts on the Jordan River, Israel: Downscaling application from a Regional
Climate Model, J. Hydrometeorology, 11, 860-879, 2010,
Abstract. The integration of climate change projections into hydrological and other
response models used for water resource planning and management is challenging given
the varying spatial resolutions of the different models. In general, climate models are
generated at spatial ranges of hundreds of kilometers, while hydrological models are
generally watershed specific and based on input at the station or local level. This paper
focuses on techniques applied to downscale large-scale climate model simulations to the
spatial scale required by local response models (hydrological, agricultural, soil).
Specifically, results were extracted from a regional climate model (RegCM) simulation
focused on the Middle East, which was downscaled to a scale appropriate for input into a
local watershed model [the Hydrological Model for Karst Environment (HYMKE)]
calibrated for the upper Jordan River catchment. With this application, the authors
evaluated the effect of future climate change on the amount and form of precipitation
(rain or snow) and its effect on streamflow in the Jordan River and its tributaries—the
major water resources in the region. They found that the expected changes in the form of
precipitation are nearly insignificant in terms of changing the timing of streamflow.
Additionally, the results suggest a future increase in evaporation and decrease in average
annual rainfall, supporting expected changes based on global models in this region.
Debbie Hemming, Carlo Buontempo, Eleanor Burke, Mat Collins and Neil Kaye
How uncertain are climate model projections ofwater availability indicators across
the Middle East? Phil. Trans. R. Soc. A 2010 368, doi: 10.1098/rsta.2010.0174,2010.
The projection of robust regional climate changes over the next 50 years presents a
considerable challenge for the current generation of climate models. Water cycle changes
are particularly difficult to model in this area because major uncertainties exist in the
representation of processes such as large-scale and convective rainfall and their feedback
with surface conditions. We present climate model projections and uncertainties in water
availability indicators (precipitation, run-off and drought index) for the 1961–1990 and
2021–2050 periods. Ensembles from two global climate models (GCMs) and one
regional climate model (RCM) are used to examine different elements of uncertainty.
Although all three ensembles capture the general distribution of observed annual
precipitation across the Middle East, the RCM is consistently wetter than observations,
especially over the mountainous areas. All future projections show decreasing
precipitation (ensemble median between −5 and −25%) in coastal Turkey and parts of
Lebanon, Syria and Israel and consistent run-off and drought index changes. The
Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4)
GCM ensemble exhibits drying across the north of the region, whereas the Met Office
Hadley Centre work Quantifying Uncertainties in Model Projections—Atmospheric
(QUMP-A) GCM and RCM ensembles show slight drying in the north and significant
wetting in the south. RCM projections also show greater sensitivity (both wetter and
drier) and a wider uncertainty range than QUMP-A. The nature of these uncertainties
suggests that both large-scale circulation patterns, which influence region-wide
drying/wetting patterns, and regional-scale processes, which affect localized water
availability, are important sources of uncertainty in these projections. To reduce large
uncertainties in water availability projections, it is suggested that efforts would be well
placed to focus on the understanding and modelling of both large-scale processes and
their teleconnections with Middle East climate and localized processes involved in
orographic precipitation.
F. Jin, J., A. Kitoh and P. Alpert, Water cycle changes over the Mediterranean: a
comparison study of a super-high-resolution global model with CMIP3. Phil. Trans.
Roy. Soc. A., 368, 1-13, 2010.
Water cycle components over the Mediterranean for both a current run (1979–2007)
and a future run (2075–2099) are studied with the Japan Meteorological Agency’s 20
km grid global climate model. Results are compared with another study using the
Coupled Model Intercomparison Project Phase 3 ensemble model (hereafter, the
Mariotti model). Our results are surprisingly close to Mariotti’s. The projected mean
annual change rates of precipitation (P) between the future and the current run for sea
and land are − 11 per cent and −10 per cent, respectively, which are not as high as
Mariotti’s. Projected changes for evaporation (E) are+9.3 per cent and−3.6 per cent,
compared with +7.2 per cent and −8.1 per cent in Mariotti’s study, respectively.
However, no significant difference in the change in P–E over the sea body was found
between these two studies. The increased E over the eastern Mediterranean was found
to be higher than that in the western Mediterranean, but the P decrease was lower.
The net moisture budget, P-E , shows that the eastern Mediterranean will become
even drier than the western Mediterranean. The river model suggests decreasing water
inflow to the Mediterranean of approximately 36 per cent (excluding the Nile)
H. Saaroni, N. Halfon, B. Ziv, P. Alpert and H. Kutiel, Links between the rainfall regime in Israel
and location and intensity of Cyprus Lows, Int. J. Climatol., 30, 1014-1025, DOI:
10.1002/joc.1912, 2010.
ABSTRACT: The interannual variations and the spatial distribution of rainfall in the
Mediterranean and semi-arid regions of Israel are analysed with respect to variations in the
occurrence e of the typical synoptic systems of the Eastern Mediterranean. The synoptic
analysis is based on a daily, semi-objective synoptic classification. The study covers the
months November – March, in which 90% of the annual rainfall is obtained, mostly resulting
from Cyprus lows. The interannual variations of the rainfall are well explained by the
synoptic types, and the occurrences of Cyprus lows are highly correlated with the rainfall. It
was found that the daily and seasonal rainfall are highly dependent on the depth of the
cyclone. Moreover, deep lows are more effective for the mountainous regions, due both to
the enhanced orographic effect and to the fact that stronger winds, associated with deep lows,
are more efficient in transporting rain-producing clouds from the Mediterranean Sea inland.
The location of the cyclone determines the spatial distribution of the rain it produces over
Israel. The cyclones located east of Cyprus were found productive mainly for the southern
parts of the study region, while those located to the west and north of Israel were found
productive for the north of the country. The high sensitivity of the rainfall to the location of
the surface cyclones emphasizes the major role that lower level moisture transport plays in
rain formation.
S. O. Krichak & J. S. Breitgand & R. Samuels & P. AlpertA double-resolution
transient RCM climate change simulation experiment for near-coastal eastern zone
of the Eastern Mediterranean region, Theor Appl Climatol
10.1007/s00704-010-0279-6, 2011
103:167–195, DOI
Abstract A double-resolution regional experiment on hydrodynamic simulation of climate
over the eastern Mediterranean (EM) region was performed using an International Center
for Theoretical Physics, Trieste RegCM3 model. The RegCM3 was driven from the
lateral boundaries by the data from the ECHAM5/MPI-OM global climate simulation
performed at the MPI-M, Hamburg and based on the A1B IPCC scenario of greenhouse
gases emission. Two simulation runs for the time period 1960-2060, employing spatial
resolutions of 50 km/ 14 L and 25 km/18 L, are realized. Time variations of the
differences in the space distributions of simulated climate parameters are analyzed to
evaluate the role of smaller scale effects. Both least-square linear and non-linear trends of
several characteristics of the EM climate are evaluated in the study. One of the key
findings with regard to linear trends is a notable and statistically significant precipitation
drop over the near coastal EM zone during December-February and SeptemberNovember. Statistically significant positive air temperature trends are projected over the
entire EM region during the four seasons. Also projected are increases in air temperature
extremes and the relative contribution of convective processes in the Southern
Mediterranean coastal zone (ECM) region. A notable sensitivity of projected larger-scale
climate change signals to smaller-scale effects is also demonstrated.
Smiatek, G. ; Kunstmann, H. ; Heckl, A. High‐resolution climate change simulations
for the Jordan River area, Journal of Geophysical Research: Atmospheres,
Vol.116(D16), 2156-2202 ; DOI: 10.1029/2010JD015313 , 2011
Abstract: For the estimation of future climate conditions in the Jordan River region, the
National Center for Atmospheric Research–Penn State University meteorology model in
the versions 3.5 and 3.7 driven with boundary data from the Max‐Planck‐Institute for
Meteorology and Hadley Centre global circulation models and the Special Report on
Emission Scenarios A1B emission scenario has been used. The spatial resolution of the
nested dynamic downscaling approach was 18.6 km, and the transient runs were
performed for the period 1960–2099. The investigated statistics include mean
precipitation, frequency and intensity of wet days and strong precipitation events, as well
as mean temperature and heat wave duration index. The results show that the models
satisfactorily reproduce the mean temperature and precipitation patterns. The comparison
with the observational reference for the period 1961–1990 reveals a bias in the annual
mean precipitation ranging from −20% to +17%, with an ensemble mean of −3%. The
models show limitations in reproducing the precipitation seasonality. All models
underestimate the wet day frequency and show differences in the strong precipitation
events. The simulations of the future climate signal indicate an ensemble mean increase
of the annual mean temperature of approximately 2.1 K in the period 2031–2060 and 3.7
K for the period 2070–2099 related to the 1961–1991 mean. In the same periods, the
annual mean precipitation is simulated to decrease by approximately −11.5% and −20%,
respectively, which means a reduction of expected water availability in the Jordan River
region. All models show an increase of the heat wave duration index. A significant
elevation dependence is present in the simulated future climate signal on both
temperature and precipitation. The simulations show an increased coefficient of variation
in annual precipitation, indicating that larger interannual precipitation variability can be
expected in the future. Significant reduction of expected water availability in the Jordan
River region Significant elevation signal present in the simulated future climate Increased
coefficient of variation in simulated future annual precipitation
Shohami, David ; Dayan, Uri ; Morin, Efrat Warming and drying of the eastern
Mediterranean: Additional evidence from trend analysis Journal of Geophysical
Research. Atmospheres, 116(22) DOI: 10.1029/2011JD016004, 2011
Abstract: Trends in atmospheric variables over EM indicate warmer and drier
conditions Significant warming was found in surface station summer temperature data
Precipitation trends are negative but insignificant due to high natural variance The
climate of the eastern Mediterranean (EM), at the transition zone between the
Mediterranean climate and the semi-arid/arid climate, has been studied for a 39-year
period to determine whether climate changes have taken place. A thorough trend analysis
using the nonparametric Mann-Kendall test with Sen's slope estimator has been applied
to ground station measurements, atmospheric reanalysis data, synoptic classification data
and global data sets for the years 1964-2003. In addition, changes in atmospheric regional
patterns between the first and last twenty years were determined by visual comparisons of
their composite mean. The main findings of the analysis are: 1) changes of atmospheric
conditions during summer and the transitional seasons (mainly autumn) support a warmer
climate over the EM and this change is already statistically evident in surface
temperatures having exhibited positive trends of 0.21°C/decade; 2) changes of
atmospheric conditions during winter and the transitional seasons support drier conditions
due to reduction in cyclogenesis and specific humidity over the EM, but this change is
not yet statistically evident in surface station rain data, presumably because of the high
natural precipitation variance masking such a change. The overall conclusion of this
study is that the EM region is under climate change leading to warmer and drier
conditions.
Rimmer, A; Givati, A; Samuels, R; Alpert, P Using ensemble of climate models to
evaluate future water and solutes budgets in Lake Kinneret, Israel Journal of
Hydrology, Vol.410(3-4), pp.248-259, DOI: 10.1016/j.jhydrol.2011.09.025, 2011
Abstract: Identifying and quantifying future climate effects on water resources has major
economic and societal implications, rendering such studies extremely important for water
planners. Here we integrate output from one high resolution global (Japan Meteorological
Agency) and three regional (ECHAM-RegCM, Hadley-MM5, ECHAM-MM5) climate
models into three hydrological tools (1. annual incoming water volumes; 2. evaporation
from the lake; and 3. lake salinity) to provide first approximations of climate change
impacts on water quantity and quality in Lake Kinneret (also known as Sea of Galilee),
the major freshwater resource in Israel. Meteorological data extracted from the climate
models were used as input data into the models. Results were calculated for the historical
1979–2009 and the future 2015–2060 periods. The modeled historical period was verified
against observed data, first by each model alone, and then by the combined model
structure. Predicted results varied between the climate models. The ECHAM-RegCM
predicted decreased precipitation in an average rate of 7 mm year1 (0.8% annually) while
the trends of precipitation predicted by the other models were less obvious. According to
the combination of ECHAM-RegCM, ECHAM-MM5 and Hadley-MM5 with the lake
evaporation model, the evaporation will increase by 0.2–0.6 Mm3 (0.10–0.25%) annually
while according to the JMA no trend was found. The lake salinity is mostly impacted by
changes in inflows and therefore only the ECHAM-RegCM predicted significant increase
of salinity (from 280 ppm Cl today to 450 ppm Cl in 2060), while the trends of salinity
according to other models were mild.
R. Samuels, G. Smiatek, S. Krichak, H. Kunstmann, P. Alpert, Extreme Value
Indicators in highly resolved Climate Change Simulations for the Jordan River
Area. J. Geoph. Res., 116, D24123, 9 pp., doi:10.1029/2011JD016322, 2011
Abstract. Understanding and predicting changing trends and frequency of extreme
rainfall and temperature events are extremely important for optimal planning in many
sectors including agriculture, water resource management, health and even economics.
For people living in the Jordan River region of the Middle East such changes can have
immediate devastating impacts as water resources are already scarce and over-exploited
and summer temperatures in the desert regions can reach 45 degrees or higher.
Understanding and forecasting shifts in frequency and intensity of extreme events can
provide crucial information for planning and adaptation. In this paper we present results
from regional climate model simulations with RegCM3 and MM5 centered on the
Eastern Mediterranean region. Our analysis focusses on changes in extreme temperature
and rainfall events. We show that maximum daily summer temperature is expected to
increase by between 2.5-3◦16 C with an increase in warm spell length. Precipitation
extremes are expected to increase with longer dry spells, shorter wet spells and increases
in heavy rainfall. Model agreement for the control period 1961-1990 is higher in the
southern region than in the north, perhaps due to the complex topography suggesting that
even small differences in spatial scale play an important role. In addition, we notice that
the chosen global model plays an important role in determining future temperature trends
while the choice of regional climate model is critical for understanding how precipitation
is expected to evolve.
Z. Levin, N. Halfon and P. Alpert, Reply to comment by Ben-Zvi, A., D. Rosenfeld
and A. Givati on the paper-Levin, Z., N. Halfon and P. Alpert, Reassessment of rain
experiments and operations in Israel including synoptic considerations, Atmos. Res.
97, 513-525. DOI 10.1016 J. Atmosres.2010.06.011, Atm. Res., 99, 593-596, 2011.
Abstract: Levin et al. (2010 ; hereafter LHA) (Levin, Z., Halfon, N., Alpert, P., 2010.
Reassessment of rain experiments and operations in Israel including synoptic
considerations. Atmos. Res. 97, 513–525. DOI:10.1016/j.atmosres.2010.06.011.),
reanalyzed the results of the operational seeding in northern Israel between 1975 and
2007 and the preceding Israel 2 cloud seeding experiment (1969–1975) and concluded
that there is no net increase in precipitation over the target areas. Our analysis revealed
that a synoptic bias during Israel 2 is one of the reasons for the apparent positive effect of
seeding in the northern target area and the negative effect in the southern area both of
which disappeared in the following experiment in the south (Israel 3; 1975–1995) and the
operational seeding in the north. Ben-Zvi et al. (2010 ;hereafter BRG) criticized our
paper primarily on the ground that we did not consider the positive results of Israel 1
experiment (1960–1967). It should be noted that in Israel 1 different seeding lines were
used from those in both Israel 2 and the operational period. In addition, its raw data is not
accessible anymore for reanalysis. Furthermore, Israel 2 had been designed as a
confirmatory cross-over experiment to Israel 1 and failed to reproduce its promising
results with double ratio (DR) of ~1.00, namely, zero rainfall enhancements. The same
DR values were also found in Israel 3 and in the operational seeding. Therefore, because
of the differences in the two experiments, the lack of access to the raw data and the
disappointing results of the confirmatory experiment, we decided to concentrate our
analysis on the more recent seeding activities. The attempt by BRG to explain the
reduction of the DR to ~1.00 in the operational seeding period by the suppression due to
pollution have been disproved by Alpert et al. (2008, 2009) and also fail to explain the
sharp decline of the target/control ratio right at the beginning of the operational seeding
period when the lucky draw in this area came to its end (see LHA).
F. Jin,, A. Kitoh, and P. Alpert, Climatological relationships among the moisture
budget components and rainfall amounts over the Mediterranean based on a superhigh-resolution climate model, J. Geophys. Res., 116, D09102,
doi:10.1029/2010JD014021, 2011.
Moisture budget components over a rectangular region defined by the
longitudes 6.0°W–36.0°E and latitudes 30.0°N to 45.0°N, with an area of about
6.08 × 106 km2 over the Mediterranean (Med) Basin, are studied by the use of
the Japan Meteorological Agency super ‐ high‐ resolution (20 km) GCM
monthly mean data. The research time periods are 1979–2007 for current run
and 2075– 2099 for future run. Six rainy months of October to March with a
total of 168 months for the current run and 144 months for the future run were
selected. The rain months have been categorized into five groups of months
based on the mean monthly rainfall amounts where the five groups are P < 1.0,
1.0≤P < 1.5, 1.5≤P < 2.0, 2.0≤P < 2.5, and 2.5 mm/d ≤ P. We found that
generally, over the Mediterranean, the outflow‐ inflow is balancing the
independently calculated evaporation ‐ precipitation quite well with a
correlation coefficient of about 0.89. The present seasonal (October‐March)
precipitation simulated from the 20 km GCM showed a quite reasonable
agreement with the CRU. The seasonal area mean precipitation and evaporation
are 1.85 mm/d and 2.44 mm/d, respectively. The largest two precipitation
categories contribute over 50% of the total seasonal rainfall. The evaporation
varies positively with the precipitation for all precipitation categories. Also, the
relatively high mean recycling ratio (55%) indicates that the local Med
evaporation has a central role in the local precipitation. Another important
finding is that the decreasing trend of recycling ratio with the rising of the
precipitation category implies that the outside moisture inflow role increases
with the increase of the precipitation category. For all the precipitation
categories, the total outflow is larger than the total inflow, indicating that the
Med area is an important source of moisture. Individual boundary moisture flux
shows that the main moisture comes from the west boundary and contributes
59% of the total inflow, while the main outflow is through east boundary and is
responsible for 46% of total outflow. Analysis of monthly precipitation
indicates that the October and November have the two largest amount of
precipitation over the research region. The moisture budget study separated for
the east and the west Med shows that the area mean precipitation for the east
and the west Med are 2.14 and 2.29 mm/d, while the evaporation are 4.48 and
3.59 mm/d. The plausible reason for the differences between these two basins
has been discussed. The moisture supplies to the east Med is mainly from the
west boundary, while for the west Mediterranean, the north boundary inflow
also plays an important role along with the west boundary. The future moisture
budget components over Med suggest that the precipitation is decreasing from
1.85 to 1.62 mm/d and the evaporation is increasing from 2.44 to 2.56 mm/d
between current and future. Another finding is that the largest precipitation
number of months decreases from 12% to only 6% of the total number of
months, while the intensity of the precipitation in this category enhances in the
future
Wanli Wu, Yubao Liu, Ming Ge, Dorita Rostkier-Edelstein, Gael Descombes, Pavel
Kunin, Thomas Warner, Scott Swerdlin, Amir Givati, Thomas Hopson, David Yates
Statistical downscaling of climate forecast system seasonal predictions for the
Southeastern Mediterranean, Atmospheric Research 118, 346–356, 2012
Abstract Most of the annual rainfall in the Southeastern Mediterranean falls in the wet
season from November to March. It is associated with Mediterranean cyclones, and is
sensitive to climate variability. Predicting the wet season precipitation with a few months
advance is highly valuable for water resource planning and climate-associated risk
management in this semi-arid region. The regional water resource managements and
climate-sensitive economic activities have relied on seasonal forecasts from global
climate prediction centers. However due to their coarse resolutions, global seasonal
forecasts lack regional and local scale information required by regional and local water
resource managements. In this study, an analog statistical-downscaling algorithm, knearest neighbors (KNN), was introduced to bridge the gap between the coarse forecasts
from global models and the needed fine-scale information for the Southeastern
Mediterranean. The algorithm, driven by the NCEP Climate Forecast System (CFS)
operational forecast and the NCEP/DOE reanalysis, provides monthly precipitations at 2–
4 months of lead-time at 18 stations within the major regional hydrological basins. Largescale predictors for KNN were objectively determined by the correlations between the
station historic daily precipitation and variables in reanalysis and CFS reforecast. Besides
a single deterministic forecast, this study constructed sixty ensemble members for
probabilistic estimates. The KNN algorithm demonstrated its robustness when validated
with NCEP/DOE reanalysis from 1981 to 2009 as hindcasts before applied to downscale
CFS forecasts. The downscaled predictions show fine-scale information, such as stationto-station variability. The verification against observations shows improved skills of this
downscaling utility relative to the CFS model. The KNN-based downscaling system has
been in operation for the Israel Water Authority predicting precipitation and driving
hydrologic models estimating river flow and aquifer charge for water supply.
Kelley, C., M. Ting, R. Seager, and Y. Kushnir, Mediterranean precipitation
climatology, seasonal cycle, and trend as simulated by CMIP5, Geophys. Res. Lett.,
39, L21703, doi:10.1029/2012GL053416, 2012
Winter and summer Mediterranean precipitation climatology and trends since 1950 as
simulated by the newest generation of global climate models, the Coupled Model
Intercomparison Project phase 5 (CMIP5), are evaluated with respect to observations and
the previous generation of models (CMIP3) used in the Intergovernmental Panel on
Climate Change Fourth Assessment Report. Observed precipitation in the Mediterranean
region is defined by wet winters and drier summers, and is characterized by substantial
spatial and temporal variability. The observed drying trend since 1950 was predominantly
due to winter drying, with very little contribution from the summer. However, in the
CMIP5 multimodel mean, the precipitation trend since 1950 is evenly divided throughout
the seasonal cycle. This may indicate that in observation, multidecadal internal
variability, particularly that associated with the North Atlantic Oscillation (NAO),
dominates the wintertime trend. An estimate of the observed externally forced trend
shows that winter drying dominates in observations but the spatial patterns are grossly
similar to the multimodel mean trend. The similarity is particularly robust in the eastern
Mediterranean region, indicating a radiatively forced component being stronger there.
Results of this study also reveal modest improvement for the CMIP5 multi-model
ensemble in representation of the observed six month winter and summer climatology.
The results of this study are important for assessment of model predictions of
hydroclimate change in the Mediterranean region, often referred to as a “hotspot” of
future subtropical drying.
Rana Samuels, Maayan Harel, Pinhas Alpert , A new methodology for weighting
high-resolution model simulations to project future rainfall in the Middle EastClim
Res. Vol. 57: 51–60, doi: 10.3354/cr01147, 2013
ABSTRACT: A divergence metric was used to combine 4 high-resolution climate models
to generate more reliable simulations of future rainfall. The approach is based on the
assumption that the use of multiple models (an ensemble) is superior to the use of a single
model, even if one of the models is shown to better capture past trends. Such an approach
is especially useful in areas with steep climatic gradients, where large-scale climate
models are not effective in capturing orographic and local effects. We applied the
methodology to the Middle East, and specifically to Israel, where climate shifts from arid
to humid temperate occur over a distance of around 400 km. Model weights were
determined by calculating the similarity between the probability distributions of the
models and those of the historical data using the Jenson-Shannon divergence metric.
These weights were then applied to future model projections. Annual amounts of rainfall,
numbers of wet days and numbers of 3 d wet spells were analyzed. Compared with
observed data, the weighted ensemble outperformed the equal weights ensemble, which
outperformed the best model. For the northern and central stations, average annual
amounts of rainfall decreased in both near- and far-future periods, with most of the
change occurring at the peak and in the left-hand tail and less change in the right-hand
tail of the probability distribution. This, combined with the change in the right-hand tail
of the distribution in numbers of wet spells in the near future, suggests that the decline in
overall rainfall will be higher than the corresponding decline in extreme events; or in
other words even though there will be less rainfall, the extreme events will remain, and
even possibly increase. In the south, a mixed trend of slightly increasing median amounts
of rainfall and slightly decreasing extreme events is projected.
Amir Givati, Daniel Rosenfeld The Arctic Oscillation, climate change and the effects
on precipitation in Israel Atmospheric Research 132–133
114–124,
http://dx.doi.org/10.1016/j.atmosres.2013.05.001, 2013
The Arctic Oscillation (AO) has been found in previous studies to be a major synoptic
factor affecting the climate of many regions in the high and mid-latitudes. This paper
demonstrates the physical process by which the AO affects the climate of the Eastern
Mediterranean basin, with a focus on precipitation in Israel as a case study. It is shown
that a trend of increasing AO is associated with a substantial decrease of winter
precipitation from the Iberian Peninsula, though Italy, Greece, Turkey and Cyprus, as
well as Lebanon, Syria and also the northern parts of Israel. Winter rain is slightly
increased in the southern coast of the eastern half of the Mediterranean Sea. The
immediate meteorological causes are shown to be a larger northerly component of the
flow over the Mediterranean Sea, associated with a decreasing relative humidity and
stability, except over the southern coast, where the air mass has the longest track over the
relatively warm water. We suggest here that the observed changes in air flow that drives
the precipitation trends can be explained by shifts in the AO that can be partially
explained by increasing greenhouses gases. Results from the IPCC multi climate models
show that the AO will continue to increase during the 21st century. This increase may
lead to a continuation of the trends discussed here. The importance of the analysis
provided here is in pointing out the possibility that processes that have been predicted by
global warming and changes in global circulation have already started to affect
precipitation and major water resources in the Mediterranean basin.
D. Rostkier-Edelstein, Y. Liu, W. Wu, P. Kunin, A. Givati and M. Ge Towards a
high-resolution climatography of seasonal precipitation over Israel Int. J. Climatol.
DOI: 10.1002/joc.3814, 2013
ABSTRACT: This study demonstrates the capability of the Weather Research and
Forecasting (WRF) model with four dimensional data assimilation (WRF-FDDA) to
produce a high-resolution climatography of seasonal precipitation over Israel and the
surrounding areas. The system was used to dynamically downscale global Climate
Forecast System (CFS) reanalysis with continuous assimilation of conventional and
unconventional observations. Precipitation seasons (December- January-February) in 7
years, including two extreme dry and wet seasons observed in the past decades, were
generated at 2-km spatial resolution. Verification against rain-gauge observations shows
that the WRF-FDDA system effectively reproduces the spatial and inter-annual
variability, as well as the timing, intensity, and length of wet and dry spells. The best
agreement between model and observations was obtained at areas dominated by complex
terrain, illustrating the benefit of the high-resolution lower boundary forcing in the
dynamical downscaling process. In contrast, some biases were observed over coastal-flat
terrain. The model was able to reproduce some of the extreme events, but exhibited
limitations in the case of rare events. This specific discrepancy between the model and
observations suggests that further fine tuning and different model configurations may be
needed to correctly simulate extreme events. The use of an objective weather regimes
verification procedure reveals the skill of the climatography for different types of extratropical cyclones: while biases are larger at coastal-flat areas under shallow-cyclonic
conditions, deep-cyclonic conditions lead to more significant biases in complex terrain
regions. The weather-regimes dependent information may be used for further calibration
of the downscaled precipitation.
Baruch Ziv • Hadas Saaroni • Roee Pargament • Tzvi Harpaz • Pinhas Alpert
Trends in rainfall regime over Israel, 1975–2010, and their relationship to largescale variability Reg Environ Change DOI 10.1007/s10113-013-0414-x, 2013.
Abstract Variations and trends in the rain regime of Israel are analyzed for 1975–2010,
when persistent global warming has been observed. Negative trend is observed over the
majority of Israel, statistically significant only in the super-arid region. The decrease is
significant over the majority of Israel only in the spring, reflecting a shortening of the
rainy season, [3 days/decade. The dry spells are becoming longer, significantly in most of
the stations. The factors affecting these variations, synoptic systems, largescale
oscillations and global temperature, were studied for extended period, 1953–2010. A
simple multiple stepwise regression model applied for the inter-annual rainfall variations
indicates that the occurrence of Cyprus lows is the dominant factor and the
Mediterranean oscillation index, MOI2, is also a significant factor. In order to reduce the
inter-annual noise and reveal inter-decadal variations, the time-series of the rainfall and
its potential predictors were smoothed by 11-year window, showing an increase toward
the 1990s, followed by a decrease, at a higher rate, onward. Correspondingly, the aridity
lines propagated southward till the mid-1990s and then withdrew back, at a larger rate.
The large-scale oscillations and the global temperature explain 83 % of the variance on
the interdecadal time-scale, half of it explained by the global temperature alone. The
findings of this study support the expected poleward expansion of the Hadley cell due to
global warming.
T. Tornros and L. Menzel, Addressing drought conditions under current and future
climates in the Jordan River region Hydrol. Earth Syst. Sci., 18, 305–318,
www.hydrol-earth-syst-sci.net/18/305/2014/ doi:10.5194/hess-18-305-2014, 2014
Abstract. The Standardized Precipitation–Evaporation Index (SPEI) was applied in order
to address the drought conditions under current and future climates in the Jordan River
region located in the southeastern Mediterranean area. In the first step, the SPEI was
derived from spatially interpolated monthly precipitation and temperature data at multiple
timescales: accumulated precipitation and monthly mean temperature were considered
over a number of timescales – for example 1, 3, and 6 months. To investigate the
performance of the drought index, correlation analyses were conducted with simulated
soil moisture and the Normalized Difference Vegetation Index (NDVI) obtained from
remote sensing. A comparison with the Standardized Precipitation Index (SPI), i.e., a
drought index that does not incorporate temperature, was also conducted. The results
show that the 6- month SPEI has the highest correlation with simulated soil moisture and
best explains the interannual variation of the monthly NDVI. Hence, a timescale of 6
months is the most appropriate when addressing vegetation growth in the semiarid
region. In the second step, the 6-month SPEI was derived from three climate projections
based on the Intergovernmental Panel on Climate Change emission scenario A1B. When
comparing the period 2031–2060 with 1961–1990, it is shown that the percentage of time
with moderate, severe and extreme drought conditions is projected to increase strongly.
To address the impact of drought on the agricultural sector, the irrigation water demand
during certain drought years was thereafter simulated with a hydrological model on a
spatial resolution of 1 km. A large increase in the demand for irrigation water was
simulated, showing that the agricultural sector is expected to become even more
vulnerable to drought in the future.
Barıs¸ Onol, Deniz Bozkurt , Ufuk Utku Turuncoglu, Omer Lutfi Sen, H. Nuzhet
Dalfes. Evaluation of the twenty-first century RCM simulations driven by multiple
GCMs over the Eastern Mediterranean–Black Sea region Clim Dyn 42:1949–1965
DOI 10.1007/s00382-013-1966-7, 2014
Abstract In this study, human-induced climate change over the Eastern Mediterranean–
Black Sea region has been analyzed for the twenty-first century by performing regional
climate model simulations forced with large-scale fields from three different global
circulation models (GCMs). Climate projections have been produced with Special Report
on Emissions Scenarios A2, A1FI and B1 scenarios, which provide greater diversity in
climate information for future period. The gradual increases for temperature are widely
apparent during the twenty-first century for each scenario simulation, but ECHAM5driven simulation generally has a weaker signal for all seasons compared to CCSM3
simulations except for the Fertile Crescent. The contrast in future temperature change
between the winter and summer seasons is very strong for CCSM3-A2-driven and
HadCM3-A2-driven simulations over Carpathians and Balkans, 4–5 _C. In addition,
winter runoff over mountainous region of Turkey, which feeds many river systems
including the Euphrates and Tigris, increases in second half of the century since the
snowmelt process accelerates where the elevation is higher than 1,500 m. Moreover,
analysis of daily temperature outputs reveals that the gradual decrease in daily minimum
temperature variability for January during the twenty-first century is apparent over
Carpathians and Balkans. Analysis of daily precipitation extremes shows that positive
trend is clear during the last two decades of the twenty-first century over Carpathians for
both CCSM3-driven and ECHAM5-driven simulations. Multiple-GCM driven regional
climate simulations contribute to the quantification of the range of climate change over a
region by performing detailed comparisons between the simulations.
GERHARD SMIATEK HARALD KUNSTMANN ANDREAS HECKL HighResolution Climate Change Impact Analysis on Expected Future Water Availability
in the Upper Jordan Catchment and the Middle East, JOURNAL OF
HYDROMETEOROLOGY, 15, 1517-1531, DOI: 10.1175/JHM-D-13-0153.1, 2014.
ABSTRACT The impact of climate change on the future water availability of the upper
Jordan River (UJR) and its tributaries Dan, Snir, and Hermon located in the eastern
Mediterranean is evaluated by a highly resolved distributed approach with the fifthgeneration Pennsylvania State University–NCAR Mesoscale Model (MM5) run at 18.6and 6.2-kmresolution offline coupled with theWater Flow and Balance SimulationModel
(WaSiM). The MM5 was driven with NCEP reanalysis for 1971–2000 and with Hadley
Centre Coupled Model, version 3 (HadCM3), GCM forcings for 1971–2099. Because
only one regional–global climate model combination was applied, the results may not
give the full range of possible future projections. To describe the Dan spring behavior,
the hydrological model was extended by a bypass approach to allow the fast discharge
components of the Snir to enter the Dan catchment. Simulation results for the period
1976–2000 reveal that the coupled system was able to reproduce the observed discharge
rates in the partially karstic complex terrain to a reasonable extent with the highresolution 6.2-km meteorological input only. The performed future climate simulations
show steadily rising temperatures with 2.2K above the 1976–2000 mean for the period
2031–60 and 3.5K for the period 2070–99. Precipitation trends are insignificant until the
middle of the century, although a decrease of approximately 12% is simulated. For the
end of the century, a reduction in rainfall ranging between 10% and 35%can be expected.
Discharge in the UJR is simulated to decrease by 12%until 2060 and by 26%until 2099,
both related to the 1976–2000mean. The discharge decrease is associated with a lower
number of high river flow years.
Giuseppe Zappa Matthew K. Hawcroft Len Shaffrey Emily Black · David J.
Brayshaw Extratropical cyclones and the projected decline of winter
Mediterranean precipitation in the CMIP5 models, Clim Dyn DOI 10.1007/s00382014-2426-8, 2014
Abstract The Mediterranean region has been identified as a climate change “hot-spot”
due to a projected reduction in precipitation and fresh water availability which has
potentially large socio-economic impacts. To increase confidence in these projections, it
is important to physically understand how this precipitation reduction occurs. This study
quantifies the impact on winter Mediterranean precipitation due to changes in
extratropical cyclones in 17 CMIP5 climate models. In each model, the extratropical
cyclones are objectively tracked and a simple approach is applied to identify the
precipitation associated to each cyclone. This allows us to decompose the Mediterranean
precipitation reduction into a contribution due to changes in the number of cyclones and a
contribution due to changes in the amount of precipitation generated by each cyclone.
The results show that the projected Mediterranean precipitation reduction in winter is
strongly related to a decrease in the number of Mediterranean cyclones. However, the
contribution from changes in the amount of precipitation generated by each cyclone are
also locally important: in the East Mediterranean they amplify the precipitation trend due
to the reduction in the number of cyclones, while in the North Mediterranean they
compensate for it. Some of the processes that determine the opposing cyclone
precipitation intensity responses in the North and East Mediterranean regions are
investigated by exploring the CMIP5 intermodel spread.
Simon O. Krichak & Joseph S. Breitgand & Silvio Gualdi & Steven B. Feldstein
Teleconnection–extreme precipitation relationships over the Mediterranean region
Theor Appl Climatol 117:679–692 DOI 10.1007/s00704-013-1036-4, 2014
Abstract The relationship between five teleconnection patterns (North Atlantic
Oscillation (NAO), Arctic Oscillation (AO), East Atlantic/Western Russian (EAWR)
pattern, Scandinavian (SCAND) pattern, and El Niño Southern Oscillation (ENSO)) and
the frequency of occurrence of days (per month) with extreme precipitation in the EuroMediterranean region is investigated with National Centers for Environmental
Prediction–National Center for Atmospheric Research reanalysis data. To quantify the
teleconnection–precipitation relationships over the Euro-Mediterranean region, linear
correlations are calculated between the monthly teleconnection indices for the five
patterns and time series at each grid point of the monthly frequency of days with extreme
precipitation, focusing on daily precipitation amounts that exceed a particular threshold
value (a 90 % threshold is used). To evaluate dynamical processes, the teleconnection
indices are also correlated with the frequencies of days with extreme values of dynamic
tropopause pressure and precipitable water. The former quantity is used as a proxy for
potential vorticity intrusions and the latter to identify regions of enhanced moisture. The
results of this analysis indicates positive, statistically significant correlations between the
NAO, AO, and SCAND indices and the frequency of extreme precipitation in the western
Mediterranean; positive (negative) correlations between the EAWR index and the
extreme precipitation frequency in the eastern (western) Mediterranean; and a positive
correlation between the Niño3.4 index and the extreme precipitation frequency over the
Iberian Peninsula and the Middle East. For all of the teleconnection patterns other than
ENSO, the dynamic tropopause pressure correlation patterns resemble those for the
precipitation. In contrast, similar precipitation and precipitable water correlation patterns
are observed only for ENSO. These findings suggest that the teleconnections affect the
interannual variation of the frequency of days with extreme precipitation over a large part
of the Euro-Mediterranean region through their impact on the spatial distribution of
regions withenhanced potential vorticity and air moisture.
Simon O. Krichak & Joseph Barkan & Joseph S. Breitgand & Silvio Gualdi &
Steven B. Feldstein The role of the export of tropical moisture into midlatitudes for
extreme precipitation events in the Mediterranean regionTheor Appl Climatol,
121:499–515 DOI 10.1007/s00704-014-1244-6, 2015
Abstract The aims of the study are twofold: firstly, to investigate the role of the export of
humid tropical air in the formation of cool season heavy precipitating events (HPEs) in
the Mediterranean region (MR); and secondly, to examine the possible linkage between
the export of humid tropical air and the multiyear trend in extreme precipitation in the
region. For this purpose, we analyze the spatial distributions of a number of key
atmospheric variables with a reanalysis data for more than 50 intense HPEs for the MR.
The results of this evaluation for both individual and composite events suggest that the
HPEs are associated with atmospheric rivers (ARs). The MR HPEs are being
characterized by the poleward export of humid air of tropical origin into the midlatitude
MR from the Atlantic Ocean and Arabian Sea. These export events appear to be
associated with the effects of hurricanes or intense cyclones in the North Atlantic. It was
also found that the linear trend (for 1979–2013) of the frequency of humid days (days
with precipitable water greater than 20 kg m−2) is consistent with recent changes in the
character of precipitation over the MR and southern Europe.
Annarita Mariotti · Yutong Pan · Ning Zeng Andrea Alessandri Clim Dyn,
44:1437–1456, DOI 10.1007/s00382-015-2487-3, 2015.
Abstract Long-term climate change and decadal variability in the Mediterranean region
during 1860–2100 are investigated based on observational data and the newly available
Coupled Model Intercomparison Project—Phase 5 (CMIP5) experiments. Observational
records show that decadal variability and a general tendency for annual-mean conditions
to be warmer and drier have characterized the Mediterranean during 1860–2005.
Consistency with CMIP5 model simulations including greenhouse gases (GHG), as well
as anthropogenic aerosols and natural forcings, suggest that forced changes have
characterized aspects of Mediterranean climate during this period. Future GHG-forced
change will take place in the midst of decadal variability, both internal and forced, as it
has occurred in the past. However, future rates of forced warming and drying over the
Mediterranean are projected to be higher than in the past century. The degree to which
forced change and internal variability will matter depends on the climatic quantity being
considered. For surface air temperature and Mediterranean Sea annual-mean evaporation
and surface freshwater fluxes, variability and forced change have become comparable
and the forced signal has already emerged from internal variability. For quantities with
large internal variability and relatively small forced signal such as precipitation, forced
change will emerge later on in the twenty-first century over selected regions and seasons.
Regardless, the probability distribution of future precipitation anomalies is progressively
shifting towards drier conditions. Overall, results highlight that both mean projected
forced change and the variability that will accompany forced mean change should be
considered in the development of future climate outlooks.
Shira Raveh-Rubin and Heini Wernli Large-scale wind and precipitation extremes
in the Mediterranean: a climatological analysis for 1979–2012Q. J. R. Meteorol. Soc.
DOI:10.1002/qj.2531, 2015
A new method for identifying high impact large-scale wind and precipitation events in
the extended Mediterranean region is outlined and applied to the European Centre for
Medium-range Weather Forecasts (ECMWF) reanalysis dataset ERA-Interim for the
years 1979–2012. The method highlights large-scale 10m gust and precipitation events
that classify as extreme if integrated over a spatial scale of 1000 km and a temporal scale
of 3 days. The method detects successfully high impact events, and reveals clear seasonal
differences among the subregions of the Mediterranean. Western Mediterranean
precipitation extremes are more intense, and occur mainly in autumn, while eastern
Mediterranean events occur in winter. Composite dynamical analyses of large-scale wind
and precipitation extremes, and a combination of them, highlight coherent dynamical
flow structures associated with the extremes in the different subregions of the
Mediterranean. Precipitation events are preceded by an upper-level trough and strong jet
on its western flank, followed by cyclogenesis (mainly in the western Mediterranean),
and/or amerging of the polar with the subtropical jet over northeastern Africa (in the
eastern Mediterranean). Strong surface wind extremes develop around cyclones that
intensify south of a deep parent cyclone near the exit of a strong anticyclonically curved
jet, propagate eastwards and create a cold and dry northerly wind anomaly at the surface.
Furthermore, combined large-scale wind and precipitation extremes often occur
simultaneously near cyclones, either North Atlantic cyclones, which project the wind and
precipitation into the western Mediterranean, or Mediterranean cyclones. The latter
produce wind extremes over a localized area, which often overlaps entirely with the
region that receives extreme
Michiel Baatsen · Reindert J. Haarsma · Aarnout J. Van Delden · Hylke de Vries
Severe Autumn storms in future Western Europe with a warmer Atlantic Ocean
Clim Dyn 45:949–964DOI 10.1007/s00382-014-2329-8 2015
Abstract Simulations with a very high resolution (~25 km) global climate model indicate
that more severe Autumn storms will impact Europe in a warmer future climate. The
observed increase is mainly attributed to storms with a tropical origin, especially in the
later part of the twenty first century. As their genesis region expands, tropical cyclones
become more intense and their chances of reaching Europe increase. This paper
investigates the properties and evolution of such storms and clarifies the future changes.
The studied tropical cyclones feature a typical evolution of tropical development,
extratropical transition and a re-intensification. A reduction of the transit area between
regions of tropical and extratropical cyclogenesis increases the probability of
reintensification. Many of the modelled storms exhibit hybrid properties in a considerable
part of their life cycle during which they exhibit the hazards of both tropical and
extratropical systems. In addition to tropical cyclones, other systems such as cold core
extratropical storms mainly originating over the Gulf Stream region also increasingly
impact Western Europe. Despite their different history, all of the studied storms have one
striking similarity: they form a warm seclusion. The structure, intensity and frequency of
storms in the present climate are compared to observations using the MERRA and
IBTrACS datasets. Damaging winds associated with the occurrence of a sting jet are
observed in a large fraction of the cyclones during their final stage. Baroclinic instability
is of great importance for the (re-)intensification of the storms. Furthermore, so-called
atmospheric rivers providing tropical air prove to be vital for the intensification through
diabatic heating and will increase considerably in strength in the future, as will the
associated flooding risks