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5.8 Agriculture and forestry
5.8.1 Introduction
The impacts of medium and long-term climate change on agriculture and forestry are
often difficult to analyse separately from non-climate influences related to the
management of the resources (Hafner, 2003). However, there is growing evidence that
processes such as changes in phenology, growing season length and northwards shift of
crops and forest species can be related to climatic change (IPCC-AR4, 2007). There are
also increasing impacts due to an augmented frequency of some extreme events which
can be attributed to climate change.
Potential positive impacts of climate change on agriculture in general are related to,
longer growing seasons and new cropping opportunities in Northern Europe, and
increased photosynthesis and CO2 fertilisation throughout Europe. These possible
benefits are counterbalanced by potentially negative impacts that include increased water
demand and periods of water deficit, loss of soil carbon content, increased pesticide
requirements and crop damages and less cropping opportunities in some regions in
Southern Europe (Olesen and Bindi, 2004; Maracchi et al, 2005, Chmielewski et al.,
2004, Menzel, 2003). In general, changes in atmospheric carbon dioxide levels and
increases in temperature are changing the quality and composition of crops and
grasslands and also the range of native/alien pests and diseases. The latter could affect
not only crops but also livestock and ultimately humans. In addition, the increase in
ozone concentration related to climate change (Meleux et al., 2007) is projected to have
significant negative impact on agriculture mainly in Northern mid-latitudes (Reilly et al.,
2007)
The link of forestry with climate change is twofold. Forests play a fundamental role in
mitigating climate change because they may act as sinks for carbon dioxide. However,
forests are also very vulnerable to changes in temperature, precipitation and extreme
weather events which might have destructive impacts and reduce the carbon sequestration
potential of the forest. Events such as forest fires have an even more negative effect since
destroying the forest increases the amount of carbon dioxide in the atmosphere. The
majority of forests in central Europe are growing faster than in the past, partly because of
regional warming. In contrast, the extended heat-wave of 2003 caused a significant
reduction in biomass production of forests (Gabon, 2005).
Although the economic impacts of climate change on agriculture and forestry in Europe
are very difficult to be determined due to the effects of policies and market influences
and due to the continuous technological development in farming and silviculture
techniques, there is evidence of wider vulnerability for both sectors (see also Chapter 7).
Management actions can counteract but also exacerbate the effects of climatic changes
and will play an important role as measures for adaptation to climate change (AEA,
2007).
The indicators included in this section are related to agricultural production, phenology,
forestry growth and distribution, and to observed and projected impacts of forest fires.
The effect of climate change on soil organic content is also covered in this chapter.
Data availability and quality are essential to monitor trends and threats concerning
European forests, soils and agricultural products. The International Co-operative
Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICPForest), originally set up to monitor the effects of air pollution, now includes surveys that
might also be used to monitor the effects of climate change (e.g. phenology). Another
clear step forward in the collection of relevant information is being achieved by the
establishment of the European Data Centres on Soil and Forestry.
5.8.2 Growing season for agricultural crops
Key Message
•
There is evidence that growing season length has varied in Europe for several
agricultural crops (very high confidence).
•
The longer growing season increases the productivity of crop yields and insect
population and favours the introduction of new species in areas which were not
suitable for these species before. These opportunities are particularly important for
the northern latitudes (high confidence).
•
Locally at southern latitudes, the trend is towards shortening of the growing season
with consequent higher risk of frost damages for the crops due to delayed spring
frost events (high confidence).
Figure 5.8.2.1:
Variation of growing
season length.
Relevance
Increasing air temperatures significantly impact on the duration of the growing season
over large areas in European (Scheifinger et al, 2003). The number of consecutive days
with temperatures above 0°C can be assumed as the period favourable for growth, also
called “frost-free period”. The timing and length of the frost-free period is of interest to
naturalists, farmers and gardeners amongst others. The impact on plants and animals are
largely reported with a clear trend towards earlier appearance dates of spring starting
growth and its prolongation during autumn (Menzel et al, 1999). A longer growing
season permits the proliferation of those species facing optimal conditions for their
development and increase of their productive performances (e.g.: crop yields, insect
population, etc.); the introduction of new species (very sensitive to frost) in areas before
limited by unfavourable thermal conditions. Changes of management practices, e.g.
changes in species grown, different varieties or adaptations of the crop calendar, can
counteract the negative effects of a changing growing season (pests) and capture the
benefits (agricultural crops).
Past trends
Many studies report the lengthening of the period between the dates of occurrence of last
spring frost and first autumn frost. This occurred in the last decades in several areas in
Europe and more generally in the Northern Hemisphere (Keeling et al., 1996; Myneni et
al., 1997; Magnuson et al., 2000; McCarthy et al., 2001; Menzel and Estrella, 2001;
Tucker et al., 2001; Zhou et al., 2001; Walther et al., 2002; Root et al., 2003 Tait et al,
2003, Yan et al., 2002, Robeson 2002, Way et al., 1997). An analysis of the growing
season lengths in Europe between 1975 and 2006 shows a general and clear trend in
lengthening of the growing season. However, in the Mediterranean countries, in the
Black Sea area and in parts of Russia a decline in lengths have been observed.
Frost-free period in
Frost-free period in
The trend is not uniformly spread over
Danmark (DK)
HIGHLANDS AND ISLANDS (UK)
Europe. The highest rates of variation
(about 0.5-0.7 days per year) have been
recorded in central and Southern Spain,
Central Italy, along the Atlantic shores,
on the British Isles, in Denmark and in
the central part of Europe. The
extension of the growing season
Frost-free period in
Frost-free period in
occurred either due to a reduction of
THESSALIA (GR)
EXTREMADURA (ES)
spring frost events or due to a
progressive delay of the occurrence of
fall frost. By contrast, in areas where a
decrease of the length occurred, in
particular in Southern Europe, the
plants are more at risk to frost damages
due to a delay in the last winter-spring Figure 5.8.3.2: Development of frost-free
frost.
periods in selected areas. Source: MARS/STAT
database
300
400
350
250
Nr. of days
Nr. of days
300
200
150
250
200
150
100
100
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2008
2006
2004
2002
2000
1998
1996
1994
1992
1990
1988
1986
50
1984
100
50
1982
150
1980
1976
200
100
1978
1980
250
150
1976
1978
200
1976
300
250
1974
350
300
Nr. of days
400
350
1974
2008
2006
2004
2002
2000
1998
1996
1994
1992
1990
1988
1986
1984
1982
1980
1978
400
1974
Nr. of days
1976
50
1974
50
Projections
Following the observed trends (even more accelerated in the last decade) and according
to the future projections for temperatures increase, a further lengthening of the growing
season (both for earlier onset of spring and delayed of autumn) as well as a northward
shift of species is projected. The latter development is already widely reported (Aerts et
al., 2006). The length of growing season will mainly be influenced by the increase of
temperatures in autumn and spring (Ainsworth and Long, 2005; Norby et al., 2003;
Kimball et al.,28 2002; Jablonski et al., 2002).
According to the IPCC analysis Europe undergoes a warming in all seasons in all
scenarios, but the warming will be greater over Western and Southern Europe in summer
and over Northern and Eastern Europe in winter. Therefore, in these areas a larger
lengthening of growing season is expected, whilst in southern and Western Europe the
limited water availability and the high temperatures stress during summer will affect the
real plant growth negatively.
5.8.3 Timing of the cycle of agricultural crops (agrophenology)
Key Message
•
•
•
There is evidence that flowering and maturity of several species in Europe now
occur two or three weeks earlier than in the past (very high confidence).
The shortening of the phenological phases are expected to continue if the
temperature will keep increasing (high confidence).
Adaptations
in farm in
practices
will be crucial
to beginning
reduce or avoid
negative impacts
Simulated
changes
the occurrence
of the
of flowering
of crops cycle shortening.
of winter wheat between (1975 -2007)
Days/year
<-0.5
-0.5 - -0.3
-0.3 - 0
0 - 0.4
Figure 5.8.3.1: Rate of advance in the yearly date of flowering of winter wheat. The day
of the year of flowering has been simulated by using a crop growth model (CGMS - Crop
Growth Monitoring System) for the period 1975-2007. Source: MARS Database.
* based on observed daily meteo data (AGRI4CAST MARS DB)
Relevance
Changes in crop phenology provide important evidence of responses to recent regional
climate change (IPCC, 2007). Although phenological changes are often influenced by
management practices and new farming technologies, the recent warming in Europe has
clearly advanced a significant part of the agricultural calendar. Specific agrophenological stages are particularly sensitive (e.g.: flowering, grain filling, etc.) to
weather conditions and critical for final yield. The timing of the crop cycle
(agrophenology) determines the productive success of the crop. In general, a longer crop
cycle is strongly correlated to higher yields. In fact, a longer cycle permits to maximize
the thermal energy, the solar radiation and the water resources available. The impact of
unfavourable meteorological conditions and extreme events vary largely according to the
timing of occurrence and the development stage of the crops. However, shortening of
growth period can also help avoiding summer stress conditions in areas prone to drought.
European farmers have already adapted their practices to the changing climate by
selecting suitable varieties or adapting the crop calendar, and can be expected to do so in
the future.
Past trends
Several studies have collected data and observed changes in the phenological phases of
several perennial crops in Europe, such as the advance in the beginning of the growing
season of fruit trees (2.3 days/10 years), cherry tree blossom (2.0 days/10 years), apple
tree blossom (2.2 days/10 years) in agreement with positive anomalies of up to 1.4°C in
mean annual air temperature in Germany (Chmielewski et al., 2004) and the advance of
fruit tree flowering of 1-3 weeks over the last 30 years for apricot and peach trees in
France (Seguin et al., 2004).
An advance of sowing or planting dates has been observed for several agricultural crops,
ranging from 5 days for potatoes in Finland to 10 days for maize and sugar beet in
Germany and 20 days for maize in France (IPCC, 2007).
Grapevine phenology
Wine quality is determined by various parameters: grape variety, rootstock, soil type, cultivation techniques, and
climatic characteristics. The first three are generally constant over time, while cultivation techniques are most often
responsible for long-term variability. Climate influences year-to-year variability and is responsible for variations in the
amount and quality of produced wines.
Wine production areas, and particularly those for premium wines, are limited to regions climatically conducive to
growing grapes with balanced composition and degree to which they reflect their origin (“varietal typicity”). Three
conditions are required: (i) adequate heat accumulation; (ii) low risk of severe frost damage; and (iii) the absence of
extreme heat. Moreover, vines are resistant to limited water availability in summer and it is essential to have no rainfall
during harvest time, in order to increase sugar concentration and reduce disease development.
Observed climate change during recent years determined a general increase of wine quality, mainly due to the increase
of heat and reduction of rainfall,
particularly during the last part of the
ripening period, with a gradual increase
in the potential alcohol levels (Duchen et
al., 2005). Future possible impacts:
• Seasonal shift: moving forward in
time of all the phenological phases
with an increase of frost risk and a
shortening of the ripening period.
As a possible effect, the harvest
time can now fall during periods
with high temperatures, with
negative effect on wine quality.
• Expanding of wine production
areas, to north and more elevated
regions.
• Water stress due to a reduction of
Figure 5.8.3.2 Evolution of potential alcohol levels at harvest for
available water.
• Modification of pest and disease Riesling in Alsace (F). Source: Duchen et al., 2005
development.
• Increase of sugar concentration determining wine with high alcohol and low acidity. The consequence is the
reduced possibility of wine ageing and the poorer phenolic ripening.
• Modification of natural yeast composition.
Projections
Assuming the warming trend will continue, further reductions of the number of days
required for reaching the flower opening (anthesis) and maturity phases may be expected
for areas in Western Europe, where the phenology is currently strongly accelerated
(ECCE, 2005). However, the rate of the reductions can gradually decrease with a further
increase of temperature (+4°C and +6°C hypotheses) due to a reduced efficiency of the
photosynthetic process at high temperatures.
5.8.4 Crop yield variability
Key Message
• Climate and its variability are largely responsible for variations of crop suitability and
productivity in Europe (high confidence).
• Since the beginning of the 21st century, the variability of crop yields increased as a
consequence of the extreme climatic events, e.g. the summer heat of 2003 or the
spring drought of 2007 (very high confidence).
• As a consequence of climatic changes those extreme climatic events are projected to
increase in frequency and magnitude and crop yields are expected to become more
variable. Changes in farming practices and land management can act as riskmitigating measures (high confidence).
Figure 5.8.4.1: A changing climate will affect agro-ecosystems in heterogeneous ways,
with either benefits or negative consequences dominating in different agricultural
regions. Rising atmospheric CO2 concentration, higher temperature, changing patterns of
precipitation, and altered frequencies of extreme events will have significant effects on
crop production, with associated consequences for water resources and pest/disease
distributions. (Rosenzweig at al., 2007)
Relevance
Climate change introduces new uncertainties for the future of the agricultural sector.
Climatic conditions are projected to become more erratic with an increase in the
frequency of extreme events (floods, hurricanes, heat waves, severe droughts) (Parry,
2000). Biomass production of plants, and thus crop yields, are fundamentally determined
by climatic conditions, i.e. the stable availability of energy (radiation, temperature) and
water (rain) to support growth. Other environmental and anthropogenic factors influence
crop yields, such as soil fertility, crop varieties and farming practices. These factors
imply that in principle, many adaptation options are available to adjust agricultural
practices to the changing climate, but that opportunities differ between regions.
Past trends
While the area under arable land decreased for most parts of Western Europe over the last
40 years crop yields have almost continuously increased (source: Eurostat). This trend
persisted into the 21st century, although crop yield variability increased as a consequence
of several extreme meteorological events in short succession: In 2003 a late frost
followed by a severe drought reduced cereal yields over most parts of Europe. In 2005 a
drought severely affected Western Europe (Iberian Peninsula). In 2006 an early drought
was followed by extreme rains during summer, resulting in lower cereal production
especially in Eastern Europe. (EC, Mars Bulletins, 2008) Alexander et al (2006) found a
general increase of the intensity of precipitation events. For the Mediterranean area,
where the climatologic vulnerability is high, several studies found an increasing trend
towards more intense precipitation and a decrease in total precipitation (Alpert et al.,
2002; Maheras et al., 2004, Brunetti et al., 2004). In general, it is difficult to separate the
climate effect from the effect of improved agricultural techniques in the development of
historic crop yield. Also in the future, adaptive management can help reducing the risks
of climate change for agricultural yields, and make better use of opportunities.
Projections
The effect of increasing mean daily temperatures on agricultural yields depends on the
magnitude and geographic extent. The production area of some crops could expand to
northward areas in Europe, e.g for maize. For an increase in mean annual temperature of
2°C, cereal yields are expected to increase not least due to the fertilisation effect of the
increase in CO2 (Parry et al, 2004). However, an increase in mean annual temperature of
4°C or more will shorten the crop cycle and the CO2 effect will not compensate for the
resulting yield loss. Crop yields are also at risk from more intensive precipitation and
prolonged periods of drought in particular in areas bordering the Mediterranean basin.
The figures below show the sensitivity of maize and wheat yields to climate change, as
derived from results of 69 published studies. The studies span a range of precipitation
changes and CO2 concentrations, and vary in how they represent future changes in
climate variability. Responses include cases without adaptation (red dots) and with
adaptation (dark green dots). Adaptation represented in these studies included changes in
planting dates and crop varieties, and shifts from rain-fed to irrigated conditions.
Figure5.8.4.2: Yield variation due to temperature increase. A small increase of
temperature has a positive impact on cereals yield, while a high increase (3-5°C) has a
negative impact. Lines are best-fit polynomials and are used here to summarize results
across studies rather than as a predictive tool. Source: IPCC Report WGII (2007)
5.8.5 Water Requirement
Key Message

Between 1975 and 2006 clear trends, both positive and negative, were evident in
water requirement across Europe, with marked spatial variability. A significant
increase of water demand (50-70%) occurred mainly in Mediterranean areas; large
decreases were recorded mainly in northern and central European regions (very high
confidence).

Current trends and future scenarios depict an increase in the demand for water in
agriculture, potentially rising competition for water between sectors and uses (high
confidence).
Presentation of the main indicator
Figure 5.8.5.1: Variation in the annual meteorological water balance between April and
October (m3/ha/yr) between 1975 and 2007. In areas where the rainfall amount has grown
faster than the increase in temperature (for ex. in NL and DK in the period 1997-99), the
figure shows a reduction of water deficit. The rate of variation of the “meteorological (or
climatic) water balance”, expressed in m3 ha-1 y-1 is calculated as the difference between
the volume of rainfall and the loss by evapotranspiration. A negative “meteorological
water balance” indicates that evapotranspiration exceeds rainfall, and the amount by
which it does so, represents the additional volume of water required from irrigation to
compensate and to maintain the potential crops productivity. In other words, this
indicator provides an estimation of the maximum water volume which is necessary to
ensure that crop growth is not limited by water availability. Source: MARS/Stat database
Relevance
Climate change may affect agriculture primarily through increasing atmospheric CO2,
rising temperatures and changing rainfall. Where rainfall does not limit crop growth,
these conditions allow for earlier sowing dates and enhanced crop growth and yield (see
previous indicators). Where reduced rainfall is predicted, however, the increased
requirement for irrigation water can have an overall negative impact in economic and
environmental terms. In these areas, increased water shortages in the future will enhance
the competition for water between sectors (tourism, agriculture, energy, etc.), particularly
in Southern Europe where the agricultural demand for water is greatest. Several
adaptation options are available to mitigate the risks of water shortage. Increased
irrigation can further burden surface and groundwater resources and increase greenhouse
gas emissions, adding to the mitigation challenge.
Past trends
Systematic observation of water
demand for agriculture do not exist
at European scale, however local
trends cab ne reconstructed by using
meteorological data. On average,
the annual rate of increase of the
water demand is around 50
m3/ha/yr, but in some cases (Italy,
Greece, Maghreb, Central Spain,
Southern France and Germany) it is
above 150-200 m3/ha/yr. Areas with
upward trends in the water balance
(mainly due to an increase in
rainfall), have been observed in the
Balkan Peninsula, the Alpine
region, Scandinavia, Scotland, Figure 5.8.5.2: In the Mediterranean area, a
Benelux, the Czech Republic, worsening climatic water deficit has been
Slovakia, Poland and Hungary, as observed over the past 32 years (1975-2006)
well as in many Turkish areas.
Projections
No quantitative projections of future irrigation demand are available. Many climatic
projections for Europe (IPCC, 2007) foresee a very likely precipitation increase in the
North and a decrease in the South, especially during the summer. Also the extremes of
daily precipitation will increase in the north and the annual number of rainy days will
decrease in the Mediterranean (ref. Ch. 5.7.5 River flow drought). Therefore, the risk of
summer drought is likely to increase in central Europe and in the Mediterranean area.
Agricultural crops will be affected, among other factors, in positive and negative ways by
changes in the length and timing of the vegetative cycle. Adaptation in crop management
will be necessary in order to try to avoid that crucial development stages sensitive to
water-stress (flowering, grain filling, etc.) will occur during generally dry periods.
5.8.6 Forest Growth
•
In much of continental Europe, the majority of forests are growing faster now than in the
early 20th century (High confidence).
•
A changing climate will favour certain species in some forest locations, while making
conditions worse for others, leading to substantial shifts in vegetation distribution (Very high
confidence).
•
The distribution and phenology of other plant and animal species (both pests and
pollinators) is likely to change, leading to further alterations in competition dynamics in forests
that will be difficult to predict (High confidence).
• Drought periods and warm winters are increasing pests populations and further weakening
forests (High confidence).
Presentation of the main indicator
Figure 5.8.6.1: Modelled current (left hand side: year 2000) and future (right hand side: year
2100, scenario A1B, NCAR CCM3 model ) of the 10 most dominant European Forest Categories
(EEA, 2006), modelled to evaluate the change of habitat suitability. Source: Casalegno et al.
2007.
Relevance
Forests accumulate 77% of the global carbon pool in the vegetation biomass and hence play an
important role in the global carbon cycle (Dixon et al., 1994; IPCC, 2007). The carbon sink of
European forests is currently estimated to offset about 10% of European fossil fuel emissions
(Janssens et al. 2005, EEA, 2007). Forests and woodlands provide many things that society
values, including food, marketable products, medicines, biodiversity, carbon reservoirs and
opportunities for recreation. In addition, they regulate biogeochemical cycles and contribute to
soil and water conservation. Changes in global climate and atmospheric composition are likely to
have an impact on most of these goods and services, with significant impacts on socioeconomic
systems (Winnett, 1998).
Management has a significant influence on the development of the growing stock and forest
productivity. Adaptation measures include changes to plantation practices and forest
management, the planting of different species mixtures, better matching of the species to the
specific site, and the planting of similar species from their places of origin and non-native species
in anticipation of climate change (Broadmeadow et al., 2003) and the restoration of forest
typologies that could offer greater flexibility to climate changed (Kolling, 2008).
Past trends
For many centuries, most European forests were overexploited. Growth rates were reduced and
biomass stocks were depleted until the middle of the twentieth century, when growth rates started
to recover (Spieker et al. 1996; ICP Forests, 2005). Much of this increase can be attributed to
advances in forest management practices, genetic improvement and, in central Europe, the
cessation of site-degrading practices such as litter collection for fuel. It is also very likely that
increasing temperatures and CO2 concentrations, nitrogen deposition, and reduction of air
pollution (SO2) have had a positive effect on forest growth. Trees have long been known to
respond to changes in climate: variations in tree-ring widths from one year to the next are
recognized as an important source of climatic information over time (see Chapter 2).
Several studies have already noted changes in dates of budburst and therefore longer growing
season in several species (see Section 5.5.3), shifts in tree-line and changes in species distribution
(see Section 5.5.2). A north-east shift of forest categories has already been observed for European
forest species (Bakkens 2002, Harrison et al. 2006).
Projections
Tree growth is controlled by complex interactions between climate and non-climate related
factors, with forest management also having a significant effect. Possible future responses of
forests to climate change include increased growth rates, tree-line movements, changes to forest
growth, phenology, species composition, increased fire incidence (see Chapter 5.5.8), more
severe droughts in some areas, increased storm damage, and increased insect and pathogen
damage (Eastaugh/IUFRO 2008). Taken together this is likely to lead to a changed pattern of
forest cover in the future. Simulation of the IPCC SRES A1B scenario for the period 2070-2100
shows a general trend of a south-west to north-east shift in suitable forest categories habitat
(Casalegno et al. 2007).
Although climate change is anticipated to have an overall positive effect on growing stocks in
Northern Europe, negative effects are also projected in some regions (e.g. drought and fire pose
an increasing risk to Mediterranean forests), making overall projections difficult.
Warmer winter weather is likely to increase
productivity by extending the length of the
growing season (Cannell et al., 1998).
Reduced summer rainfall may reduce tree growth and
severe droughts may kill increasing numbers of trees.
Elevated atmospheric CO2 concentrations can
have a fertilising effect.
Elevated atmospheric ozone concentrations may have a
negative impact on growth (Sitch et al., 2007; Karnosky
et al., 2005).
Cold and snow-related damage are likely to
become less common.
Violent storms may occur more often, and more trees
are likely to be damaged or blown down.
Possible increase in spring frost damage as trees
become more susceptible through earlier leafing.
Damage by forest fires and insect pests is projected to
increase.
5.8.7 Forest fire danger
Key Message
• Under a warmer climate more severe fire weather is expected and, as a consequence,
more area burned, more ignitions and longer fire seasons (high confidence).
• Climate change will increase the fire potential during summer months, especially in
southern and central Europe (high confidence).
• The period in which fire danger exists will be longer in the future due to climate
change, with a likely increase of the frequency of extreme fire danger days in spring
and autumn (high confidence).
Figure 5.8.6.1: Past trends of fire danger level from 1958-2006 using the Seasonal Severity
Rating (SSR). The map indicates the increase of fire danger in relative terms, i.e. as a % of a
given absolute value which is not shown in the figure. EUR Technical Report n. XXX
Relevance
Wildfires are a serious threat to forests and ecosystems in Europe and climate is the most
important driving force affecting fire potential changes over time (Flannigan et al. 2000).
Although it is generally recognized that forest fire occurrence in Europe is mostly due to
causes of an anthropogenic nature, the total burned area changes significantly from year
to year largely because of weather conditions. Changes in fire regimes may have strong
impacts on natural resources and ecosystems stability, with consequent direct and indirect
economic losses. On other hand active forest management and fire management practices
can counteract the impacts of a changing climate to some extent.
Past trends
Fire risk depends on many factors of a different nature that change over time (such as
e.g., weather, fuel load, fuel type and condition, forest management practices, socioeconomic context…). Historical fire series can be used to support statements on trend but
unfortunately long and consistent time series of fire events are rarely available in Europe.
In addition, by looking at the historical fire series alone, it is difficult to get a clear
picture and recognize the effect of climate on fire potential. In contrast meteorological fire
danger indices, which are designed to rate the component of fire risk dependent on weather
conditions, can be usefully employed to analyze fire trend in a consistent way throughout longer
time series. These indices, normally applied on a daily bases, can be summarized on a seasonal
basis to rate the overall fire potential of a given year (seasonal fire severity) due to meteorological
conditions. The index of Seasonal Severity Rating (SSR) has been derived from daily values of
Van Wagner’s Fire Weather Index (FWI, Van Wagner 1987) the fire danger assessment method
most widely applied all over the world (San Miguel-Ayanz et al. 2003). Results of a recent
study on SSR development are shown in Figure 5.8.6.1. The average trend 1958-2006
was computed for all the grid cells, but it resulted to be statistically significant only for
21% of the cases (15% positive and 6% negative), which appear to be concentrated in
specific geographical areas (see Figure 5.8.6.1.).
Projections
Future projections were derived for the IPCC SRES scenario A2, processing data from
the PRUDENCE data archive, namely the daily high resolution data (12 km) from
HIRHAM model run by DMI, for the time periods 1960-90 (control) and 2070-2100
(projections) (see Figure 5.8.6.2). Results confirm in Europe, projections assessed for
North America (Flannigan et al. 2005) with a significant increase of fire potential, an
enlargement of the fire prone area and a lengthening of the fire season.
Figure 5.8.6.2. Projected (2071-2100) and control (1961-1990) three-monthly fire danger levels in Europe
for the IPCC SRES high emissions A2 climate change scenario, HIRAM. Fire danger in winter months
(DJF) is not shown because negligible. Source: EUR Technical Report n. XXX
5.8.8 Soil Organic Carbon
Key Messages
o Soil in the EU contains around 71*109 tons (or 71 gigatons, Gt) of organic carbon,
nearly 10% of the carbon accumulated in the atmosphere) An increase in temperature
and a reduction in moisture tend to accelerate decomposition of organic material and
subsequently lead to a decline in soil organic carbon (SOC) stocks in Europe (high
confidence).
o
Changes in SOC have already been observed in measurements in various European regions
over the last 25 years (very high confidence)
o
The projected changes in the climate during the 21st century will make soils a source
of CO2 in most areas of the EU. To counterbalance the climate-induced decline of
carbon levels in soil adapted land use and management practices can be implemented
(high confidence).
Figure 5.8.8.1 Changes in soil
organic carbon contents across
England and Wales between 1978
and 2003. a) Carbon contents in
the original samplings (1978-83),
and b) rates of change calculated
from the changes over the
different sampling intervals (19942003).
Source: Bellamy et al., 2005
Relevance
Organic carbon in the soil is not a static component, but part of the carbon cycle, which
includes the atmosphere, water and constituents of the above and below-ground
biosphere. The main source of organic carbon is provided by organisms that synthesize
their food from inorganic substances (autotrophic), such as photosynthesising plants. In
this process atmospheric carbon is used to build organic materials and enters the soil
layers through decomposition and the formation of humus.
Climatic conditions strongly influence both the trends and rates of the accumulation and
transformation of organic substances in the soil. Increases in temperature and aridity lead
to a decrease of the amount of organic carbon in soil in areas thus affected. Lower levels
of organic carbon in the soil are generally detrimental to soil fertility and tend to increase
soil compaction, which subsequently leads to increases in surface water runoff and
erosion. Other effects of lower organic carbon levels are a depletion of biodiversity and
an increased susceptibility to acid or alkaline conditions. The projected changes to the
climate cause accelerated rates in the release of CO2 from the soil, which contributes to
higher GHG concentrations in the atmosphere (Janssens, 2004, Bellamy, 2005) .
The main measures to reduce the detrimental effect of higher temperatures combined
with lower soil moisture on the amount of soil organic carbon concern changes in land
cover and adapted practices of land management (Liski et al., 2002; Janssens et al., 2004;
Smith et el., 2005, 2006). Under the same climatic conditions grassland and forests tend
to have higher stocks of organic carbon than arable land and are seen as net sinks for
carbon (Vleeshouwers and Verhagen, 2002). Land management practices aim at
increasing the net primary production and reducing losses of above-ground biomass from
decomposition. Adaptive measures on agricultural land are changes in farming practices,
such as a reduction in tilling or retaining crop residues after harvesting.
Past trends
In the past changes in organic carbon in the soil were largely driven by conversion of
land for the production of agricultural crops and long-term monitoring activities
concentrate on agricultural land, such as the Rothamstead long-term experiments
(Rothamstead Research, 2006). Peat lands in Europe have formed a significant sink for
atmospheric CO2 since the last glacial maximum. Currently they are estimated to hold ca.
42 Gt carbon in the form of peat and are therefore a considerable component in the
European carbon budget.” (Byrne et al., 2004). The annual loss in carbon due to drainage
is in the range of 0 to 47 gCm−2 (Lappalainen, 1996). A survey of Belgian croplands
(210,000 soil samples taken between 1989 and 1999) indicates a mean annual loss in
organic carbon of 76 gCm−2 (Sleutel et al., 2003). A large-scale inventory in Austria
estimated that croplands were losing 24 gCm−2 annually (Dersch and Boehm, 1997). A
general intensification of farming in the past is likely to exceed the effect of changes in
the climate on soil organic carbon on agricultural land.
Projections
The amount of organic carbon in the soil is largely determined by balancing the net
primary production (NPP) from vegetation with the rate of decomposition of the organic
material. Without an increase in NPP soil carbon for cropland may decrease by 8.8 to
12.3 t C ha-1. When including changes in NPP and technological advances the amount of
organic carbon on cropland could increased by 1-7 t C ha-1 (Smith, et al., 2005).
Figure 5.8.8.2: Projected changes of soil organic carbon in the EU for cropland for the
IPCC SRES A2 scenario up to 2080. The map (left) shows that climate change can cause
loss (red-colour) of SOC for most areas in Europe. This decline can be reversed (bluecolour) if measures enhancing soil carbon (adaptation) are implemented. As these are
modelled data, the projected developments should be regarded with caution. Source:
Smith et al., 2005.
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