Download MODIFICATION on CROP WATER DEMANDS under ADAPTATION

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2nd World Irrigation Forum (WIF2)
6-8 November 2016, Chiang Mai, Thailand
MODIFICATION ON CROP WATER DEMANDS UNDER
ADAPTATION ACTIONS TO CLIMATE CHANGE (Submission
Number)
Waldo Ojeda-Bustamante1, Nahun H. García-Villanueva2 and
Mauro Iñiguez-Covarrubias3
ABSTRACT
It is well documented that climate change is inevitable and that farmers need to adapt
to changes in the projected climate. Changes in water demands for a Mexican
irrigation district were assessed using an irrigation scheduling model. The impact of
two potential adaptations actions -changing planting date and using longer season
varieties- on water demands were estimated and compared with a baseline scenario.
Two cropping plans, wet and dry, were selected from the last 15 water years with
actual climatology (1961–1990) taken as reference and three A1B climate change
projections (2011-2040, 2041-2070, and 2071-2098). Cumulative and Daily irrigations
demands were generated for each agricultural season considering potential
adaptations actions. Results show that there are clear trends that without adaptations,
water demands will decrease as increasing temperature will reduce season length in
annual crops. However, as farmers respond to climate change with adaptation actions
to maintain actual yields, water demand can be higher than non-adaptation/baseline
values. Results indicate that the potential impacts of climate change depends not only
on climate changes per se, but also on agricultural management changes with
repercussions on peak and cumulative demands on crop water. Therefore, adaptation
actions must be analyzed with care for minimizing agricultural risk.
Keywords: Adaptation strategies, Irrigation schemes, Climate change, Regional
Climate Models, Crop water requirement, Mexico.
1.
INTRODUCTION
Irrigation is a major adaptation action of agriculture to climate variability; because it
increases crop yields and reduces the risk of crop failure (Hoff et al. 2009). Several
irrigated regions in Mexico have high water demand due to climate variability, water
scarcity and rapid population growth. Reducing water demand requires a more
efficient and sustainable use of water resources (Schütze & Schmitz 2010). Climate
change is expected to have serious impacts on water resources and in consequence
on irrigated agriculture, in both water demand and supply (Yano et al. 2007).
Changes in temperature and precipitation will affect irrigation demands (Allen et al.
1991; Moratiel et al. 2010). These demands depend not only on changes in
evapotranspiration and precipitation but also on crop management. However, their
estimation is complicated due not only to an increase in temperature and carbon
dioxide but also due to changes in plant phenology and adaptation responses from
farmers.
1
Irrigation Engineering Department Head, Instituto Mexicano de Tecnología del Agua (IMTA). Paseo
Cuauhnáhuac 8532, Jiutepec, Mor. México. CP. 62550.); E-mail: [email protected]
2
Irrigation & Drainage Coordinator, Instituto Mexicano de Tecnología del Agua (IMTA). Paseo
Cuauhnáhuac 8532, Jiutepec, Mor. México. CP. 62550.); E-mail: [email protected]
3
Researcher, Instituto Mexicano de Tecnología del Agua (IMTA). Paseo Cuauhnáhuac 8532, Jiutepec,
Mor. México. CP. 62550.); E-mail: [email protected]
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Studies about climate change impacts on agriculture are crucial for short or long-term
irrigation management adjustment to changing weather conditions. Although the
impact of climate change of irrigated land has been a recurrent study subject (Allen et
al. 1991; Zhang et al. 2008), there is a need to analyze these impacts locally with
information validated on the field, given the spatial and temporal variability related to
climate change projections (Goyal 2004). Moreover, the effect of potential adaptation
practices on crop water requirements has not been analyzed at a large scale
considering changes in crops season length due to warming, most climate change
research has been focused on crop productivity impacts (Rosenzweig & Parry 1994;
Ludwig & Asseng 2010). In consequence, the purpose of this paper is to study the
effect of adaptation actions on crop water requirements considering the “Rio Fuerte”
irrigation district (Sinaloa, Mexico) as a case study. The approach taken is to estimate
crop water requirement using a water-balance based system for baseline (1961–
1990) and 2055 (2041–2070) climate scenarios, simulating changes in crop length
using the growing degree-day concept. The assessment of impact and adaptation
strategies because of climate change intensification is very important for Mexico´s
food security and economy, since the studied region is one of the larger grain
suppliers from irrigated agriculture.
2.
METHODS
2.1
Case study: irrigation district 075
Irrigation District (ID) 075 is organized in 13 Water User Associations (WUAs). ID-075
is supplied by two reservoirs using two major open channels. The global district
efficiency was estimated about 40% from reservoir to farm due to unlined open-canal
networks and surface-based irrigation. The methodology was applied to the “Santa
Rosa” Water User Association (SR-WUA), which is the larger WUA at Irrigation
District 075 (ID-075) “Río Fuerte”, located in the northern part of the state of Sinaloa,
México; 25.4-26.1° N, and 108.4-109.4° W, and an average altitude of 20 m. The ID075 has a farm database with detailed irrigation service information for the last 15
agricultural years, which has been generated with the continuous use of the real-time
irrigation forecast system (Spriter) (Ojeda-Bustamante et al., 2007). This database
was used to obtain the crop plan for a typical water year, which in Mexico starts on
October 1 (Julian day 274) and goes through September 31 of the following calendar
year.
Changes in volume availability in ID-075 reservoirs induce drastic changes in
cropping. In consequence, irrigation managers restrict double crops and high water
demand crops in dry years, concentrating crops in Fall-Winter season and reducing or
cancelling Summer-Spring season. Therefore, two cropping plans were used to
analyze two contrasting water years, one for a wet year and other for a dry year. The
wet and dry years were the water years with the highest (42,023 ha) and lowest
(31,121 ha) cropped area for the last 15 water years. Actual SR-WUA command area
is 31,121 ha. Since Spring-Summer (SS) crops are mainly double crops, command
area is cropped once in dry year having only Fall-Winter (FW) and Perennial seasons
(PER). Cropping plans indicates that perennial crops’ area has been halved from 30%
two decades ago to 15% of the command area. Annual crops cover 88.9 and 85.0%,
for the wet and dry year, respectively, out of which 70.8 and 100% belong to the FW
season and 29.2 and 0% are SS season crops, for the wet and dry year, respectively.
The main crops (Table 1) for FW season are Zea mays (corn), Phaseolus vulgaris
(common beans), Solanumtuberosum (potato), Solanum lycopersicum (tomato) and
other horticultural crops. During the SS season the main crops are: Sorghumbicolor
(sorghum), corn and other horticultural crops. Saccharum oficinarum L. (sugarcane) is
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the main perennial crop, other perennial crops are forages (mainly Medicago sativa,
alfalfa), and some orchard crops (mainly Mangifera indica, mango). In dry years, the
SS area is reduced and SS corn is replaced by SS sorghum as table 1 shows.
Sugarcane area is also reduced in dry years. With 62% of the area, the FW season
has become corn monocrop in the last two decades.
In the SR-WUA there is a broad planting period for crops during a typical water year.
The greatest surface established with the four main crops in the Fall-Winter (FW)
season takes place during the winter period from Julian day 280 to the 15 th the
following year (beginning of October to mid-January). With the exception of tomato,
which has a broad sowing period, the harvesting period for FW crops is concentrated
in the period from Julian day 1 to day 140 (from the beginning of January to midMay).Water availability induces drastic changes in cropping for dry years. The FW
season is the main season in terms of cropped area, with secondary area from
perennial crops and SS season highly depending on water availability. In very dry
years, SS season cropping is reduced or cancelled.
2.2
Climate change projections and datasets
The IPCC in its Fourth Assessment Report considers 23 CGCMs, which include six
different scenarios for Greenhouse Gases (GHG) emissions known as SRES
scenarios: B1, B2, A1T, A1B, A1F1, and A2 (IPCC 2000). In this study, the medium
moderate (A1B) emission scenario was used; it is the most frequently used scenario
in climate change studies. A1B considers that society will use all renewable and
limited energy sources, including fossil fuels, in a balanced manner, (IPCC 2007).
Adequate downscaling of CGCM climatic projections is necessary to study impacts of
climate change at local to regional scales (Yano et al. 2007). Therefore, monthly
regional climate projections for the 2011-2098 period were used, with a regular grid of
0.5°x0.5°(~50x50 km) derived by statistical downscaling from CGCM model data as
reported by Montero et al. (2013). Since there are considerable variations among
climate models and there is no unique CGCM that replicates past Mexican
climatology, a probability distribution of future climate change was used to combine
different CGCMs in a single climate ensemble of CGCMs that has been recognized
as preferred instead of using an individual CGCM (Winkler et al. 2011). The projected
precipitation and air temperature (maximum and minimum) data were obtained
through weighted averages of the best CGCM projections for Mexico, available at the
IPCC data distribution center (www.ipcc.data.org), using the Reliability Ensemble
Averaging method (REA) proposed by Giorgi & Mearns (2002; 2003). This method
allowed generating a “mean” climate change projection based on probabilistic
ensemble projections weighted of 23 CGCM considering combined individual model
bias and model convergence to ensemble mean.
Climatic data series were divided in four time periods: P0, P1, P2, and P3. The first, P0,
is related to the recent past and corresponds to the average of climate variables for
the 1961 to 1990 base period. The P1, P2, and P3 scenarios define the average of
monthly values for periods between 2014 and 2040, 2041 and 2070, and 2071 and
2098, respectively. Average monthly values were generated for the climate variables
of temperature and precipitation for each time period for A1B scenario. The climate
data for the 1961 to 1990 period were obtained from “Los Mochis” meteorological
station (25.82° N, 109.0° W, and 14 m altitude), which is considered representative of
the study area as reported by Ojeda-Bustamante et al. (2011).
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2.3
Water demand estimation
The estimation of crop water requirements during a water year for large irrigation
zones was estimated with a developed computer program, Reqgo-ZR, equivalent to
CropWat (Clarke et al. 1998) which consider growth duration as a function of
cumulative growing degree days. The daily evapotranspiration calculation process
used weighted averaged as a function of cropped area for each crop in day
considered.
2.4
Cropping Adaptations
Climate change will impose new challenges to irrigation managers as water demand
will change spatially and temporary, and may increase, as climate change intensifies
and farmers adopt several actions to reduce its impact on crops. Since there are
various driving factors, it is difficult to make predictions on cropping patterns changes
by impact of climate (Perez Urrestarazu et al. 2010). However, it is possible to
establish locally the most likely adaptation actions. Ojeda-Bustamante et al. (2011)
reported two adaptation farmers’ responses to maintain actual crop productivity in a
Mexican Irrigation district: use of longer duration varieties/hybrids and reduction of
planting dates toward colder season as warming intensifies in the future. In this way,
four adaptation actions are analyzed in terms of expected cropping management
changes:
(i)
Without Adaptation (WA). This reference case, called “Dumb farmer” scenario
(Rosenberg 1992), assumes that no attempts to adjust or adapt the farms to
the climate change will be made. Farmers will act as if nothing has changed
same planting date and varieties as used today.
(ii)
Adjusting Planting Season (APS). As warming intensifies, it is assumed that
farmers will move the planting period to cold periods to create a longer
growing season. It was assumed no change in crop pattern.
(iii) Using Longer season Varieties (LV). As warming intensifies, it is assumed
that farmers will use longer-season varieties that will be tolerant to thermal
and drought stress, and which can endure higher temperatures than those
present today.
(iv) A mixed approach (AP+V). Both adaptations alternatives are implanted:
adjusting planting season and new longer-season varieties.
The four adaptation cases were simulated and crop water requirements were
estimated for the wet year, peak year, considering three time periods P1, P2, and P3.
This analysis is very useful to estimate effect of adaptation actions on crop water
requirements that can also provide information about changes in canal capacity and
in the irrigation service.
3.
RESULTS AND DISCUSSION
3.1
Climate change projections
The average trendline projected by CGCM models indicates an annual increase in
average temperature of 0.03 °C per year in the 2010-2098 period for ID-075,
considering the A1B emissions scenario. The average monthly daily temperature,
compared to P0, will increase in average 1.0, 2.2 and 3.0 °C during periods P 1, P2 and
P3, respectively. The annual variation of precipitation will decrease less than 30% by
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the end of the century, as compared to the average P 0 value. Annual rain will
decrease in average 62, 70 and 110 mm during the P1, P2 and P3 periods.
An annual accumulated ETO value of 1554 mm was estimated for the base period P 0.
When introducing projections into the meteorological variables for the A1B emissions
scenario, an increase in annual ETO was estimated, as compared to P0, of 3, 6 and
10% in the P1, P2 and P3 periods.
3.2
CC Impact on corn water requirements
The effect of A1B warming scenario was simulated on FW corn water requirements
for the same planting day (November 15) considering period P2. Without adaptation,
crop water requirement (peak and cumulative) will be lower in the future (WA-P2
curve), with a shifting of peak demand, with respect to actual (WA-P0) as Figure 1
indicates, due to a shortened growing season. This ET decrease, as reported by Yano
et al. (2007), can be attributed to decreases in growing days and leaf area due to
temperature rise and in transpiration due to stomatal closure regardless of increased
evaporative demand. To counteract this effect, it will be necessary in the future to use
cultivars with greater heat requirements (longer season) to maintain yield and
equivalent length season.However, maintaining similar length of growing season in
the future as actual will generate a higher peak and cumulative crop water
requirement (Curve AV-P2) as Figure 1 shows for the middle of this century. As
reference, it is also shown on Figure 1 the actual curve for baseline period (WA-P0).
Peak ETp values were 5.5, 5.0 and 5.7 mm/d; and cumulative ET p were 512, 442, and
546 mm for WA-P0, WA-P2, and LV-P2 curves, respectively.
Figure 1. FWCorn water requirement (ET p) with (AV) and without (WA) adaptation
for mid of century (P2) for a planting date November 15. As a reference the
actual curve is shown (Po).
3.3
Impact of climate change on daily water demands
Irrigation system must be designed based on estimates of what flows will be
demanded along the water year. Figure 2 integrates daily demand flow curves
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considering several adaptations actions for the wet water year. Simulation results
indicated that for mid-century (Period P2) the use of longer-season cultivars (LV) will
have more pronounced effect in daily flow base than the reduction of planting season
(APS) as climate change intensifies during present century. Without adaptation, the
increase in temperature will shorten the growing season of all annual crops,
generating a peak shift; these trends are similar to those reported by OjedaBustamante et al. (2011). Combined adoptions of adaptation actions (AP+V) can
generate higher, peak and cumulative, crop water requirements than actual values as
Figure 2 shows.
3.4
Impact of climate change on cumulative crop water requirements
Assuming than future crop patterns remain similar to the baseline period, crop water
demand will decrease about 11.7% at the end of century. Higher values can be
obtained if PER and SS crops cover more area than actual values. Future climate
change projections indicate warmer and drier environments with respect to the
baseline period (P0). An increase in air temperature will cause a reduction of growing
season duration for annual crops. Under these conditions and for adaptation cases
WA and APS, the cumulative crop water demands are likely to decrease due to the
fact that reduction of crop season has a major impact on the increase of reference
evapotranspiration. The decrease in cumulative crop water demand was more
pronounced for WA case than for APS, as warming intensifies from the current period
to the end of the century. The reduced crop water use will also implicate reduced
yields. Using longer season crop varieties (LV) to recover actual duration of crops’
season can be a viable adaptation, however it will have a major change in crop water
demands, as Table 1 indicates. It can be concluded that cumulative crop water
requirements at irrigation scheme level are expected to decrease in the future climate
when no adaptations are considered as found by Moratiel et al. (2010) and OjedaBustamante et al. (2011). The use of longer season varieties as adaptation strategy
will recover actual crop duration but will increase crop water demands, to higher
values than actual as Table 1 indicates. However, climate change might not generate
high changes in crop water demands as also reported by Islam et al. (2012).
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Figure 2. Water flow demanded under several adaptation actions for mid of century
(P2) for the wet water year. As a reference the actual curve is shown (WAP0).
Table 1. Cumulative crop water requirements (in mm) for the wet year considering
four adaptation actions during for four time periods according A1B emission
scenario. In parenthesis is shown the corresponding change in percentage
with respect reference period P0
Adaptation action
P0
P1
P2
P3
671.3
641.0 (-3.4%)
628.5 (-5.3%)
598.4 (-9.8)
Adjusting planting dates (APS)
649.9 (-2.0%)
642.6 (-3.1%)
629.9 (-5.1)
Longer season varieties (LV)
664.2 (+0.1%)
707.6 (+6.7%)
754.5 (+13.7)
Adjusting planting and varieties
(AP+V)
671.9 (+1.3%)
717.0 (+8.1%)
780.4 (+17.6)
Without adaptation (WA)
Results also indicate that without adaptation actions peak crop water requirement can
be reduced in 27% at the end of the century. However, when adjusting planting dates
is considered this reduction is lesser (19%)? It can increase 1.1% when using longer
season varieties or about 8.3% when using both adaptations actions. However, it
must be also considered inter-annual variation of volumes available for irrigation due
to climate variability. For the study zone, this variation is about 26% between dry and
wet years.
Above results are valid for the study case, where Fall-Winter season concentrate
most crops. Important differences can be found in other cases where the SpringSummer and Perennial seasons have similar o higher cropped areas than Fall-Winter
season.
It should be mentioned that this analysis assumed the A1B emission scenario and did
not consider the combinations of rising temperature and CO 2 that may result in
positive or negative effects on water demands and crop yields, depending on other
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factors. In the present study, we did not considered factors rather than temperature,
and the associated water demands changes as a result of several adaptations
actions. It was assumed no phytosanitary and weeds limitation on crop growth and
yield under both current and future climate scenarios. Agronomic practices,
technological development and land use were also assumed similar in the future.
Therefore, further research is required to clarify the effect of other response variables
and potential adaptations and their possible interactions in several irrigation districts
under contrasting climatic and management conditions.
4.
CONCLUSIONS
Using an ensemble of 23 Global Climate Models projections, it was simulated the
changes in water demand at irrigation scheme scale during this century. This paper
has analyzed changes in crop water requirements due to expected adaptations to
climate change for a typical Mexican irrigation district. The result shows that without
adaptation, a decrease is expected in cumulative and peak crop water demand as
warming intensifies is response to season length shortening in annual crops. As
farmers respond with adaptation actions such as the use of longer duration cultivars
and compacting plating dates, water demands can be higher as shown for the study
case. Therefore, to maintain actual performance, the irrigation network and service
will need adjustment to fit future water demand when adaptations actions are
simultaneously implemented by irrigation managers and farmers.
Results indicate that without adaptation actions peak crop water requirement can be
reduced in 27% at the end of the century. However, it must be also considered interannual variation of volumes available for irrigation due to climate variability. For the
study zone, this variation is about 26% between dry and wet years.
Assessment of potential impacts of climate change on irrigated agriculture must not
only analyze changes on meteorological variables but also repercussion on
responses variables on crop water demands, peak and cumulative, considering
potential famers actions, such changes in agricultural management, and uncertainty
in results from Coupled General Circulation Models. Therefore adaptation actions
must be analyzed with care for minimizing problems on canal capacity and irrigation
service at peak water demand period.
It is also necessary to analyze in detail other viable adaptation actions no studied in
this paper such as crop reconversion and the use of deficit irrigation, water
conservation and harvesting techniques in irrigated agriculture. As shown in the
paper, changes in water availability due to climate variability have more profound
changes in crop water demands that those attributed to climate change impacts.
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