Climate-Determined Suitability of the Water Saving Technology "Alternate Wetting and Drying" in Rice Systems: A Scalable Methodology demonstrated for a Province in the Philippines
December
Climate-Determined Suitability of the Water Saving Technology "Alternate Wetting and Drying" in Rice Systems: A Scalable Methodology demonstrated for a Province in the Philippines
Andrew Nelson 0 1
Reiner Wassmann 0 1
Bjoern Ole Sander 0 1
Leo Kris Palao 0 1
0 1 Faculty of Geo-Information and Earth Observation (ITC), University of Twente , Enschede 7500 AE , The Netherlands , 2 International Rice Research Institute (IRRI) , Los Baños 4031 , Philippines
1 Editor: Paul C. Struik, Wageningen University , NETHERLANDS
-
OPEN ACCESS
70% of the world’s freshwater is used for irrigated agriculture and demand is expected to
increase to meet future food security requirements. In Asia, rice accounts for the largest
proportion of irrigated water use and reducing or conserving water in rice systems has been a
long standing goal in agricultural research. The Alternate Wetting and Drying (AWD)
technique has been developed to reduce water use by up to 30% compared to the continuously
flooded conditions typically found in rice systems, while not impacting yield. AWD also
reduces methane emissions produced by anaerobic archae and hence has applications for
reducing water use and greenhouse gas emissions. Although AWD is being promoted
across Asia, there have been no attempts to estimate the suitable area for this promising
technology on a large scale. We present and demonstrate a spatial and temporal climate
suitability assessment method for AWD that can be widely applied across rice systems in
Asia. We use a simple water balance model and easily available spatial and temporal
information on rice area, rice seasonality, rainfall, potential evapotranspiration and soil
percolation rates to assess the suitable area per season. We apply the model to Cagayan province
in the Philippines and conduct a sensitivity analysis to account for uncertainties in soil
percolation and suitability classification. As expected, the entire dry season is climatically
suitable for AWD for all scenarios. A further 60% of the wet season area is found suitable
contradicting general perceptions that AWD would not be feasible in the wet season and
showing that spatial and temporal assessments are necessary to explore the full potential
of AWD.
Funding: AN, RW, and LKP received support from
The CGIAR Research Program on Rice: Global Rice
Science Partnership (GRISP), http://www.grisp.net/
main/summary. BOS received support from The
CGIAR Research Program on Climate Change,
Agriculture and Food Security (CCAFS), https://ccafs.
cgiar.org/. BOS received support from Climate and
Clean Air Coalition (CCAC), http://www.ccacoalition.
org/. The funders had no role in study design, data
collection and analysis, decision to publish, or
preparation of the manuscript.
Introduction: Irrigation for field crops
Quantity and inefficiency
Irrigated agriculture is one of the major consumers of freshwater accounting for 70% of water
withdrawal globally [
1,2
]. At sub-continental scale, these percentages can be even higher, e.g.
92% in mainland Southeast Asia and 72% in maritime Southeast Asia [1]. To meet growing
food demand, the amount of water used for producing food and fodder crops is expected to
increase further at a rate of 0.7% per year [
3
]. More than 50% of the world’s 271 million ha of
irrigated crop area is located in Asia where rice production accounts for 40–46% of the net
irrigated crop area [
4
].
The spread of irrigation has substantially contributed to increased yields obtained during
the Green Revolution, but the annual growth rates in irrigated area have been very low in
recent decades [
5
]. While water scarcity is aggravating in many countries, it can be anticipated
that competition with other water uses will limit availability of water for irrigated agriculture.
Moreover, climate change will increase uncertainties for obtaining irrigation water when and
where needed [
6
].
Water-saving technologies such as drip and pivot irrigation have been used in upland
(nonflooded) crops, but have limited suitability for paddy rice production. At field level, rice
receives up to 2–3 times more water than other irrigated crops [
7
], but an unknown proportion
of the water losses from individual fields is reused by other fields downstream. Discounting for
this reuse, it can be estimated that irrigated rice receives some 34–43% of the total world’s
irrigation water, or 24–30% of the total world’s freshwater withdrawals [
7
].
However, irrigation water is often used inefficiently and in many cases used in an
unsustainable manner [
8
]. Depending on the actual source of water, irrigation can be classified into (i)
surface irrigation and (ii) groundwater pumping. Many surface irrigation schemes in Asia
consist of decades-old canal infrastructure that are often degraded due to insufficient maintenance
[
9
]. Thus, water supply in many irrigation schemes of Asia is impaired by substantial losses
that accrue between the reservoir or (...truncated)