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

PLOS ONE, Dec 2015

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.

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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)


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Andrew Nelson, Reiner Wassmann, Bjoern Ole Sander, Leo Kris Palao. 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, PLOS ONE, 2015, 12, DOI: 10.1371/journal.pone.0145268