RESEARCH ARTICLE Climate-Determined Suitability of the Water Saving Technology "Alternate Wetting and Drying " in Rice Systems: A Scalable Methodology demonstrated for a Province in

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 pro-portion 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) tech-nique 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 infor-mation on rice area, rice seasonality, rainfall, potential evapotranspiration and soil percola-tion rates to assess the suitable area per season. We apply the model to Cagayan provinc