How Will Climate Change Impact Water Consumption for Rice Irrigation in Southern Brazil?

Abstract:

Globally, agricultural water use accounts for most of the water that is withdrawn from surface water and groundwater. Rice, one of the world's leading food crops, requires that fields be continuously flooded to obtain optimal yields. High air temperature and consecutive rainless days in rice-growing areas can significantly reduce rice yields, leading to food scarcity. Climate change is expected to affect water demand for rice via changes in rainfall regime, soil water balance, and evapotranspiration. Higher temperatures and increased variability of precipitation are predicted to increase water demand and could potentially require more irrigation in lowland rice-growing areas. In this study we present the first results from model simulations in which we integrated a rice model into the Agro-IBIS dynamic ecosystem model. We predict the impact of climate change on the water use requirement of rice production in southern Brazil and evaluate changes in irrigation needed to meet minimum water demand to sustain current yields. Brazil is the 9^th top rice producer in the world, and southern Brazil accounts for about 80% of the national production. The Agro-IBIS model was driven with historic weather data provided by CRU (1961-90) and with two future climate scenarios from the Coupled Model Intercomparison Project Phase 5 (CMIP5) for 2015-2100 – Representative Concentration Pathways 4.5 (RCP45) and 8.5 (RCP85). On an hourly time step, Agro-IBIS accounts for gains (precipitation) and losses (evaporation, transpiration, infiltration and runoff) of water in each grid cell, and uses rules to irrigate in order to maintain a specific height of standing water on the field. Simulated historic and future amounts of irrigated water needed to maintain this water height will be evaluated to predict future water demand for rice production in southern Brazil.