Simulation of response of water requirement for rice irrigation to climate change

The climate change will cause the alteration of the processes of crop water consumption, and thus affect the irrigation water requirement. As one of the most important crops in China, rice accounts for 18% of the country's total cultivated area. Therefore, understanding the impacts of climate change on rice water consumption is of great significance. Investigations on response of rice irrigation water requirements to climate change are beneficial to develop adaptation strategies to climate change and thus ensure food security and the sustainable use of water resources. In this study, changes in rice yield and irrigation water requirements in the past five decades (1961-2010) under flood irrigation and intermittent irrigation were investigated using rice model ORYZA2000 based on historical meteorological data. The rice model ORYZA2000 genetic parameters were calibrated and validated using two calibration programs, DRATES and PARAM, built in the ORYZA2000 model based on two years farm experiment data in Kunshan Station. The potential impacts of future climate change on the rice yield and irrigation water requirements were also examined using validated rice model ORYZA2000. Climate data in the future were generated by the HadCM3 (Hadley Centre Coupled Model version 3) of the IPCC 3rd Assessment Report under A2 and B2 emission scenarios. Statistical downscaling method (SDSM) was employed in this study to get future input meteorological data (2011-2099) (including precipitation, daily air temperature, vapor pressure, wind speed, and radiation data) in Kunshan station of the rice model ORYZA2000. Daily NCEP/NCAR reanalysis data sets during the period of 1961-2001 were used to calibrate and validate the SDSM model. The results indicated ORYZA2000 model can be used to simulate the rice index in a relative high accuracy, and thus can be used to conduct the climate change impact assessment. The SDSM performed generally well in reproducing daily meteorological data for input of rice model ORYZA2000. The simulation of changes in related variables during historical period indicated the significant increases in rice water consumption were found during the past decades. However, rice water irrigation requirements and yield present significant decreasing trends because of increasing precipitation and shorten growth duration caused by increasing air temperature and decreasing radiation, respectively. The rice water consumption will increase under both intermittent irrigation and flood irrigation in the future. Irritation water requirements will decrease significantly due to increasing precipitation and rice water consumption in the future. Compared with that in the baseline, the rice yield will experience decrease and the decrease magnitudes will be enlarged over time due to the negative effect from increasing air temperature.