Modeling the Climate Change Adaptation of Crop Production using Irrigation over Water-Limited Region

Monday, 15 December 2014
Masashi Okada1, Toshichika Iizumi1, Gen Sakurai1, Toru Sakai1 and Masayuki Yokozawa2, (1)NIAES National Institute for Agro-Environmental Sciences, Tsukuba, Japan, (2)Shizuoka University, Shizuoka, Japan
Replacing rainfed cropping system by irrigated one is assumed to be an effective measure for climate change adaptation in agriculture. However, in many agricultural impact assessments, future irrigation scenarios are externally given and do not consider the space-time varying available agricultural water under changing climate and land use. For these reason, this study aimed to (1) develop a crop-river coupled model that can simultaneously simulate crop growth and yield over a river watershed, river discharge and their dynamic interactions by embedded a large-area crop model, PRYSBI-2 [Sakurai et al., 2014] into a hydrologic model, H08 [Hanasaki et al., 2008]; (2) apply the developed coupled model to the Songhua River watershed in Northeast China and evaluate the model’s performance by comparing the historical model simulations outputs; (3) assess the effects of adaption measure expanding irrigated area under climate change. The modeled year-to-year variations in soil moisture were comparable to the reference with the Pearson’s correlation coefficient (r) of 0.75 (p<0.001) and root-mean-square error (RMSE) of 13 %. The modeled river discharge accurately matched with the observation data with the r of 0.83 (p<0.01) and RMSE of 22 %. And the modeled soybean yields were quantitatively comparable to the reference with the r of 0.66 (p<0.001) and RMSE of 21 %. We made simulations to project the changes of potential soybean production under climate change scenarios and irrigation area expanding scenarios. It was projected that the soybean production effectively increase until the irrigated area has been increased 5 times compared to around the year 2000. However, the more increase in the irrigated area would bring significant reduction of the increase rate in soybean production due to depletion of available agricultural water resources.