DRAINMOD simulation of paddy field drainage strategies and adaptation to future climate change in lower reaches of the Yangtze river basin

The DRAINMOD model was used to simulate the current and future water balance in the Yanyun Irrigation District, China. Projections of future climate in the district (2021:2050) show that annual maximum and minimum temperatures will increase by [1.09 and 1.15 degrees C] under the representative concentration pathway RCP4.5 and [1.34 and 1.39 degrees C] under RCP8.5, besides more frequency of one-day peak precipitation events. DRAINMOD simulations revealed that future annual runoff will increase by 33.3% (RCP4.5) and 36.9% (RCP8.5), while groundwater tables will drop by 6% (RCP4.5) and 14.5% (RCP8.5). Future hydrology has been resimulated, but with increasing the capacity of surface depressions in an attempt to minimize adverse impacts of climate change, and results have been checked twice: under proper and improper subsurface drainage practices. Under proper subsurface drainage practices, it was revealed that future runoff will decrease by 25.3% (RCP4.5) and 23.6% (RCP8.5), which will cause a rise in groundwater tables to desired levels, while in contrast, improper subsurface drainage practices will increase future runoff by 13.7% (RCP4.5) and 2.8% (RCP8.5), all compared to future values before adaptation. Therefore, proper drainage strategies are a vital tool that helps to cope with climate change in agricultural lands and mitigate future runoff rates.