Controlled drainage, to cope with the adverse impacts of climate change on paddy field's hydrology: a simulation study using the drainmod model, Kunshan, China

A study was carried out to assess the DRAINMOD model in predicting the role of Controlled Drainage strategies and Drain Spacing scenarios in the paddy field. The DRAINMOD model was simulated for the current (2018), Near Future 2021 to 2060 and Far Future 2061 to 2099 in the Kunshan region, China. Potential Evapotranspiration was estimated by the Thornthwaite method. The model performed good agreement in predicting paddy's water balance for the period of 2017-18. Also, Projections of the future climate in the Kunshan region, showed that there will be a decrease in the annual precipitation during rice-growing seasons for both Near Future (2021-2060) and Far Future (2061-2099). The DRAINMOD model was utilized to evaluate the impact of such a future decrease in precipitation on ground Water Tables Depth. Compared to the rice-growing season of 2018, DRAINMOD simulations showed that future Water Table Depths will drop by 38% to 40% for both the Near Future and Far Future under the Representative Concentration Pathway (RCP) 4.5 and RCP 8.5. Such future remarkable drop in Water Table Depths may affect rice yield in the study region. The future water balance in the study area was re-simulated after replacing conventional drainage with Controlled Drainage and an increase in the drain spacing. Simulations revealed that practicing Controlled Drainage and an increase in drain spacing mitigated the future drop in Water Table Depths, thus ensuring better soil moisture conditions for rice. Therefore, Controlled Drainage approaches have the potential to cope with the adverse impacts of climate changes in the paddy fields.