Simulating impacts of climate change on cotton yield and water requirement using RZWQM2

Assessing the potential impacts of climate change on cotton (Gossypium hirsutum L.) yield and water demand is crucial in allocating water resources. In this study, cotton yield and water requirement under future climate scenarios was evaluated in Qira oasis, China. Six general circulation models (GCMs), under moderate and high representative concentration pathway (RCP) scenarios (4.5 and 8.5) and elevated CO2 (eCO(2)) concentration (218-502ppm), were used to project climate for near (2041-2060) and far future (2061-2080) periods. With current management practices, the impacts of climate change on cotton yield and water requirement were simulated using the Root Zone Water Quality Model (RZWQM2), which was calibrated with experimental data (2007-2014) in a previous study. For the study region, the GCMs predicted an increase of 2.38 degrees C and 3.24 degrees C in temperature and 3.5% and 5.3% mm in precipitation during the growing seasons (April-October) for 2041-2060 and 2061-2080, respectively. For 2041-2060, seed cotton yield was projected to increase by 0.24Mg ha(-1) (5.6%) under RCP4.5 and 0.19Mg ha(-1) (4.5%) under RCP8.5 comparing to the baseline yield of 4.23Mg ha(-1); however, for 2061-2080, the model predicted a 0.32Mg ha -1 (7.6%) yield increase under RCP4.5 but a 0.28Mg ha(-1) (6.5%) decrease under RCP8.5. The increased cotton yield was mainly attributable to the fertilization effect of eCO(2) dominating the detrimental effects of shorter growing seasons (8.0-9.5 days). Alleviated low temperature stress also slightly promoted cotton yield. Averaged across the RCP4.5 and RCP8.5 scenarios, simulated cropping season water requirement for the 2041-2060 and 2061-2080 were 728mm and 706mm, respectively, an decrease by 7.5% and 10.3% relative to the present day baseline (786mm), respectively. This decrease was attributed to shorter growing seasons and eCO(2). These results suggest that the region's agricultural water crisis may be alleviated in the future.