Modeled effects of irrigation on surface climate in the Heihe River Basin, Northwest China

In Northwest China, water originates from the mountain area and is largely used for irrigation agriculture in the middle reaches. This study investigates the local and remote impact of irrigation on regional climate in the Heihe River Basin, the second largest inland river basin in Northwest China. An irrigation scheme was developed and incorporated into the Weather Research and Forecasting (WRF) model with the Noah‐MP land surface scheme (WRF/Noah‐MP). The effects of irrigation is assessed by comparing the model simulations with and without consideration of irrigation (hereafter, IRRG and NATU simulations, respectively) for five growth seasons (May to September) from 2009 to 2013. As consequences of irrigation, daily mean temperature decreased by ~1.7°C and humidity increased by ~2.3 g kg−1(corresponding to ~38.5%) over irrigated area. The temperature and humidity of IRRG simulation matched well with the observations, whereas NATU simulation overestimated temperature and underestimated humidity over irrigated area. The effects on temperature and humidity are generally small outside the irrigated area. The cooling and wetting effects have opposing impacts on convective precipitation, resulting in a negligible change in localized precipitation over irrigated area. However, irrigation may induce water vapor convergence and enhance precipitation remotely in the southeastern portion of the Heihe River Basin. A new irrigation parameterization scheme mimicking the local irrigation activities was incorporated into WRF/Noah‐MP modelThe irrigation results in strongly cooling and wetting effects on surface, and hence, modeling warm and dry bias are largely reducedThe irrigation has not modified local precipitation while has remotely precipitation effects by modifying atmospheric moisture transportation