Irrigation in the North China Plain regulates the diurnal cycle of precipitation and regional water cycle

Abstract

Abstract Irrigation, a significant human activity, impacts regional water cycles and climate. The effect of irrigation on the diurnal cycle of precipitation (DCP) remains ambiguous. In this study, we investigate irrigation's effects on the DCP and assess its contribution to precipitation in North China, utilizing a regional model coupled with a water vapor tracing scheme. Our findings indicate that, during the afternoon, irrigation in the North China Plain (NCP) generates a cooling effect, thereby intensifying the thermal contrast between the mountains and adjacent plain and strengthening the mountain-plains solenoid. As a result, there is an increase in the amount and frequency of afternoon precipitation in the northwestern mountains, while the southeastern plains experience a decrease. The cooling and moistening effects of irrigation inhibit the development of the planetary boundary layer and make it a challenge for air to reach the lifting condensation level, which impedes cloud and precipitation formation, thus delaying the peak of afternoon precipitation. Although irrigation's direct contribution to total precipitation does not exceed 6%, it is responsible for approximately 30% of the total precipitation changes induced by irrigation. The precipitation recycling ratio in the NCP is elevated under irrigation, especially in the mountains, likely due to enhanced moisture and altered local circulations. When the soil moisture is dry, irrigation's positive impact on precipitation is more pronounced, whereas in wet soil conditions, this positive effect diminishes and may even result in reduced precipitation.