Spatiotemporal Heterogeneity of Long-Term Irrigation Effects on Drought in China’s Arid and Humid Regions

Analyzing the spatiotemporal characteristics of meteorological droughts (MD) and agricultural droughts (AD) and their propagation in different climate zones is important for effective drought management, climate adaptation, and food security. This study takes a unique approach by comparing irrigated and rainfed croplands. A comprehensive framework is developed using drought indices, statistical analysis, trend tests, and wavelet transforms. The spatiotemporal evolution patterns, trends, and correlations of MD and AD in Xinjiang and the Middle-lower Yangtze Plain (MYP) are investigated. The main results showed that severe MD events (e.g., Xinjiang 2005–2009 and MYP 2004–2009) significantly impacted rainfed agricultural systems, leading to a decline in vegetation condition. Long-term irrigation can substantially alleviate AD under MD conditions. From 2000 to 2019, AD on irrigated croplands in Xinjiang continuously improved, while rainfed croplands deteriorated significantly during MD events. In contrast, although overall AD in MYP was mitigated, the benefits of irrigation were only evident during severe AD periods and weakened after 2013. Correlation and wavelet analyses revealed different drought propagation mechanisms between irrigated and rainfed croplands, highlighting the key role of local climate conditions and spatial heterogeneity in determining irrigation efficiency. The findings provide important guidance for optimizing drought management strategies, agricultural planning, and sustainable water resource management.