Inter-annual variation and influencing factors of irrigation water use efficiency in the hilly and mountainous regions in Southwest China

【Objective】In the hilly and mountainous regions of Southwest China, improving irrigation efficiency is critical due to their complex terrains. This paper studies the inter-annual variation in irrigation water effective utilization coefficient (IWEUC) in these regions and identifies its main influencing factors.【Method】Taking Chongqing in the region as the study area, inter-annual changes in IWEUC were analyzed using data measured across 79 irrigation districts. Nine influencing factors categorized into four groups: natural conditions, resource availability, management practices and engineering infrastructure were selected in the analysis. Principal component analysis (PCA) was used to identify the dominant factors that influence IWEUC. 【Result】 ① IWEUC in Chongqing is lower than the national average due to the difficulty of implementing efficient irrigation in its mountainous terrains. While IWEUC has been growing over time, the growing rate has slowed in recent years. Spatially, IWEUC ranked from highest to lowest as southeast, west, main city and northeast. ② In irrigation districts with similar sizes, pumping-irrigation areas had higher IWEUC than free-flow irrigation areas, likely due to greater transmission efficiency of water in pipelines. However, free-flow irrigation areas showed faster growth in IWEUC. Medium-sized irrigation districts outperformed small-sized ones in absolute IWEUC, yet the latter demonstrated higher growth potential. ③ PCA results showed that areas with water-saving irrigation projects contributed most positively to IWEUC.【Conclusion】To further enhance irrigation efficiency in the mountainous regions of Southwest China, priority should be given to small-scale and free-flow irrigation districts, which have greater potential for improvement. Efforts should focus on improving irrigation management, optimizing water allocation, and expanding water-saving infrastructure, to enhance sustainable agricultural water use in these regions.