Spatiotemporal variations of drainage water and its salinity in the Hetao Irrigation District

【Objective】The Hetao Irrigation District, the largest irrigation district in Inner Mongolia, relies primarily on water diverted from the Yellow River. However, long-term irrigation has led to increasing soil salinization. This study aims to analyze the spatiotemporal variations in drainage volume and mineralization within the district to inform sustainable drainage water reuse strategies.【Method】The analysis was based on drainage water and its mineralization measure from 2006 to 2020 in the irrigation district. The Mann-Kendall trend test was applied to assess the spatiotemporal variations in both drainage volume and mineralization across three irrigation areas: Jiefangzha, Yongji, and Yichang. Additionally, the Spearman correlation coefficient was used to evaluate the relationship between annual drainage volume and mineralization in each area.【Result】From 2006 to 2020, all three irrigation areas exhibited a significant increasing trend in drainage volume. Mineralization levels remained stable in the Jiefangzha area, while both Yongji and Yichang area experienced a significant decrease in mineralization. The Spearman correlation coefficients between annual drainage volume and mineralization were -0.02 for Jiefangzha and -0.81 for both Yongji and Yichang, indicating a strong negative correlation of drainage volume and mineralization in the latter two areas. Monthly data further revealed significant variations in drainage volume and mineralization, generally displaying a negative correlation. Spatially, the highest average annual drainage volume was recorded in Yichang (2.492 hundred million m3), followed by Jiefangzha (1.897 hundred million m3) and Yongji (1.305 hundred million m3). Notably, before 2014, mineralization levels in Yongji and Yichang were higher than those in Jiefangzha; however, this trend reversed after 2014.【Conclusion】Effective reuse of drainage water in the Hetao Irrigation District requires a comprehensive evaluation of both drainage volume and mineralization. Region-specific strategies that consider crop salt tolerance and local soil properties are essential for optimizing the sustainable utilization of drainage resources.