地下水是我国西北干旱半干旱区的重要资源,而大规模的节水改造工程势必造成地下水环境的变化。本文从时空概率分布角度,探索了河套灌区永济灌域节水改造前（1998—2000年）、初期（2001—2006年）、中期（2007—2012年）和后期（2013—2018年）地下水埋深和地下水矿化度的时空变化特征,并运用指示Kriging法分析了节水改造前后不同阈值条件下地下水埋深和矿化度的空间概率分布规律。结果表明：（1） 随着节水改造工程的推进,地下水埋深和矿化度均呈增加趋势,节水改造后期（2013—2018年）较节水改造前（1998—2000年）平均埋深增加了0.36 m,矿化度增加了1.37 g·L^-1。（2） 空间尺度上,节水改造后期33%的浅埋地下水（地下水埋深<2.0 m）高概率区（发生概率在0.5以上）过渡为深埋地下水的高概率区,且受城镇化影响（开采利用量大）,中南部和北部地下水埋深增加显著;矿化度<2.5 g·L^-1和≥3.0 g·L^-1的高概率区分别扩大了17%和4%,即研究区中南部地下水趋于淡化,北部及东西边缘部趋于矿化。（3） 21 a年均深埋地下水（地下水埋深≥2.0 m）高概率区占总面积的39%,主要集中于中南部地区;矿化度<2.5 g·L^-1的高概率区面积占67%,≥3.0 g·L^-1的高概率区面积占比27%且集中分布于北部地区。节水改造增加了地下水埋深（有效降低了地下水位）,虽矿化度呈增加趋势,但矿化地区多集中于各排干附近,建议进一步完善排水系统。

Groundwater is an important resource in the arid region of Northwest China, and large-scale water-saving transformation projects are bound to cause changes in the groundwater environment. On the basis of the spatial-temporal probability distribution, the spatial-temporal variations of groundwater depth and salinity were explored in the Yongji irrigation area of the Hetao Irrigation District before the Agricultural Water-saving Transformation Project (AWSTP) (1998-2000), at the initial stage (2001-2006), the middle stage (2007-2012), and the late stage (2013-2018). The Kriging method was used to analyze the probability distribution of groundwater depth and salinity under different threshold conditions before and after the AWSTP. The results show that as the AWSTP advanced, both the buried depth of groundwater and groundwater salinity increased. In the late stage of the AWSTP (2013-2018), the average buried depth of groundwater increased by 0.36 m, and groundwater salinity increased by 1.37 g·L^-1 compared with preproject measures (1998-2000). On a spatial scale, 33% of the high-probability area of shallow groundwater (i.e., groundwater depth less than 2.0 m; probability of occurrence above 0.5) transitioned to the high-probability area of deep groundwater (i.e., groundwater depth greater than or equal to 2.0 m). Shallow groundwater has been affected by urbanization (with a large amount of groundwater exploitation), and groundwater depth has increased significantly in the central, southern, and northern parts of the area. The high-probability areas of groundwater salinity less than 2.5 g·L^-1 and greater than or equal to 3.0 g·L^-1 have expanded by 17% and 4%, respectively. In other words, the south-central part of the study area tended to desalinate, whereas the northern and eastern edges tended to mineralize. The 21 year average deep groundwater (i.e., groundwater depth greater than or equal to 2.0 m) with high-probability areas accounted for 39% of the total area and is mainly concentrated in the south-central area. The high-probability areas with salinity less than 2.5 g·L^-1 accounted for 67% on average, and the high-probability areas with salinity greater than or equal to 3.0 g·L^-1 were concentrated in the northern region and accounted for 27% of the total area. The AWSTP has resulted in an increase in groundwater depth (i.e., effectively reduced the groundwater level). Although groundwater salinity is increasing, the mineralized areas are mostly concentrated near the drains. Further improvements to the drainage system are recommended.