Many river basins are facing a reduction of flows which might be attributed to changes in climate and human activities. This issue is very important in transboundary river basins, where already existing conflicts about shared water resources between riparian countries can easily escalate. The decrease of streamflow in the transboundary Hirmand (Helmand) River is one of the main challenges for water resources management in Iran and Afghanistan. This research aims to quantify the causes of this problem which has a direct impact on the dryness of the Hamoun wetlands being an international Ramsar site. To achieve this, the land use changes in the Middle Helmand Basin (MHB) in Afghanistan were evaluated for three time periods between 1990 and 2011 using remote sensing data and the Soil and Water Assessment Tool (SWAT) Model for understanding watershed response to environmental changes. It was concluded that the total irrigated area in the region has increased from 103,000 ha in 1990 to 122,000 ha in 2001 and 167,000 ha in 2011 (62% increase). According to the results, the average annual discharge when adapting the land use during the simulations was 4,787 million cubic meters (MCM)/year and while employing the land use of 1990 from the beginning of the simulations, the average annual discharge was 5,133 MCM/year. Therefore, the agricultural developments in the Helmand basin decreased the discharge with about 346 MCM/year accompanying an increase of 64,000 ha in an irrigated area in MHB after 1990. Notably, the impact of land use change increases significantly for more recent periods and causes a reduction of 810 MCM in annual streamflow for the MHB. The amount of water depletion (i.e. actual evapotranspiration) per hectare has increased from 5,690 in 1985 to 7,320 m³ in 2012. The applied methodology of this study is useful to cope with such a data scarcity region. It can help quantify the impact of land use change on the region and formulates strategies that can improve the situation between Iran and Afghanistan.

许多流域面临的流量减少可能归因于气候和人类活动的变化。这个问题在跨境流域非常重要，在沿岸国家之间已经存在的关于共享水资源的冲突很容易升级。跨界希尔曼德河（赫尔曼德河）的水流量减少是伊朗和阿富汗水资源管理的主要挑战之一。这项研究旨在量化此问题的原因，该问题直接影响作为国际拉姆萨尔（Ramsar）站点的哈蒙湿地的干旱。为了达成这个，运用遥感数据和土壤和水评估工具（SWAT）模型对阿富汗中赫尔曼德盆地（MHB）的土地利用变化进行了1990年至2011年的三个时间段评估，以了解流域对环境变化的响应。结论是该区域的灌溉面积从1990年的103,000公顷增加到2001年的122,000公顷和2011年的167,000公顷（增加了62％）。根据结果​​，在模拟过程中调整土地利用时的年平均排放量为47.87亿立方米/年，而从模拟开始就采用1990年的土地使用量时，年平均排放量为5133 MCM /年。年。因此，赫尔曼德河流域的农业发展减少了排放量，每年约346 MCM，增加了64 MCM，1990年之后，在MHB的灌溉区域中有000公顷。值得注意的是，土地使用变化的影响在最近时期显着增加，并导致MHB的年流量减少810 MCM。每公顷的耗水量（即实际蒸散量）从1985年的5,690增加到7,320 m³，2012年本研究的应用的方法是有用的，以应付这样的数据缺乏区域。它可以帮助量化土地利用变化对该地区的影响，并制定可以改善伊朗与阿富汗之间局势的战略。