Abstract

Introduction: The Sistan Plain, located in southeastern Iran, has a hyper-arid climate and is highly dependent on limited water resources, especially the Himand River. Agriculture has historically been the dominant land use in this region, but in recent years it has experienced severe instability due to a sharp decline in water inflow. This research was conducted with the aim of identifying agriculturally sustainable areas in the Sistan Plain over the period from 1991 to 2021 based on changes in the volume of water entering the region. Considering the drastic reduction in water inflow into the Sistan region, planning for agriculture in the most sustainable areas is essential in order to achieve agricultural sustainability and prevent environmental degradation and financial losses for farmers.

Materials and Methods: This study was carried out in the Sistan Plain, located in the northern part of Sistan and Balouchestan Province. The data used in this research included Landsat satellite images from five time periods (1991, 2000, 2019, 2020, and 2021), Google Earth imagery, field data, and interviews with local residents. The area of water-covered lands in hamoun wetland and the Chahnimeh reservoirs of Sistan was considered as the amount of water entering the Sistan region. Land use and land cover maps were produced at two spatial scales: one covering the entire Sistan region including the hamoun wetland, and another focusing specifically on agricultural lands. These maps were generated using supervised classification of the satellite images into four categories: agricultural land, abandoned land, bare land, and water-covered land. The accuracy of the classifications was assessed using an error matrix and by calculating the Kappa coefficient and overall accuracy.

Results: The findings showed that in 1992 (1371 in the Iranian calendar), more than 280,000 hectares of land in the region were covered by water. However, this area decreased to less than 3,000 hectares in 2000 (1379), indicating a reduction in the inflow of the Helmand River. Similarly, in 1992, the cultivated agricultural land in the region amounted to 98,504 hectares, but by 2000 it had decreased by 31,689 hectares compared to 1992. In 2020 (1399), with the inflow of water from the Helmand River, an area of 102,506 hectares was inundated, and 105,948 hectares were cultivated by farmers. However, in 2021 and 2022 (1400 and 1401), with the complete cutoff of the Helmand River’s flow, only 45,552 and 27,899 hectares, respectively, were cultivated

Discussion: An analysis of land cover maps at a broad scale showed that in 2000, the hamoun wetland had dried up, water-covered areas decreased by 278,800 hectares, and bare land increased to more than 394,000 hectares—clear indicators of the direct consequences of reduced water resources. In 2000, vegetation cover declined from 281,000 to 139,000 hectares on a broad scale. The extent of cultivated lands in 1991 was the highest during the study period, at 98,504 hectares. Despite 2000 being the year with the least water coverage during the study period, the extent of agricultural lands still ranked third, amounting to 66,815 hectares. Results from field interviews and literature reviews showed that most wells in the region contained fresh water. In 2019, following sufficient water inflow, farmers resumed cultivation, and the highest cropping activity since 1991 occurred. With the continued reduction in water from the Helmand River during 2020 and 2021, cultivated land area also declined, and agriculture remained sustainable only in areas near the Chahnimeh reservoirs, where fresh water wells are present. Analysis of maps showing agricultural lands revealed that farmlands—especially those located in western Sistan exhibited the greatest instability during this period and were abandoned as water availability declined.