Introduction and Purpose: Understanding how river basins respond to climate variability and land-use change is essential for sustainable water resource management, especially in semi-arid regions. In recent decades, climate and land-use change have increasingly altered runoff generation, flow timing, low-flow behavior, and water availability for ecosystems. The Kashafrud River Basin (KRB) in northeastern Iran represents an important semi-arid basin. Despite their importance, integrated basin scale assessments of hydro-climatic trends, land-use dynamics, and flow-regime alteration remain limited. Therefore, this study aimed to provide a comprehensive assessment of the combined effects of climate variability and land-use change on the hydrological regime of the KRB over the period 1973–2023. The specific objectives were to examine long-term trends and abrupt changes in precipitation, temperature, and streamflow; quantify spatiotemporal land-use dynamics; and evaluate alterations in the river flow regime using hydrological alteration indicators.

Materials and Methods: The study was conducted in the KRB, located in northeastern Iran. Long term hydro-climatic conditions were assessed over five decades, from 1973 to 2023, using precipitation, temperature, and streamflow data. To identify temporal trends and quantify their magnitude, the Mann-Kendall trend test and Sen’s slope estimator were applied. Abrupt changes in hydro-climatic time series were detected using Pettitt’s test. Land-use dynamics were mapped for six reference years: 1973, 1983, 1993, 2003, 2013, and 2023, using Google Earth Engine. In addition, the Indicators of Hydrologic Alteration framework was employed to evaluate changes in the streamflow regime. This framework was used to assess hydrological changes in flow magnitude, timing, frequency, and variability.

Results and Discussion: The results revealed substantial hydro-climatic, land-surface, and streamflow alterations in the KRB during 1973-2023. Precipitation exhibited a considerable declining tendency, with the most pronounced reductions observed at upstream stations. In contrast, temperature showed a continuous increasing trend across all stations, indicating persistent warming throughout the basin. These climatic changes suggest increasing stress on the basin’s water balance and reduced water availability. The land-use analysis demonstrated marked landscape transformation over the five-decade period, particularly through urban expansion and agricultural growth. These changes are hydrologically important because land-use and surface characteristics affect infiltration, runoff generation, evapotranspiration, groundwater recharge, and streamflow response. The hydrological alteration analysis showed that the natural flow regime of the river has been disrupted. The main flow-regime changes included reduced low-flow conditions, shifts in peak-flow timing, and increased flow variability. These alterations show that the hydrological behavior of the Kashafrud River has changed in flow quantity, timing, and variability, all of which are critical components of ecological flow regimes. The results suggest that the observed streamflow changes cannot be explained by a single driver. Rather, they reflect the dynamic and synergistic interaction between climate variability and land-use transformation. Declining precipitation, continuous warming, urban development, and agricultural expansion have collectively modified the magnitude, timing, and variability of streamflow. This interaction has disrupted the natural flow regime and increased ecological and water-security challenges in the basin.

Conclusion: This study shows that the KRB has undergone significant hydro-ecological alteration over the past five decades. The combined effects of decreasing precipitation, increasing temperature, urban expansion, and agricultural growth have substantially modified the basin’s hydrological regime, leading to reduced low-flow conditions, shifts in peak-flow timing, and greater flow variability. These findings indicate that climate variability and land-use change have interacted to disrupt the natural streamflow regime, with important implications for ecological integrity and water security. The study underscores the need for adaptive and integrated land and water management in the KRB. Sustainable land and water management, conservation agriculture, and improved water governance are necessary to enhance the resilience of this semi-arid basin under continuing environmental change. The findings also show the value of combining remote sensing, statistical tests, and hydrological alteration indicators to identify long-term hydrological shifts, transition points, and ecological implications in river basins affected by climate and land-use change.