Document Type : Original Article
Subjects
1. Introduction
Climate change and land use modifications represent two of the most pressing environmental challenges of the 21st century, with significant implications for hydrological systems. Semi-arid regions like the Kahneh Joghatai watershed in Razavi Khorasan Province are particularly vulnerable due to their delicate ecological balance and dependence on seasonal precipitation patterns. These areas face compounded risks from increasing temperatures, altered rainfall distribution, and changing land cover characteristics, which collectively influence runoff generation, soil erosion rates, and water resource availability. Understanding these dynamics is crucial for developing effective water management strategies in water-stressed environments. This study examines the integrated effects of climate change and land use alterations on runoff generation patterns, providing critical insights for sustainable watershed management in semi-arid regions.
2. Materials and methods
The research employed the Soil Conservation Service Curve Number method, a widely recognized hydrological model for runoff estimation. The Soil Conservation Service (SCS) method, developed by the U.S. Department of Agriculture, is a simple yet effective hydrological model for estimating surface runoff from rainfall. It uses a Curve Number (CN) that reflects soil type, land cover, and moisture conditions. Higher CN values indicate greater runoff potential. The method is particularly useful for data-scarce regions and is widely applied in watershed management, flood control, and land-use planning. Its empirical approach balances accuracy with practicality, making it a popular tool in hydrological studies. The study area was divided into eight distinct sub-watersheds using GIS-based watershed delineation techniques. Hydrological data, including a 72 mm rainfall event over 24 hours, served as the baseline for analysis, complemented by land cover classification from satellite imagery and topographical data. Climate projections were derived from the HadGEM3-GC31-LL model for two representative scenarios (SSP245 and SSP585) covering the period 2024-2050. The SSP245 and SSP585 scenarios represent the latest climate change pathways within the IPCC (AR6) framework, modeling different socioeconomic development and greenhouse gas emission trajectories. The SSP245 scenario, known as the intermediate pathway, reflects moderate greenhouse gas emissions and is projected to result in approximately 2-3°C of global warming by the end of this century. This scenario incorporates a combination of climate policies and the development of low-carbon technologies. In contrast, the SSP585 scenario represents the most pessimistic high-emissions pathway, forecasting 4-5°C of global warming by 2100 under conditions of continued heavy reliance on fossil fuels and rapid economic growth without environmental considerations. These scenarios serve as critical tools for understanding potential climate futures under varying human development choices and mitigation efforts. The methodology incorporated spatial analysis in ArcGIS, statistical evaluation of runoff patterns, and climate scenario modeling to assess future hydrological changes.
3. Results and Discussion
The analysis revealed significant spatial variability in runoff generation across the watershed. Sub-watershed K3 exhibited the maximum runoff of 65.5 mm, attributable to its steep slopes and low permeability characteristics, while K7 showed the minimum runoff of 30.5 mm due to its better vegetation cover. The total watershed runoff reached 359.2 mm, equivalent to approximately 6 million cubic meters of water. Climate projections indicated a concerning 12-18% reduction in mean annual precipitation by 2050, coupled with a 23% increase in rainfall intensity. These changes suggest a future scenario of more extreme hydrological events, with longer dry periods interrupted by intense precipitation episodes. The findings align with global observations of climate change impacts on semi-arid regions, highlighting the need for adaptive water management strategies that account for both increased flood risks and overall water scarcity.
4. Conclusion
This study demonstrates the significant impacts of climate change and land use modifications on hydrological processes in the Kahneh Joghatai watershed. The projected reduction in precipitation, combined with increased rainfall intensity, presents a dual challenge for water resource management in this semi-arid region. The spatial variability in runoff generation underscores the importance of sub-watershed-specific management approaches. These findings emphasize the urgent need for integrated water resource management strategies that incorporate climate adaptation measures, including improved water storage capacity, enhanced vegetation cover, and flood preparedness systems. The research provides a scientific basis for policymakers to develop targeted interventions that address both current water management challenges and future climate scenarios.
5. Acknowledgment & Funding
The authors gratefully acknowledge the support provided by Hakim Sabzevari University for facilitating this research. Special thanks are extended to the technical staff who assisted with data collection and analysis.
6. Conflict of Interest
The authors declare no competing financial interests or personal relationships that could have influenced the work reported in this paper. All data were collected and analyzed objectively, without bias from any external parties.
