Investigating the Different Hydrological Components Influenced by Climate Change and Land Use Change Scenarios in the Pasikhan Watershed and Their Impact on the Anzali Wetland

Without hydrological models the investigation and management of watersheds can be time-consuming and costly. This study aims to explore various hydrological factors including runoff, sedimentation, evaporation, and transpiration in Pasikhan watershed located in Guilan province. The study also examines the impact of these factors on the Anzali Wetland. To achieve this, the research utilizes the SWAT model. Data on flow discharge, precipitation, and sedimentation for three hydrometric station in the Pasikhan watershed from 1999 to 2020 were obtained from the regional water company of Guilan province. The necessary maps for model execution were obtained using established methods. Predictions for various factors, such as flow rate, sedimentation, surface runoff, evaporation and transpiration, deep aquifer recharge, curve number, deep infiltration, and watershed runoff, were made for the years 2040 and 2071. Discharge-sediment from 1999 to 2011 is used for calibration and for validation used the data from 2012 to 2022 is used. The study also assessed changes in hydrological components caused by climate change using the RCP8.5 scenario and land use changes. The findings demonstrate variations in multiple hydrological elements and precipitation patterns within the catchment basin. The Nash Sutcliffe criterion yielded values between 0.60 and 0.80 for both the calibration and validation phases of the model in terms of flow rate and sedimentation. This indicated that the implementation of the SWAT model is satisfactorily accurate. Results showed that the maximum surface runoff within the basin will reach 485 mm in 2055, coinciding with a rainfall of 1431 mm. Additionally, the study identified the highest levels of evaporation and transpiration as 1707 mm within the RCP8.5 scenarios in 1996. Overall, the research emphasizes the negative impact of sediment generated within the Pasikhan watershed on the Anzali Wetland, highlighting the need for effective control measures to mitigate wetland degradation