Scenario-based assessment of watershed health under future climate change: a water quantity and quality perspective

Understanding the effects of climate change on watershed health is essential for effective ecosystem management. The main purpose of the current research is to evaluate the health of the Nekarood Watershed in northern Iran using a conceptual model based on reliability (Rel), resilience (Res), and vulnerability (Vul) under various climate change scenarios. Climate data for the periods 2021–2050 and 2051–2080 were simulated using six models under the Shared Socioeconomic Pathways (SSP) scenarios and downscaled with the LARS-WG model. The physically based Soil and Water Assessment Tool (SWAT) model was employed to predict discharge, sediment, nitrate (NO3−), and phosphate (PO43−) under these scenarios. Under baseline conditions, the watershed’s Rel, Res, and Vul indices were 0.46, 0.53, and 0.85, respectively, while the watershed health index (WHI) was 0.59, indicating a moderate status based on high flow discharge, low flow discharge, sediment, NO3−, and PO43− at the watershed outlet. Under the SSP126 scenario, the WHI is projected to change by − 2.7% for 2021–2050 and − 6.6% for 2051–2080. For SSP245, the changes are − 6.1% and + 0.7%; for SSP370, − 5.7% and − 5.0%; and for SSP585, − 3.2% and − 18.7% for the respective future periods. This spatial modeling approach enhances decision-makers’ understanding of temporal changes in the Nekarood Watershed and supports the simulation of climate impacts on land characteristics, including pollutant loads and overall watershed health.