Assessment of drought change trends and watershed health using a reliability-resilience-vulnerability framework in mountainous watersheds

Abstract

Quantitative response of climate change impacts to watershed health assessment provides valuable information for management of essential hydrological ecosystem services. Based on this, an integrated and quantitative index was developed using the combination of Reliability, Resilience and Vulnerability (RRV) framework, Standard Precipitation Index (SPI)-RRV and Soil and Water Assessment Tool (SWAT) to assess watershed health trends by considering precipitation anomalies and drought index. The Taleghan mountain watershed in a semi-arid region of Iran was studied for the period 1999–2023 and the future period 2025–2040. The calculation was done for the past and two future emission scenarios, Representative Concentration Pathways (RCPs) 4.5 and 8.5, from the Dynamics Laboratory's Earth System Model 2 M (GFDL-ESM2M) (GCM). The reliability, resilience, vulnerability and SPI-RRV indicators in the health classification of the Taleghan Watershed had normal average values of 0.5, 0.57, 0.59 and 0.5 respectively, indicating a moderate health status. In the future period, average values for reliability, resilience, vulnerability, and SPI-RRV were 0.51, 0.54, 0.27, and 0.44 for RCP4.5, and 0.50, 0.56, 0.24, and 0.43 for RCP8.5. All indicators were classified as moderately healthy, except for the vulnerability index, which was classified as unhealthy. Therefore, the Taleghan Watershed will be more vulnerable to droughts in the future. The reductions in SPI-RRV indicated that the Watershed is not adapted to future droughts. This requires long-term management and conservation planning to sustain water resources. The research methodology is applicable to other regions to determine the health of watersheds in relation to drought.