A health index for surface water resources during drought: an automated fuzzy-based performance criteria approach

A new framework has been developed to assess the health of surface water resources in a basin, integrating a modified Multivariate Standardized Runoff Index with the concepts of reliability, resiliency, and vulnerability, using both traditional (fixed) and fuzzy approaches. This framework has been applied to the upstream sub-basin of the Zayandehrud Dam, Isfahan, Iran, for both the historical period (1990–2018) and future projections (2025–2053) under three emission scenarios: SSP1-2.6, SSP2-4.5, and SSP5-8.5. Also, a method was developed to automatic regulation of parameters the fuzzy membership function based on the real drought conditions of the basin. The main results revealed that (1) superior performance of the automated fuzzy approach in identifying drought intensity, making it more effective than the fixed approach in quantifying the health of the basin’s surface water resources under drought conditions; (2) the number of drought events and the mean drought intensity will be higher in the future periods than those in the historical one; (3) In the fixed approach, reliability, resiliency, and vulnerability values were estimated to be lower for the historical period than for the future period. Conversely, in the fuzzy approach, reliability and vulnerability values were comparable across both historical and future periods, while resiliency was estimated to be higher in the future period; and (4) classification of the basin’s health under drought conditions as "unhealthy" using the fixed approach for historical and future periods, compared to "moderate healthy" classification using the automated fuzzy approach for both periods.