University of Birjand Water Harvesting Research 2476-6976 9 1 2026 03 01 Integrated Drought Risk Assessment Using an Entropy-Weighted Fuzzy Index and Copula Functions: A Case Study of Sarbaz River Basin, Iran 96 112 4230 10.22077/jwhr.2026.11758.1208 EN Sahar Maldar Department of Physical Geography, Faculty of Geography and Environmental Planning, University of Sistan and Baluchestan, Zahedan, Iran. 0000-0002-9655-6091 Hamid Nazaripour Department of Physical Geography, Faculty of Geography and Environmental Planning, University of Sistan and Baluchestan, Zahedan, Iran. 0000-0002-9655-6091 Mohsen Hamidianpour Department of Physical Geography, Faculty of Geography and Environmental Planning, University of Sistan and Baluchestan, Zahedan, Iran. 0000-0001-7389-172X Journal Article 2026 07 26 Drought risk assessment based on a reliable, integrated index that encompasses meteorological, hydrological, and agricultural dimensions is critical for understanding future drought trends and for implementing effective prevention and mitigation strategies. This study aims to develop a Multivariate Integrated Drought Index (MIDI) by combining four key drought indicators—Streamflow Drought Index (SDI), Standardized Runoff Index (SRI), Standardized Precipitation Index (SPI), and Standardized Precipitation-Evapotranspiration Index (SPEI)—to enable an objective and holistic evaluation of drought risk. The study area, the Sarbaz River Basin in southeastern Iran, is the region’s only permanent river system and holds strategic importance for agricultural development and unique ecological sustainability, particularly under escalating water scarcity driven by climate change and population growth. The MIDI was constructed using variable fuzzy set theory and the entropy weight method. Drought events were subsequently redefined in terms of duration and severity based on run theory. Copula functions were employed to model the joint probability distribution of drought duration and severity, allowing for a comprehensive assessment of drought risk. Results indicate that the MIDI is well correlated with the time series of individual meteorological and hydrological drought indices and demonstrates greater sensitivity and efficiency in capturing historical drought events compared to single indices. The Sarbaz River Basin has experienced over 100 drought events, with a mean duration of 2.21 months, and 94.6% of the events lasted fewer than five months, indicating that droughts in this basin tend to be of short duration yet occur with high frequency. Droughts of varying severity occur annually across the basin. Given this high frequency, it is recommended that water resource management plans incorporate the MIDI outputs and the joint duration–severity analysis to formulate proactive adaptation strategies. Future research should investigate the influence of climatic variables and land-use changes on drought dynamics within this critical basin. https://jwhr.birjand.ac.ir/article_4230_c0e19ce0dbabbc0d17a4f8d4324cc8e3.pdf