Does snow storage affect the Palmer drought severity index? Revisiting PDSI drought indicator via conceptual model and large-scale information

Climate change and its impacts have significantly altered the hydro-climatological conditions worldwide. Accurate monitoring of drought is a crucial work for assessing water availability and environmental suitability. The Palmer Drought Severity Index (PDSI) is a key indicator used to measure hydrological drought. However, its application in mountainous and snow-covered regions is limited due to the indicator's inadequate representation of snow hydrology and its impact during spring and summer. In this research, the authors aimed to enhance the PDSI drought indicator by incorporating snow storage and snowmelt processes via conceptual approach and large-scale snow information. Four different scenarios were developed and tested in the Gheshlagh watershed, a mountainous basin in western Iran. To ensure a comprehensive analysis, the Standardized Precipitation Index (SPI) was also employed to evaluate the results. Additionally, an alternative water balance model, better suited for the watershed, was used in place of the Palmer two-soil-layer water balance model. While the simulated indicators showed good agreement with the benchmark PDSI model, the results revealed significant changes in drought indicators, particularly during summer and spring, when considering snow storage. Moreover, the impact of using a different water balance model was found to be more influential than incorporating snow storage in the PDSI framework. Based on the findings, the authors recommend revisiting the PDSI approach by incorporating region-specific water balance models and accounting for the effects of snow storage.