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Abstract:
The Standardized Precipitation Index (SPI) or the Streamflow Drought Index (SDI), have been widely used to characterize meteorological and hydrological droughts, respectively, in Early-Warning Decision-Making systems (EWDs). However, in high mountain areas, the snow occurrence and evolution play a key role in runoff and water resource availability during spring and summer. “Snow drought” might result in scarcity conditions even though no warning stage is reached regarding drought’s alerts, based on precipitation records. This should be also considered in drought indicators, especially in semiarid mountain regions.
This work addresses some questions on the relationship between snow droughts and their impact on water scarcity (hydrological drought) in several catchments within the Sierra Nevada area in southern Spain: Do precipitation/snow droughts have a similar impact on hydrological droughts? Can the standard drought indexes describe snow droughts and their potential impact on river flow? Following this, both SPI and an Standardized Snowfall Index (SSI, defined as SPI but using snowfall data) are calculated in the study area on different time scales for a reference period of 40 years (1960-2000), together with SDI from the available streamflow time series. The results show the relevant seasonality of snowfall droughts in this area, and the importance of persistent precipitation drought (i.e. duration longer than two years) as antecedent conditions for the impacts of low-snow years on the spring and summer streamflows. Validation during 2001-2021 highlights the need for specific snow drought indexes in the framework of EWSs in high mountain areas in this region.
