Testing a remotely-sensed snow water equivalent product in the framework of the operational European Drought Observatory (EDO)

Winter droughts, defined as periods of reduced precipitation and snow accumulation during the cold season, can have significant impacts on the subsequent summer season, especially over areas that strongly rely on stored water resources released during the spring melting.

The Snow Water Equivalent, SWE, represents a reliable means to quantify the amount of liquid water in the snowpack, and its anomalies can be used to evaluate deviations from the amount usually stored. Unfortunately, the use of SWE for operational monitoring of winter droughts is constrained by the limited availability of long time series of ground observations, and the lack of coordinated measuring networks at European continental scale.

Remote sensing data from microwave sensors, therefore, represent a valuable source of continuously-updated SWE data. Products such as the H-SAF (EUMETSAT Hydrology Satellite Application Facility, http://hsaf.meteoam.it/) SNOBS4-H13 are updated in almost near-real time, providing daily maps covering continental Europe and northern Africa. Limitations include data gaps, difficult retrievals over impervious terrain, coarse spatial resolution and a reduced length of the time series.

In this study, we tested the potential inclusion of a drought indicator based on the H-SAF SWE product in the European Drought Observatory (EDO, http://edo.jrc.ec.europa.eu), with the aim to fill the current gap faced over mountainous basins in terms of early warning of spring water deficits.

An analysis of the full dataset collected between 2013 and 2019 highlights how, currently, the main drawback of the product seems to be represented by the limited length of the time series, as well as by the difficulties to capture snow accumulation over some mountainous areas (e.g., Pyrenees) likely due to the coarse spatial resolution. Spatial aggregation at water basin scale was also tested, in order to evaluate the possibility to reduce the effects of some of these limitations.