Potentialities of Sentinel-2 images for the study of the fresh water resource in a mountainous catchment

Water quality and availability are nowadays essential requirements for all those activities that need an exploitation of the water resource: e.g. potable use, hydroelectricity production, agriculture, recreation. Inland water originates from atmospheric events and is stored in solid state as glaciers or snow (e.g. on the mountains) or in natural and artificial lakes at any altitude. The well documented climate warming has, among its multiple effects, the modification of the equilibrium between liquid and solid phase of water, its storage and availability, as well as changes in the precipitation regime, such as the reduction and intensification of rainfall events alternated to long aridity periods. All these changes alter water quality and water availability at catchment level. We are experimenting the use of earth observation data (Sentinel-2) to track temporal variations of land covers, lake surface and lake water colour over the last 5 years in a small high-altitude catchment in Italy (e.g. Lake Ceresole watershed, Orco Valley, Piedmont). Here, satellite derived data (e.g. snow cover and water colour), coupled with available meteorological data (e.g. precipitation), are analysed in order to find possible correlations between water colour and snow melting, or water colour changes following strong or extreme meteorological events. Water colour is a largely recognised proxy of water quality. In particular, in mountainous environments, where the anthropic pressure is minimized and natural processes are prevailing, water colour is mainly driven by the presence of solid sediments inside the water. These sediments can be released due to the melting of snow and ice, particularly during thaw periods, thus at seasonal timescale, with possible variations among different years (these variations due to particular meteorological conditions relative to each single year). Also, solid transport as river flow or runoff, can be generated as a consequence of heavy rainfall events, and those sediments can reach the lakes within the catchment modifying their water colour. With this study, we would like to understand if the high spatial resolution of Sentinel-2 acquisitions (i.e. 10m) and its revisit time (2-5 days), except for the drawbacks of all optical satellite sensors (e.g. cloud cover), can provide useful information to follow the on-going modifications that the mountainous environment is facing due to the global warming. The use of earth observation data for this purpose would be a valuable tool in helping both monitoring and understanding of climate change consequences, and in managing the water resource in places not easily accessible for periodic in-situ measures. In fact, mountains represent both the ideal location where nature responds to climatic pressures, but also, they constitute the water sink of fresh water for downstream valleys.