On the Use of Modis Snow Cover Product for Assessing Snow Extension and Duration Over the Po River Basin

Changes in climatic forcings on the Mediterranean area are foreseen by many global and regional models. Long-term temperature variations are expected to affect snow dynamics, thus impacting on the timing of the hydrologic response in Alpine catchments. Several authors agree in predicting a shift of the hydrologic regime in the major European rivers, due to a changed behavior of mountain valleys. In this context, digital snow maps are a powerful tool for reproducing large-scale snow distribution and extension. The use of such information for hydrological purposes is now considered an outlet of great practical interest. Here, we consider the Snow Covered Area (SCA) Product and develop a procedure for snow detection from MODIS data (MODerate resolution Imaging Spectroradiometeron on board Terra and Aqua satellites). MODIS snow maps have proven to be very reliable, despite the presence of cloudiness can mask the ground, thus preventing any snow detection. An application to Po river basin, in northern Italy, is here proposed. Daily maps of few years (2003-2007) have been analyzed and compared with the Digital Elevation Model (DEM) of the study area. By some clear-sky days we got complete maps of snow areas throughout the seasons, reproducing large-scale snow cover duration and its dependence on altitude. Focusing on the issue of cloudiness, we highlighted its increase at higher elevation. From our point of view, after this first attempt, MODIS Snow Products seem to have great applicative potentiality. However, many applications are conditioned to the possibility of providing a reliable estimation of ground conditions beneath the clouds