Satellite monitoring of the timing and extent of dry conditions in the Tagliamento River

In recent years, many rivers have experienced an increase in periods of total absence of surface runoff, a phenomenon attributed both to climate change and intensive use of water resources. Approaches based on the use of multispectral satellite images from the Landsat and Sentinel-2 missions are emerging to address the limitations of traditional measurement tools, which provide only point measurements and are sparsely distributed across the minor hydrological network. The use of false-color images, obtained by combining the SWIR, NIR, and RED multispectral bands, has allowed for distinguishing water from other land covers in river corridors. The application of a semi-automatic method, based on the analysis of reflectance in the NIR band, enabled the measurement of the length of dry stretches and its evolution over time. The analysis, conducted over a 40-year period along a 6 km stretch of the Tagliamento River in Friuli-Venezia Giulia, revealed significant trends in the increase of dry conditions. Specifically, greater longitudinal discontinuity of the flow and an increase in the total length of dry conditions were observed during the winter months.