The Validation of Soil Moisture Satellite Products Based on Hydrological Parameters Measured in a Small Basin, Romania

Stated from the idea that soil moisture is correlated with hydrological processes, this study proposed to validated two satellite products: Copernicus Global Land Service’s surface soil moisture at 1 km2 resolution (SSM 1 km) and Copernicus Global Land Service soil water index at 1 km2 resolution (SWI 1 km) taking into account a small basin, located in the west part of Romania, Moneasa representative basin (MRB). The analyses were based on a dataset spanning 2016–2021, which included water discharge, precipitation, evapotranspiration, surface soil moisture, and the soil water index. Based on the Pearson test, the results support the idea that soil moisture is the hydro-pedological parameter that can be analysed based on hydrological elements. The results indicated low correlation between soil moisture and precipitation or soil moisture and evapotranspiration at daily time step, but the aggregated values at 10 days can improve the corrections. The SSM 1 km has closer correlations with the hydrological parameters (streamflow, runoff) than SWI 1 km. The SWI 1 km products have the advantage of generating daily values during April–November from each year, but it has a higher degree of error, especially in forested basins (such as MRB). Overall, the findings emphasise the potential of satellite-derived soil moisture products to complement ground-based observations and enhance hydrological studies, particularly in data-scarce basins.