Reconstructing forest green water fluxes in a Mediterranean region over the past 20 years: Evidence for the drought paradox

Green-water fluxes are a major component of the hydrological cycle globally. According to recent models and experimental observations, during droughts, wetter regions respond by increasing evapotranspiration (ET), while drier regions exhibit decreasing trends due to vegetation water stress. To comprehensively dissect the ET signature of natural forests in a Mediterranean region, typically regarded as a dry environment, in this work, we reconstruct the green-water fluxes of 15 natural unmanaged forests in Central Italy from 2000 to 2022 and explore their dependencies on local temperature and precipitation. Historical ET data are estimated through a time-domain parameterization of the traditional “triangle method”, which leverages satellite imagery to compute actual latent heat flux as a residual term of the land surface energy balance. Based on our results, all forests show a statistically significant increase in Summer ET, and, in warm years, such an increase has occurred in spite of negative precipitation anomaly. These satellite-based observations support the instance of a “drought paradox”, which is not related to temperature nor precipitation anomalies, and probably builds on multi-year temperature and precipitation trends.