A Copernicus-based evapotranspiration dataset at 100-m spatial resolution over the Mediterranean region

Abstract

Abstract. Evapotranspiration (ET) is responsible for regulating the hydrological cycle with a relevant impact on air humidity and precipitation, particularly important in the context of acute drought events in recent years. With the intensification of rainfall deficits and extreme heat events, the Mediterranean region requires regular monitoring to enhance water resources management. Even though remote sensing provides spatially continuous information for estimating ET on large scales, existing global products with spatial resolution ≥ 0.5 km are insufficient to capture spatial detail at a local level. In the framework of the ESA 4DMed-Hydrology project, we generate an ET dataset at both high spatial and temporal resolutions by the Priestley-Taylor Two-Source Energy Balance model (TSEB-PT) driven by Copernicus satellite data. We build an automatic workflow to generate 100-m ET product by combining data from Sentinel-2 (S2) MSI and Sentinel-3 (S3) land surface temperature (LST) with ERA5 climate reanalysis derived within the period 2017–2021 over four Mediterranean basins in Italy, Spain, France, and Tunisia (Po, Ebro, Hérault, Medjerda). First, original S2 data are pre-processed before deriving 100-m inputs for the ET estimation. Next, biophysical variables, like leaf area index, and fractional vegetation cover are generated, and then they are temporally composted within a 10-day window according to Sentinel-3 acquisitions. Consequently, decadal S2 mosaics are used to derive the remaining TSEB inputs. In parallel, we sharpen 1-km S3 by exploiting dependency between coarse-resolution LST and 100-m S2 reflectances using the decision trees algorithm. Afterward, climate forcings are utilized for modeling energy fluxes, and next for daily ET retrieval. The daily ET composites demonstrate reasonable TSEB-PT estimates. Based on the validation results against eight Eddy Covariance (EC) towers between 2017–2021, the model predicts 100-m ET with an average root mean square error of 1.38 mm day-1 and Pearson coefficient equal to 0.60. Regardless of some constraints, mostly related to the high complexity of EC sites, TSEB-PT can effectively estimate 100-m ET, which opens up new opportunities for monitoring the hydrological cycle on a regional scale. The full dataset is freely available at https://doi.org/10.48784/b90a02d6-5d13-4acd-b11c-99a0d381ca9a, https://doi.org/10.48784/fb631817-189f-4b57-af6a-38cef217bad3, https://doi.org/10.48784/70cd192c-0d46-4811-ad1d-51a09734a2e9, and https://doi.org/10.48784/7abdbd94-ddfe-48df-ab09-341ad2f52e47 for Ebro, Hérault, Medjerda, and Po catchments, respectively (Bartkowiak et al., 2023a–d).