Multi-scale temporal analysis of actual evaporation on a saline lake in the Atacama Desert

Evaporation is a key component of the water cycle in the endorheic basins of the Chilean Altiplano. In this study, sub-diurnal to climatological temporal changes of evaporation in a high-altitude saline lake ecosystem in the Atacama Desert are analysed. We analyse the evaporation trends over 70 years (1950-2020) at a high-spatial resolution. The method is based on the downscaling of 30-km hourly resolution ERA5 reanalysis data to 0.1-km spatial resolution data using artificial neural networks. This downscaled data is used in the Penman open water evaporation equation, modified to compensate for the energy balance non-closure and the ice cover formation on the lake during the night. Our evaporation estimates show a consistent agreement with eddy-covariance measurements and reveal that evaporation is controlled by different drivers depending on the time scale. At the sub-diurnal scale, mechanical turbulence is the primary driver. At the seasonal scale, more than 70% of the evaporation variability is explained by the radiative contribution term. At interannual scales, evaporation increased by 2.1 mm per year during the entire study period according to global temperature increases. Last, we find that yearly evaporation depends on the El Niño Southern Oscillation (ENSO), where warm and cool ENSO phases are associated with higher evaporation rates and precipitation rates, respectively. Our results show that warm ENSO phases increase evaporation rates by 15%, whereas cold phases decrease by 2%. This investigation contributes with reliable long-term evaporation estimates over a typical saline lake of an arid region and a replicable methodology for climate change assessment and sustainable water management.