An Atlantic influence on evapotranspiration in the Orinoco and Amazon basins

Tropical South America's hydroclimate is influenced by ocean-atmospheric variability modes (drivers of climate variability). It is still not known which physical mechanisms teleconnect the Atlantic modes of variability with South America's soil moisture, net radiation, and terrestrial evaporation (evapotranspiration). Understanding these mechanisms is essential to predict the response of ecosystems. This study uses composites of reanalysis and satellite data to identify the processes linking land-surface anomalies and ocean-atmospheric modes. It estimates the control soil moisture and net radiation impose on evapotranspiration (categorised as water- or energy-limited regimes). It shows that these two local controllers of evapotranspiration are influenced by the position of the Intertropical Convergence Zone (ITCZ). However, the evapotranspiration anomalies are driven by the phase of each climate mode, which alter water and radiation availability. The Atlantic Meridional Mode (AMM) generates cross-equatorial wind anomalies that affect moisture convergence, which in turn modify the cloud cover, precipitation, soil moisture, radiation availability, and hence evapotranspiration. The anomalies have important geographical differences depending on the season analysed; they migrate from the east in austral autumn towards the central Amazon and western Orinoco in austral spring. The Atlantic Niño Equatorial mode (Atl3) affects evapotranspiration in the Guianas and eastern Orinoco by means of pressure and trade wind variability, which in turn affect local hydrometeorological conditions and evapotranspiration. Both Atlantic modes mainly impact regions different from those impacted by El Niño-Southern Oscillation (ENSO), although northeast Brazil and the Guianas might experience overlapping effects. Therefore, these ocean-atmospheric modes impact the water, energy, and carbon cycles; they might influence regional climate extremes (e.g. droughts and floods); and they are critical for achieving sustainable development goals (SDGs).