Sensitivity of aridity diagnoses to land-atmosphere coupling in South America

Abstract

Land-atmosphere coupling is a key factor for understanding the mean hydroclimatological conditions in South America. Inthis study, we analyzed how land-atmosphere coupling modulates the aridity conditions in the South American continentthrough experiments performed with a regional climate model. We assessed changes in precipitation (P), potential evapora-tion (PET), aridity index (ɸ = PET / P) and vapor pressure deficit (VPD) in experiments with and without soil moisture- atmosphere coupling. Additionally, we analyzed how air dry enthalpy (Hd), moist enthalpy (Hw) and total enthalpy (Ht)change between the coupled and uncoupled experiments, which help to identify patterns in aridity conditions. When ana-lyzing ɸ, we found opposite responses in central-eastern Brazil and southeastern South America (SESA), the two mainhotspots of land-atmosphere coupling. On the other hand, a widespread amplification of VPD is found. Both VPD andenthalpy are locally driven by changes in temperature and water vapor content and reflect wetter conditions in central-eastern Brazil and drier conditions in SESA. Changes in regional circulation, described in previous studies, increasemoisture convergence in Brazil and help to explain the response of each individual metric when coupling is enabled.