Evapotranspiration trends and variability in southeastern South America: The roles of land‐cover change and precipitation variability

• Published in: International journal of climatology Vol. 42; no. 4; pp. 2019 - 2038
• Main Authors: Ruscica, Romina C., Sörensson, Anna A., Diaz, Leandro B., Vera, Carolina, Castro, Aline, Papastefanou, Phillip, Rammig, Anja, Rezende, Luiz F. C., Sakschewski, Boris, Thonicke, Kirsten, Viovy, Nicolas, Randow, Celso
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 30.03.2022; Wiley Subscription Services, Inc; Wiley
• Subjects: Anomalies; Atmospheric models; Continental interfaces, environment; Convergence zones; Dipoles; dynamic global vegetation models; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; Evapotranspiration; Evapotranspiration trends; La Nina; Land cover; land‐cover change; Ocean, Atmosphere; Precipitation; Precipitation variability; Sciences of the Universe; Seasonal variability; Seasonal variations; South America; South Atlantic Convergence Zone (SACZ); Southern Oscillation; subtropical dipole; Summer; summer variability and trends; Trends; Variability; Vegetation; South America; South America climate; Land-cover changes; Precipitation variability; Evapotranspiration; Vegetation models; Dipole evolution; Trends analysis
• ISSN: 0899-8418; 1097-0088
• DOI: 10.1002/joc.7350

Southeastern South America is subject to considerable precipitation variability on seasonal to decadal timescales and has undergone very heavy land‐cover changes (LCCs) since the middle of the past century. The influence of local LCC and precipitation as drivers of regional evapotranspiration (ET) long‐term trends and variability remains largely unknown in the region. Here, ensembles of stand‐alone dynamic global vegetation models (DGVMs) with different atmospheric forcings are used to disentangle the influence of those two drivers on austral summer ET from 1950 to 2010. This paper examines the influence of both the El Niño‐Southern Oscillation (ENSO) and the dipole‐like first‐mode of southeastern South American precipitation variability (EOF1) on regional ET. We found that in the lower La Plata Basin, ET was driven by precipitation variability and showed a positive summer trend. Moreover, the region showed marked seasonal anomalies during El Niño and La Niña summers but mainly during EOF1 phases. On the contrary, in the upper La Plata Basin, LCCs forced the negative summer ET trend and particularly reduced the summer anomalies of the late 1990s, a period of ENSO and EOF1‐positive phases. In the South Atlantic Convergence Zone region, the high ET uncertainty across ensemble members impeded finding robust results, which highlights the importance of using multiple DGVMs and atmospheric forcings instead of relying on single model/forcing results. The South Atlantic Convergence Zone has considerable uncertainty in evapotranspiration (ET) interannual variability and no detectable summer trends despite major land‐cover change (LCC) since 1950. In the upper La Plata Basin, extreme LCC (27% of natural vegetation left by 2010) caused a negative summer ET trend. During summer, ET in the lower La Plata Basin shows a positive trend attributable to precipitation, and variability is governed by El Niño‐Southern Oscillation and the first mode of southeastern South American precipitation variability.