Variabilidade dos fluxos de energia e evapotranspiração sob influência do enos no Bioma Pampa brasileira

Abstract

The Brazilian Pampa Biome is located in the extreme south of Brazil, in the humid subtropical climate region, with a uniform distribution of precipitation throughout the year, which favors the development of agricultural activities, mainly livestock due to the predominance of grass vegetation. Several studies have shown that precipitation in the Brazilian pampa biome is altered in the occurrence of the ENSO phases (El Niño/Southern Oscillation). ENSO is an atmospheric oceanic phenomenon that occurs in the Tropical Pacific, having two phases: the warm phase (El Niño) and the cold phase (La Niña), bringing climate change to different regions of the world. These changes can influence different climate system variables differently. In this work, we study the influence of the ENSO phenomenon on the surface energy balance components, on evapotranspiration (ET) and on atmospheric variables in the Brazilian Pampa Biome region. For that, data obtained from a flux tower were used, which has carried out measurements of the components of the energy balance and atmospheric variables in a livestock area under a native field of the Pampa biome, located in the municipality of Santa Maria - RS. The surface fluxes (radiation balance - Rn; energy to heat the atmosphere - H and energy for the physical state change of water - LE) were obtained every 30 min. through the Eddy Covariance method for 7 years (2015 to 2021). During this period, there was an El Niño (2015/2016) and two La Niñas (2017/2018 and 2020/2021). The anomalies of surface fluxes and environmental variables in relation to the average in the study period were used to assess the influence of ENSO in the region. The results showed that in both ENSO phases there are considerable changes in the environmental variables of precipitation, global radiation, soil water content, soil temperature, vapor pressure deficit and relative humidity. There were significant changes in surface fluxes, with H showing a predominantly negative anomaly in the El Niño period and positive in La Niña and LE showing predominantly negative anomalies in both ENSO periods. Unlike the real ET, the reference ET showed positive anomaly values in the La Niña period. All the variables studied in this work presented accentuated values (both negative and positive) of anomalies in the months corresponding to spring in the southern hemisphere, corroborating with more information about the behavior of these variables under the influence of ENSO in this important Brazilian biome.