Patterns and controls of the latent and sensible heat fluxes in the brazilian Pampa biome

Abstract

Energy and water exchange between the surface and the atmosphere are important drivers to Earth’s climate fromlocal to global scale. In thisstudy, the energy dynamic and the biophysical mechanisms thatcontrol the energy partitioning overa natural grassland pasture overthe Brazilian Pampa biome are investigated using two micrometeorological sites located 300 km apart, in Southern Brazil. The latent heatflux, LE, was the maincomponent of the energy balance in bothautumn-winter (AW)and spring-summer (SS)periods. Annually, approximately 60% of the available energy is usedfor evapotranspiration (ET). However, the Bowen ratio presents seasonal variability greater in AW than SS. Global radiation, Rg, is the atmospheric variable controlling LE and sensible heatflux, H. Hysteresis curves in the daily cycle wereobserved for ET and surface conductance, Cs, regarding the environmental variables, net radiation, vapor pressure deficit, and air temperature. Among the variables analyzed in the Pampa biome, surface conductance and evapotranspiration respond more strongly to the vapor pressure deficit. The hysteresis cycles formed by ET and conductance show a substantial biophysical control in the ET process. The results obtained here allowed a comprehension of the biophysical mechanisms involved in the energy partition process in natural grassland. Therefore, thisstudy can be usedas abasefor research on land-use changes in this unique ecosystem of the Pampa biome.