Patterns and Controls of the Latent and Sensible Heat Fluxes in the Brazilian Pampa Biome

Gisele Cristina Dotto Rubert,Vanessa De Arruda Souza,Tiago Bremm,Luis Gustavo Gonçalves De Gonçalves,Débora Regina Roberti,Anderson Ruhoff,Gustavo Pujol Veeck,Tamíres Zimmer,Alecsander Mergen

doi:10.3390/atmos13010023

Gisele Cristina Dotto Rubert, Vanessa De Arruda Souza + Show 7 more

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https://doi.org/10.3390/atmos13010023

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Abstract

Energy and water exchange between the surface and the atmosphere are important drivers to Earth’s climate from local to global scale. In this study, the energy dynamic and the biophysical mechanisms that control the energy partitioning over a natural grassland pasture over the Brazilian Pampa biome are investigated using two micrometeorological sites located 300 km apart, in Southern Brazil. The latent heat flux, LE, was the main component of the energy balance in both autumn-winter (AW) and spring-summer (SS) periods. Annually, approximately 60% of the available energy is used for 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 heat flux, H. Hysteresis curves in the daily cycle were observed 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, this study can be used as a base for research on land-use changes in this unique ecosystem of the Pampa biome.

Highlights

IntroductionUnderstanding the main mechanisms responsible for the partitioning of net radiation (Rn) energy used to heat the atmosphere (sensitive heat flux, H), the subsoil (soil heat flux, G), and changing the water’s physical state (latent heat flux, LE, or evapotranspiration, ET) is essential for climate studies and weather forecasts, as necessary on providing useful information to improve water resources management
Understanding the main mechanisms responsible for the partitioning of net radiation (Rn) energy used to heat the atmosphere, the subsoil, and changing the water’s physical state is essential for climate studies and weather forecasts, as necessary on providing useful information to improve water resources management
This study aims to advance in the understanding of the annual and seasonal variability and the biophysical mechanisms that control the energy balance components in natural pasture areas over the Pampa biome in southern Brazil

Summary

Introduction

Understanding the main mechanisms responsible for the partitioning of net radiation (Rn) energy used to heat the atmosphere (sensitive heat flux, H), the subsoil (soil heat flux, G), and changing the water’s physical state (latent heat flux, LE, or evapotranspiration, ET) is essential for climate studies and weather forecasts, as necessary on providing useful information to improve water resources management. The ET process is linked directly to energy partitioning, stomatal conductance, carbon exchange, and water availability through the water-use efficiency by the plants acting as a key regulator of the ecosystems processes [1–3]. Grasslands are one of the most widespread vegetation types, accounting for approximately 32% of the planet’s natural vegetation [4], making them important when studying the global vegetation dynamics and responses of ecosystem physiology to environmental change. Studies have shown that pasture ecosystem degradation alters its structure and ecosystem productivity and affects surface–atmosphere interactions, changing heat and water transport [10–13]

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