Droughts Amplify Differences Between the Energy Balance Components of Amazon Forests and Croplands

Charles Caioni,Michael T. Coe,Marcia N. Macedo,Divino Vicente Silvério,Paulo M. Brando

doi:10.3390/rs12030525

Abstract

Droughts can exert a strong influence on the regional energy balance of the Amazon and Cerrado, as can the replacement of native vegetation by croplands. What remains unclear is how these two forcing factors interact and whether land cover changes fundamentally alter the sensitivity of the energy balance components to drought events. To fill this gap, we used remote sensing data to evaluate the impacts of drought on evapotranspiration (ET), land surface temperature (LST), and albedo on cultivated areas, savannas, and forests. Our results (for seasonal drought) indicate that increases in monthly dryness across Mato Grosso state (southern Amazonia and northern Cerrado) drive greater increases in LST and albedo in croplands than in forests. Furthermore, during the 2007 and 2010 droughts, croplands became hotter (0.1–0.8 °C) than savannas (0.3–0.6 °C) and forests (0.2–0.3 °C). However, forest ET was consistently higher than ET in all other land uses. This finding likely indicates that forests can access deeper soil water during droughts. Overall, our findings suggest that forest remnants can play a fundamental role in the mitigation of the negative impacts of extreme drought events, contributing to a higher ET and lower LST.

Highlights

20% of Amazon vegetation and 50% of Cerrado have already been converted to other uses [1], largely pastures and croplands [2,3,4,5]
When we analyzed mean changes in energy balance components across the entire state of Mato Grosso, we found an overall increase in surface temperature and albedo during the droughts of 2007 and 2010
We found that the effects of drought on the land surface temperature (LST) and albedo are greater in areas of cropland and savanna in comparison with forested environments in the Brazilian state of Mato Grosso

Summary

Introduction

20% of Amazon vegetation and 50% of Cerrado have already been converted to other uses [1], largely pastures and croplands [2,3,4,5]. Mato Grosso accounted for 24% of deforestation in the Cerrado biome from 2014 to 2017 [7] Such changes in land use are expected to drive important regional climatic changes [8,9] because deforested areas covered by crops and pastures tend to be warmer and evapotranspire less [10,11,12] than areas covered by native forests and savannas. Such deforestation-induced climate changes have the potential to amplify drought effects on vegetation [13]

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Conclusion