Vegetation degradation in ENSO events: Drought assessment, soil use and vegetation evapotranspiration in the Western Brazilian Amazon

Abstract

In recent years, the degradation of the Amazon forest has been the target of studies at the global level to identify elements and factors influencing this process. Thus, this study had as objective to study the vegetation degradation during the years of El Niño Southern Oscillation (ENSO) phenomenon in the State of Amazonas. We used remote sensing data, forest typologies, and weather elements from 14 conventional stations located in Amazonas. Evapotranspiration images obtained from the MODIS Global Evapotranspiration Project (MOD16A2), and data from fire sources from the Terra and Aqua collection (MOD146) platforms were used. The 6 different forms of forest typologies found in the region were also used, in addition to the climatic elements maximum, minimum temperature, relative humidity, sunshine and wind speed of 14 conventional stations in the state of Amazonas. The weather station data were used to estimate the reference evapotranspiration, using the empirical methods Val-1, Val-2, Val-3, Val-4, Irmak-1, Irmak-2 and Alex. The results show differences in the correlations between the evapotranspiration methods used. The highest evapotranspiration was found in the Open Ombrophilous Forest. Fire foci were concentrated in Dense Ombrophilous Forest areas. The Standardised Precipitation-Evapotranspiration Index (SPEI) showed to be an efficient index to characterize the drought in El Niño events, besides showing the agricultural expansion in the region. The largest trends of the weather elements and the SPEI were during the El Niño phenomenon. A better understanding of the ENSO effects on vegetation could prevent uncontrolled forest loss. Governance interventions involving national and financial actors, as well as local populations, also play a role in this.