Influência do desmatamento na evapotranspiração real do Estado de Alagoas, Nordeste do Brasil

Abstract

Actual evapotranspiration (ETr) is the loss of water to the atmosphere resulting from evaporation plus plant transpiration, and depends on a combination of factors, including the energy demand of the atmosphere, the type/use of land cover and surface water restriction. Changes in land use and cover, especially deforestation, can significantly affect ETr, impacting the availability of water resources and regional climate dynamics. The application of vegetation indices, such as the EVI (Enhanced Vegetation Index), has contributed to understanding and monitoring the dynamics of water on the earth's surface. In the state of Alagoas, which has two climatic types (tropical and semi-arid), the distribution of moisture in the soil and vegetation varies, influenced by these conditions and with great irregularity in time and space. The general objective of this work is to analyze the impacts of changes in land cover on ETr processes in the state of Alagoas. For this work, we used data from the MOD16 product, which provides ETr estimates globally, data from the MOD13 product, which provides information on EVI, and precipitation data from Xavier et al. (2022), both for the period from 2001 to 2020. Land cover will be analyzed using images from 2001, 2010 and 2020, obtained from the MapBiomas platform. Descriptive statistical analyses were carried out to understand the spatial and annual variability of ETr in Alagoas. For comparative purposes, a rainy quarter (May, June and July), a dry quarter (October, November and December) and the annual total were considered. The areas with similar ETr characteristics were regionalized using cluster analysis, while the Silhouette Index was applied to validate the groups separated into sub-regions. The main results include an average ETr of 98.9 mm/month in the rainy quarter (CV = 20.8%) and 56.9 mm/month in the dry quarter (CV = 40.3%), with an annual average of 827.9 mm per year. Regionalization identified four homogeneous ETr sub-regions (S1 to S4). Significant ETr trends (p < 0.05) were concentrated in the Atlantic Forest (90.9% in the rainy season; 93.1% in the dry season; 82.6% annually), in contrast to 9.1%, 6.9% and 17.4% in the Caatinga, respectively. Positive correlations, with statistical significance of 5%, between EVI and ETr reinforced that the reduction in vegetation decreases ETr. The historical series from 2001 to 2020 showed a general downward trend in ETr, linked to the replacement of native vegetation by anthropogenic areas, which implies a reduction in the availability of moisture in the soil. These results fill gaps in knowledge about the behavior of ETr in Alagoas and how it is an important hydrological and soil cover indicator, so there is a need for public policies aimed at preserving native vegetation and sustainable soil management.