Variabilidade espaço-temporal da evapotranspiração real em Alagoas usando sensoriamento remoto

Abstract

Evapotranspiration is the loss of water to the atmosphere resulting from the sum of water evaporation plus plant transpiration (vegetated surface), and can be an indicator of water deficiency in the soil, especially in tropical regions. The state of Alagoas, even being the third smallest in Brazil, has two climatic types (tropical and semi-arid) which reverberates in an unequal distribution of soil moisture in different types of vegetation, soils, among others. The main objective of this research is to characterize the spatial and temporal variability of the Real Evapotranspiration (ETr) for the state of Alagoas. For this, monthly data were used from 2001 to 2020 through the MOD16 Product that provides ETr data across the globe. The descriptive statistics (mean, minimum and maximum values, coefficient of variation) were performed to characterize the spatial and annual variability of ETr in the state of Alagoas in two distinct situations: one month of the rainy period (July), another of the dry period (December) and annually. Then the ETr data were compared with the type of land cover, using data from MapBiomas Brasil. The ETr variability (in the wet and dry periods) was also compared with the variability of precipitation (2001 to 2020) for two sites with data availability: one inserted in the semi-arid region (Água Branca) and the other in the Zona da Mata (Maceió), both in Alagoas, with data provided by the National Institute of Meteorology (INMET). In the rainy period, it was observed that, on average, the ETr is 99.3 mm/month/year registering a minimum and maximum value of 35.0 and 181.2 mm, respectively. In the dry period the lowest ETr values are obtained, averaging 50.3 mm/month/year, with a minimum of 13.5 mm/month/year and a maximum of 227.4 mm/month/year. The annual accumulated ETr, presents an average of 827.9 mm/year with minimum and maximum values, respectively, from 182.6 to 2225.9 mm/year. In the rainy season month, Maceió recorded the highest precipitation in the year 2017 (645.8 mm/month), which contributed to the high value of ETr (115.90 mm/month). In Água Branca, for the rainy season, the year 2006 stood out with one of the highest monthly precipitation amounts (308.6 mm/month), which culminated in the occurrence of ETr above the average (135.1 mm/month). For the dry period, Maceió in the first two years of the series (2001 and 2002) showed precipitation of 115.9 mm/month and 3 mm/month, respectively, and it is observed that the ETr value also decreased, with respective values of 60.7 mm/month and 32.6 mm/month. It was also observed that areas modified by anthropic actions have expanded in the state of Alagoas, and, on the other hand, there was a reduction, in these areas, of water availability for evapotranspiration. The biggest change is presented in the caatinga biome with an increase of anthropized areas, mainly by the advance of the dairy basin. It is concluded that ETr, besides being an important component of the hydrological cycle, can also be an important indicator of water availability and vegetation cover. These investigations will be deepened in future studies.