Análise e influência da hidroclimatologia e do balanço hídrico climatológico na cobertura vegetal do Estado de Alagoas, Nordeste do Brasil

Abstract

The relationship between water supply (precipitation) and demand (evapotranspiration) is a central component necessary to understand environmental impacts at a regional scale. In the semi-arid region of Alagoas, potential evapotranspiration (PET) exceeds precipitation for most of the year, on the other hand, the coast has a higher concentration of rainfall. Therefore, the main objective of this study was to account for and analyze the influence of the Climatological Water Balance (CWB) on the vegetation cover of the state of Alagoas. To this end, a monthly precipitation and PET database was used, covering the period 1961 to 2020 (60 years) with a spatial resolution of 0.1° x 0.1°, along with data from the Enhanced Vegetation Index (EVI). Using the data, descriptive and inferential statistics were applied to analyze precipitation and PET data at monthly, annual, decadal, and climatological normal scales (1961-1990 and 1991- 2020). The Thornthwaite and Mather (1955) method was adopted to calculate the CWB, considering a soil available water capacity (SWC) of 100 mm. The Mann-Kendall, Sen, and Pettitt tests were applied to verify, respectively, the presence of a trend, the magnitude, and the onset of the trend in the precipitation and PET time series. Pearson's correlation was used to estimate the linear correlation between the CWB variables and the EVI, in the dry and rainy seasons, and annually. Precipitation was found to be highly irregular, both spatially and temporally, with a short rainy season (3 to 5 months) and higher precipitation amounts along the coastal strip. On the other hand, the PET showed less variability, and the largest quantities were concentrated in the Sertão region of Alagoas. It was also observed that the most recent decades (1990, 2000, and 2010) were the least rainy, consequently the 1961-2020 Climatological Normal was the driest. For the CWB, it was identified that, on average, there is a water surplus only in the eastern portion of the state (May to August), with water storage decreasing as one moves westward. According to the Thornthwaite and Mather methodology, the state has four climate types, with humid and subhumid climates predominating in the east, and dry subhumid and semiarid climates in the west. 47% of Alagoas' municipalities had different climates from 1991 to 2020 compared to 1961 to 1990, with a predominant shift toward drier climates. Precipitation trends decreased in the extreme west of the state during the rainy season, transition seasons, and annually. There are also increasing trends in PET in the region. The correlations between the EVI and the CWB variables were more intense and significant in regions with dry subhumid and semiarid climates, with a water deficit highlighted. The conclusion is that the CWB for the state of Alagoas exhibits high variability in time and space, with significant water limitations in the western portion. It should be noted that these limitations may be intensifying with the decrease in precipitation in recent decades and the climatological normal throughout the state. Therefore, these results are useful for water management in various sectors of the environment and society.