Dinâmica da seca no perímetro urbano de Altamira/PA: evolução das últimas quatro décadas

Abstract

Drought has been becoming an increasingly frequent and major natural disaster in the Amazon region, causing numerous environmental and socioeconomic impacts. Studies indicate that these changes are related to changes in land use and cover that cause soil degradation, generally associated with practices using fire to prepare land in family farming, which often become forest fires. Deforestation also makes the drought worse, which increases the incidence and favors conditions for forest fires, which in turn cause further changes in land cover. This study aims to evaluate drought patterns in the urban perimeter of Altamira-PA, from 1983 to 2022, based on changes in land use and cover and on the behavior of climatological variables (precipitation and air temperature) and elevations of the Xingu river. The series of precipitation, air temperature and elevations of the Xingu river, with a time frame of 40 years (1983 - 2022), were obtained respectively from ERA5 reanalysis data and the National Water Agency's fluviometric station. The land use and cover data were collected from the MapBiomas project for the years 1986, 1993, 2003, 2013 and 2022. The results indicate significant changes in land use and cover with a reduction of 27.2% (17.3km2) of the forest class, and an increase of 238.5% (18.6km2) of non-vegetated area, which occurred continuously and gradually. The drought events increased in all categories by a total of 44%, divided as follows: weak drought (28%), moderate (138%), severe (36%) and extreme drought (33%). The annual variability of precipitation confirms the existence of a less rainy period, between June and November, with precipitation between 43mm and 62mm. And a rainy period, between December and May with rainfall between 275mm and 328mm. The variability of elevations of the Xingu river follows these periods, varying between minimums of 290cm to 330cm and maximums between 611cm and 702cm. The highest air temperatures, between 31.6ºC and 32.3ºC, occur in the less rainy season, and the lowest temperatures, around 22.8ºC, occur in the rainy season. The average annual precipitation in the rainy season shows an increase above the average of 256mm over the years, while in the less rainy period, the behavior is a reduction below the average of 71.5mm over the four decades. In the same period, the air temperature showed an increase in minimum temperatures by 0.3ºC, average temperatures by 0.6ºC and maximum temperatures by 0.5ºC. This study concludes that the change in land use and cover, with emphasis on deforestation and forest fires, associated with reduced precipitation in the less rainy period and increased air temperature, demonstrate an influence on the occurrence of drought and the increase in the number of events, especially of moderate and severe magnitudes, during the study period.