Aridity is a climate characteristic that results from the water deficit generated by insufficient average precipitation and its relationship with potential evapotranspiration in a given region. The aridity of an area is characterized by the aridity index, which is the ratio between precipitation and the evaporation demand of the atmosphere. Thus, if the index is less than 1, it means that atmospheric demand is greater than precipitation, which occurs in drier climates such as the Caatinga biome (shrubland in semiarid Brazil). When the index is greater than 1, precipitation is sufficient to meet the entire evaporation demand of the atmosphere, which can be seen in the Amazon biome.
Using the aridity index, it is possible to identify, locate, or delimit regions with a variable deficit of available water. This condition can severely affect the effective use of land for activities such as agriculture or livestock, which favors the occurrence of fires, and which in the long term can lead to desertification when associated with unsustainable land use.
Using a recently published climatological database, researchers from INPE and Cemaden analyzed the variation in precipitation and evapotranspiration between 1960 and 2020. In this type of study, it is essential to consider average data over 30 years, as rainfall variations between one year and the next can mask long-term trends. Thus, the periods 1960-1990, 1970-2000, 1980-2010, and 1990-2020 were considered in the analyses.
The study found a tendency for aridity to increase throughout the country, except for the southern region and the coast of Rio de Janeiro and São Paulo. These variations are mainly due to increased evapotranspiration associated with increased temperature, which has been observed in a large part of the country. In the case of the southern region, the decrease is related to the increase in rainfall.
The study found that the country's semi-arid areas have grown at an average rate of more than 75 thousand km2 for each decade considered. The areas classified as semi-arid are concentrated in the Northeast region (except Maranhão) and the north of Minas Gerais. Regarding dry subhumid areas, in addition to the Northeast and North of Minas Gerais, occurrences were identified in the North of Rio de Janeiro and Mato Grosso do Sul. Finally, in the last period considered, 1990-2020, an area defined as arid in the north of the State of Bahia appeared, which had never been observed in the country in previous decades.
The diagnosis produced by INPE and CEMADEN will support the Brazilian Plan to Combat Desertification preparation.
More information at: https://www.gov.br/cemaden/pt-br/assuntos/noticias-cemaden/estudo-do-ce…
