Abstract
Abstract Uncertainties in the timing and quality of rainy season are a threat for food and water security, and also in terms of fire vulnerability. Then, understanding features associated to rainfall allows a climate characterization useful for climate and fire risk management. We used rainfall data series (1983-2018) from 15 meteorological stations to characterize the greatest conservation area of Brazilian-unique seasonally dry tropical forest Caatinga (northeastern Brazil). Accumulated anomalies in daily series were used to determine onset and end of rainy seasons. We also determined seasonal and annual rainfall (quality) and rain rate, and performed a dry season sub-classification. Results showed greater variability for end dates as compared to onset dates for rainy season. Droughts in the region are becoming more severe. We found a significant decreasing tendency of 7 mm/year on annual rainfall, of 0.3 mm/day per decade on rain rate, and an increase of 12 days per decade on consecutive dry days. Dry season length presented a 14-year periodicity and is related with previous but uncorrelated from posterior rainy season length. The complexity of the rainfall patterns is evidenced by the weak correlation we found between the amount of rainfall and the rainy season length.
Highlights
Semiarid environments are mainly characterized by alternating rainy and dry seasons, rainfall concentration, periods of pronounced water shortage, and the occurrence of fires (Allen et al, 2017; Archibald et al, 2013; Prăvălie, 2016)
We focused on a region of semiarid northeastern Brazil (NEB) that includes two fully protected areas: Serra das Confusões and Serra da Capivara National Parks, that together constitute the greatest conservation area of the Brazilian-unique biome Caatinga and its ecotone with Cerrado
The negative tendency observed in annual rainfall could worsen in the future, since climate change scenarios indicate that the semiarid part of NEB will present rainfall deficit and increased aridity (Marengo and Bernasconi, 2015; Marengo et al, 2017; Vieira et al, 2015)
Summary
Semiarid environments are mainly characterized by alternating rainy and dry seasons (seasonality), rainfall concentration, periods of pronounced water shortage, and the occurrence of fires (Allen et al, 2017; Archibald et al, 2013; Prăvălie, 2016). Three of the most important quantities determining rainy season are onset, end, and rain rate (Liebmann et al, 2007). These quantities are important from meteorological and societal perspectives. Onset and end of rainy season represent sudden changes in a tropical atmospheric heat source, and its rate determines the magnitude of that heat source (Correia Filho et al, 2019; Horel et al, 1989; Liebmann et al, 2007). Length and severity of dry season affect forest biomass growth, the risk of fires, forest recuperation after disturbances (including fire), atmospheric carbon sequestration, and the sustainability of agricultural settlements (Sombroek, 2001)
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