Seasonal trend of climate variables in an area of the Caatinga phytogeographic domain

Abstract

Wide variability in the rainfall regime and drought is characteristic of semi-arid regions. A better understanding of this variability can aid decision-making in the short, medium and long term. The aim of this study was to identify long-term patterns and trends in rainfall and temperature through the use of temporal patterns, in addition to assessing the duration of wet and dry periods. Daily historical series of rainfall and temperature for the district of Iguatu, Ceará were used. For rainfall, the annual and monthly climate normal (1974-2018) was calculated, in addition to the number of consecutive dry days (CDD) during the rainy season. The annual mean value for the maximum, mean, and minimum temperatures (1996-2017) was also calculated. Wide interannual variability in the rainfall was found, with very wet years (1985; 2009 and 2011) and very dry years (1979; 1983 and 1993) interspersed with periods of around average rainfall. When analysing the total occurrence of dry spells by class, it was found that events of from 5 to 10 days were the most frequent, and tended to reduce in number over the period under investigation. There was also an increase in the number of longer events, those over 16 days. Maximum annual temperatures show an increasing trend over the years, with minimum temperatures showing the smallest increases. It was concluded that extreme rainfall events are common, and alternate between rainy years and years of drought. The increase in maximum temperature and the reduction in rainfall express the extreme climate variability that may be a consequence of climate change.