Análise de tendências e seus pontos de mudança na precipitação do estado do Rio Grande do Norte

Abstract

Over the past few years, increasingly stronger evidence of possible climate change has surfaced, and its present and future effects in climate dynamics have been a constant object of study. It is predicted that these changes will have a considerable impact in water resources engineering, especially regarding the distribution, frequency and intensity of rainfall events. This research, by consequence, aimed to investigate the existence of trends and change points in time series data ranging from 1963 to 2010, from 48 rain gauges in the Brazilian state of Rio Grande do Norte – which is located, in its majority, in an area of semiarid climate that often goes through severe droughts. Thirteen indexes related to total and extreme values of precipitation were calculated for each time series, and three different methods to detect these changes have been chosen: the Mann-Kendall test for trend detection (with a pre-whitening approach for autocorrelated time series), the Theil-Sen method for slope estimation and the Pettitt test for change-point detection. Results show that, even though the changes in annual total precipitation were not significant in their majority, various trends were identified for other indexes: drought periods have become longer, precipitation events seemed to occur in fewer days and, mainly in the eastern portion of the state, indexes associated with the frequency and intensity of extreme events presented positive trends in several stations. Furthermore, when analyzed in a seasonal scale, total precipitation seemed to decrease in numerous rain gauges over the years, both in rainy and dry seasons. The Pettitt test attested that most of the detected change points represented a positive variation, mostly for extreme event indexes and for the duration of drought periods, and mostly occurred between the years of 1990 and 1995. Even though some of the observed changes in this study can be partially explained by natural climatic phenomena that occur periodically within the region, their persistence and significance might represent important challenges for water resource management and risk prevention in the state of Rio Grande do Norte.