ANALYSIS OF PRECIPITATION NON-STATIONARITY IN THE STATE OF RIO GRANDE DO NORTE, BRAZIL
Non-stationarity. Precipitation. Trends. Water resources. Climate change.
Over the last years, increasingly stronger evidence of global warming has surfaced, and its present and future effects in the 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. In general, however, it is assumed that precipitation varies randomly over time inside a certain expected variability, which would mean its behavior is stationary, and this principle guides urban drainage projects, reservoir operation planning, drinking water management, etc. Nevertheless, by observing precipitation time series, trends and shifts can be sometimes identified, which would classify their behavior as non-stationary, a trait that might become more usual in the context of climate change. This research project, by consequence, aims to investigate the existence of non-stationarity in time series data of 50 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. In this study, the selected data ranges from 1963 to 2010, and, based on a series of 13 indices related to total and extreme values of precipitation, four different methods to detect these changes have been chosen: the Mann-Kendall and Spearman tests for trend detection, the Theil-Sen slope estimator and the Pettitt test for change-point detection. Preliminary results have been presented for the city of Natal, the state’s capital, in which significant signs of a trend towards less consecutive wet days have been identified, while at the same time extreme rainfall events seem to have become more frequent and intense.