Analysis of precipitation time series using the wavelet transform

Abstract

The water erosion in semiarid region of northeastern Brazil is mainly influenced by the intense rainfalls, which can occur during long periods of drought, when a large amount of sediment yield can be observed during such events. Thus, this paper aims to study the rainfall frequencies in such region through the wavelet transform. An application of wavelet analysis is done with long time series of the total monthly rainfall amount of several places from Paraíba state in northeastern Brazil. The main frequency components in the time series are studied by the global wavelet spectrum and the modulation in separated periodicity bands were done in order to extract additional information, e.g., the 8 and 16 months band was examined by an average of all scales, giving a measure of the average annual variance versus time, where the periods with low or high variance could be identified. In Taperoá II and Bodocongó raingages, important reductions were observed in the average variance for the following periods: 1998 to 2000 and 1993 to 1997, which can be considered as dry periods. Although, the precipitation in Taperoá II and Bodocongó raingages showed a similar global wavelet spectrum, their wavelet spectrum revealed particular features. This study can be considered an important tool for time series analysis, which can help the studies concerning soil erosion and land degradation, mainly when they are applied together with runoff-erosion simulations.