Variabilidade espacial e temporal da precipitação na bacia hidrográfica do Rio Parnaíba, Nordeste do Brasil

Abstract

The National Water Resources Policy constitutes a strategic planning to promote the participative management of water resources. In this context, the Parnaíba River Watershed (PRW) is one of the most important watersheds in the Northeast region of Brazil, encompassing parts of Ceará, Piauí and Maranhão States (331,441 Km²), where nearly 4 million inhabitants dwell. Thus, the aim of this study was to analyze the spatial and temporal variability of precipitation in the PRW. To achieve this objective, observed data between 1980 and 2013 and arranged in a high resolution grid (0.25º x 0.25º) by Xavier, King and Scanlon (2015) were used. Cluster analysis was used in order to divide the PRW into homogeneous rainfall subregions. Results showed that, regarding year-to-year variability, the years of 1985 (1800 mm) and 1989 (1500 mm) presented the highest annual totals, while 1983 (761 mm) and 2012 (670 mm) presented the lowest values. These peaks might be associated with sea surface temperature anomalies in the Pacific Ocean, with its positive phase (La Niña) occurring during the wetter years and the negative phase (El Niño) taking place during 1983, which was one of the driest years. The monthly distribution of rainfall showed two seasons: one between May and October (<100 mm) and the other between November and April, with rainfall between 50 and 350 mm, with the Intertropical Convergence Zone causing most of the rainfall. Four homogeneous groups were identified: one located at the lower Parnaíba (1000 - 1600 mm); one comprising the east part of the PRW (600 - 1000 mm); one covering the south-central PRW (800 - 1400 mm); and the last group located at the higher Parnaíba (1200 – 1600 mm). The characterization performed in this study can be used as a water resources management tool by decision makers in the studied region