Long-Term Change and Regionalization of Reference Evapotranspiration in the Brazilian Northeast

Abstract

Evapotranspiration (ET) is the second most important variable in the hydrological cycle and influences several atmospheric processes. Therefore, the scientific interest in studying changes in that variable under the context of climate change and the usual occurrence of droughts in the Northeast of Brazil (NEB) is particularly valid. ET trends in the NEB were analysed from high resolution grid data (0.25°x0.25°) for the period between 1980 and 2016, comprising 2071 points in the NEB. A cluster analysis has shown that the region is climatically divisible into four homogenous groups. Group 1 represents the semiarid area in the central portion of the NEB. Group 2 is formed by the non-contiguous lands that surround the semiarid region. Group 3 is located in the north of Maranhão, whereas Group 4 is composed of patches spreading mostly over the eastern coast and the northwest of the NEB. By analysing the mean ET trend, it is possible to observe that groups 2, 3 and 4 show significant upward trends of 2.7 mm/year, 3.51 mm/year and 2.57 mm/year, respectively. According to a step-by-step analysis, the central (semiarid) area of the NEB presented a positive ET trend (~0.8 mm/year), whilst the northwestern coast and part of central Bahia showed negative trends (~ -1 mm/year). Such results may be linked to recent temperature and rainfall trends observed in the NEB, with important impacts for the desertification nuclei observed in many parts of the region, which represent a warning for environmental and water resources managers.

Keywords:
evapotranspiration; cluster analysis; trend analysis; Mann-Kendall test