Climate classification for Northeast Brazil using reanalysis data and the Absolute Aridity Index

Abstract

The climate of the Northeast Region of Brazil (NEB) has been intensively studied and analyzed for climate classification. The aridity index of the United Nations Environment Programme (UNEP) (AIUNEP) has been used for this purpose, but without fully satisfactory results. The input variables needed for its calculation are precipitation and reference potential evapotranspiration (ET0). However, although rainfall stations recording routine measurements of precipitation are well distributed in the NEB, they do not provide the necessary variables for estimating ET0. Thus, interpolation is used to calculate ET0, but this can generate errors. Another objective climate classification approach is the Thornthwaite method, based on the determination of the moisture index (Im), whose calculation also requires weather station data. Thus, seeking to circumvent the problem of paucity of stations and improve the spatial distribution of information on meteorological variables in the NEB, the present work had as one of its objectives to validate reanalysis data from ERA5 of the European Center for Medium-range Weather Forecast (ECMWF) and the unified gauge-based analysis of global daily precipitation project of the Climate Prediction Center/National Oceanic and Atmospheric Administration (CPC/NOAA). After validation, climate classifications were developed for the NEB using the AIUNEP and Im. It was observed that the Thornthwaite climate classification overestimated the aridity in the NEB, while the IAUNEP tended to underestimate it. For this reason, a new climate classification index, called the absolute aridity index (Iab), was suggested, yielding satisfactory results.