As delimitações das áreas semiáridas do Nordeste do Brasil e norte de Minas Gerais podem apresentar grandes diferenças conforme os métodos de classificação climática e de estimativa da evapotranspiração potencial (ET0) utilizados. Para demostra esta afirmação de forma quantitativa, nesta pesquisa, delimitou-se as áreas semiáridas usando dois métodos de classificação climática (1) índice efetivo de umidade de Thornthwaite (Im) e (2) índice de aridez do Programa das Nações Unidas para o Meio Ambiente (IaUNEP), enquanto, para a estimativa da ET0 usou-se os métodos de (1) Thornthwaite e (2) Penman-Monteith-FAO (PMF), totalizando quatro diferentes configurações de delimitações de áreas semiáridas. Com a utilização de Im observou-se um aumento do grau de aridez e de áreas semiáridas quando comparado com os resultados obtidos com o uso de IaUNEP. Do mesmo modo, ao usar a estimativa de ET0 pelo método PMF verifica-se um aumento da aridez e das terras semiáridas em comparação com a ET0 calculada por Thornthwaite. Como o método PMF é geralmente reconhecido como um método padrão para estimativa da ET0. Portanto, é possível certificar que o grau de aridez e de terras semiáridas no Nordeste do Brasil são mais elevados do que aqueles mostrados nos estudos com a estimativa de ET0 por Thornthwaite. Classification of semi-árid and sub-humid sreas using different climate indexes A B S T R A C TThe delimitations of semi-arid areas in the Northeast of Brazil and northern Minas Gerais can present great differences according to the methods of climatic classification and estimation of potential evapotranspiration (ET0) used. To demonstrate this statement in a quantitative way, in this research, we used two different methods of climate classification: (1) the moisture index of Thornthwaite (Im) and (2) aridity index of the United Nations Environment Program (IaUNEP), as well as, two methods to estimate ET0: of (1) Thornthwaite and (2) Penman-Monteith-FAO (PMF), totaling four different configurations of delimitations of semi-arid areas. As the use of Im an increase in the degree of aridity and semi-arid areas was observed when compared with the results obtained as the use of IaUNEP. Similarly, when using the ET0 estimate using the PMF method, there is an increase in aridity and semi-arid land compared to the ET0 calculated by Thornthwaite. As the PMF method is generally recognized as a standard method for estimating ET0. Therefore, it is possible to affirm that the degree of aridity and semi-arid lands in Northeast Brazil are higher than those shown in studies with the estimate of ET0 by Thornthwaite. Keywords: Semiarid, climatic classification, potential evapotranspiration

Agricultural Zoning of Climate Risk (AZCR) is a fundamental tool for agricultural activities because it identifies regions and times of lower climate risk for planting and sowing crops, aiming to minimize the agricultural losses arising from climate hazards. In Brazil, AZCR has been used since 1996 as an official agricultural policy instrument. However, optimal AZCR representative of large areas require a network of meteorological stations with excellent spatial distribution, routine and accurate observations, and reliable data. Precipitation gauges that perform reliable measurements of precipitation have a good distribution in the Northeast region of Brazil. However, weather stations in this region are scarce. When weather stations are absent at a given location, input variables for AZCR are interpolated, which can lead to errors. Thus, seeking to solve the problem of the shortage of weather stations and improve the spatial distribution of information on meteorological variables, this study aimed to validate data from the ERA5-Land reanalysis of the European Center for Medium-Range Weather Forecasts and the CPC Precipitation Project. Once the data were validated, an AZCR was performed for the maize crop in the entire state of Bahia, in a 0.5° x 0.5° grid. It was observed that, with the exception of the far north mesoregion and a small area in the valley of Paraguaçu, the state of Bahia presented large areas suitable for planting of maize crops at different times of the year, with emphasis on areas in the southeast of the state that are suitable for planting all year round.

Influência de práticas conservacionistas na recuperação de áreas degradadas no semiáridoInfluence of conservationist practices in the recovery of degraded areas in the semi-arid region

This study aimed to determine crop evapotranspiration through the soil water balance, the crop coefficient and water use efficiency of the onion (Allium cepa L.) in a system with four irrigation regimes, cultivated in the semiarid region of northeastern Brazil. Two field experiments were carried out during the rainy and dry periods of the region in 2018, using the treatments of 100% (T1), 75% (T2), 50% (T3) and 25% (T4) of the reference evapotranspiration for daily water replacement and five replicates for each treatment. It was verified that crop evapotranspiration varies according to the water availability in the soil; however, the highest water use efficiency occurred for the T3 treatment. The T1 treatment obtained the highest estimated yield, 43.86 tons ha-1, while T4 obtained 13.47 tons ha-1, the lowest estimated yield among the treatments, and this difference was statistically significant (p ≤ 0.05) by F test. The crop coefficients obtained were 0.68, 0.89, 0.99 and 0.73 for the initial, vegetative, bulbing and maturation stages, respectively.

The Climate of the Northeast Region of Brazil (NEB) has been intensively studied and analyzed. Studies have used objective climate classification methods such as the aridity index of the United Nations Environment Programme (UNEP) (AIUNEP), however, without fully satisfactory results. The input variables needed for calculation of the AIUNEP are precipitation and reference potential evapotranspiration (ET0). However, although rainfall stations that record routine measurements of precipitation data are well distributed in the NEB, weather stations that provide the set of variables necessary for the estimation of ET0 are scarce. When weather stations are absent in a location, ET0 is interpolated, but this can lead to errors. Another objective climate classification approach is the Thornthwaite method, which is based on the determination of the moisture index (Im), whose calculation also requires weather stations data. Therefore, seeking improve the spatial distribution of information on meteorological variables in the NEB, the present work had as one of the 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, climatic classifications were developed for the NEB using the AIUNEP and Im indices. It was observed that Thornthwaite climate classification tended to overestimate the aridity of the NEB, while the classification using AIUNEP tended to underestimate it. For these reasons, a new climate classification index, called absolute aridity index (Iab), yielding satisfactory results.