Resumo -Nas regiões de clima semiárido os recursos hídricos são limitados e seriamente ameaçados pela excessiva exploração. Objetivou-se com este estudo avaliar o desempenho do método Penman-Monteith FAO 56 (PM-FAO 56) para estimar a evapotranspiração de referência (ET o ) com dados mínimos (temperatura máxima e mínima do ar), no sertão do estado do Ceará. O trabalho foi desenvolvido a partir de dados de temperatura máxima e mínima do ar, umidade relativa do ar, velocidade do vento e insolação das estações convencionais da região do sertão cearense, obtidos com o Instituto Nacional de Meteorologia (INMET). Para comparar os valores de ET o estimados por PM-FAO 56 com dados completos e mínimos foram considerados a razão entre as médias (ξ), o erro padrão de estimativa (EPE), coeficiente de correlação (r), índice de exatidão ou concordância (d) e índice de confiança ou desempenho (c). Foram confeccionados mapas de ET o por PM-FAO 56 com dados mínimos para a mesorregião do sertão do Ceará, por meio do interpolador linear IDW (Ponderação do Inverso da Distância). O procedimento de estimativas de ET o por PM-FAO 56 com dados de temperatura máxima e mínima do ar funcionou satisfatoriamente e por meio da espacialização e geração de mapas temáticos, foi possível visualizar a ET o nas mais remotas áreas da região de estudo.
Palavras-chave -Clima semiárido. Disponibilidade de dados climáticos. Recursos hídricos.Abstract -In areas of semiarid climate, water resources are limited and seriously threatened by excessive exploitation. This study's objective is to evaluate the performance of the method FAO 56 Penman-Monteith (PM-FAO 56) to estimate the reference evapotranspiration (ET o ) with minimum data (maximum and minimum air temperature) in the backcountry of the state of Ceará. The work was developed based on maximum and minimum air temperatures, relative air humidity, wind speed, and insolation of the conventional stations of the backcountry of Ceará, obtained from the National Institute of Meteorology (INMET). To compare the values of ET o estimated by FAO PM-56 with complete data where the minimum was considered the ratio between the mean (ξ), the standard error of estimation (SEE), correlation coefficient (r), accuracy or concordance index (d) and performance or confidence index (c). Maps of ET o by PM-FAO 56 were made with minimum data for the mesoregion of the backcountry of Ceara, by means of the inverse distance weighted (IDW). The following of estimates of ET o by PM-FAO 56 with maximum and minimum air temperatures worked satisfactorily and by means of spatialisation and generation of thematic maps, it was possible to visualize the ET o in the most remote areas of the region of the study.
Probabilistic studies of climatic variables are of utmost importance for the planning of agricultural activities. In this context, we aimed to adjust the function Normal distribution to the values of precipitation and monthly potential evapotranspiration in order to determine the components of the water balance (deficits and excesses) with different levels of probabilities in Barreiras, Bahia. We used daily data of maximum and minimum air temperature and precipitation, period of 1961 to 2008. The potential evapotranspiration was estimated by the method of THORNTHWAITE (1948). In order to check the adherence of the estimated probabilities to the observed frequencies, we applied the adherence tests Chi-square (χ 2) and Kolmogorov-Smirnov (KS), at 5% of significance. We obtained the probable values of precipitation and monthly potential evapotranspiration for the following probabilistic levels:
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