Search

The aim of this study was to analyze hygrothermal data at two locations in the semiarid region of the Brazilian state of Rio Grande do Norte--RN, comparing one mountainous area (06°25'45" S and 37°00'18" W) with one area of depression (06°25'43" S and 37°04'58" W) in order to discover a vertical temperature gradient while also identifying the climatic differences that altitude brings about in a semiarid region. To do this, two automatic thermo-hygrometers were used, which recorded temperature and relative humidity data 24 h.d-1 during the dry season. Statistical techniques for measuring the central tendency and dispersion were used and the Pearson correlation coefficient (r) was used to analyze the temporal and spatial correlation between temperature, humidity, and altitude. The temperature in the mountains was milder and the relative humidity was higher than in areas of depression and the vertical temperature gradient was found to be 0.95°C/100 m. These results indicate that the mountains, or high-altitude wetlands, may truly be considered "oases" of cool, humid air compared to the prevailing hot, dry climate in the surrounding depression, making their conservation and preservation of the utmost importance from the perspective of the environment and from that of the development of different human activities. [ABSTRACT FROM AUTHOR]

Northeast Brazil's semiarid region is characterized by water deficit. However, little is known about the trends in joint water loss by evaporation and transpiration (evapotranspiration) in the region. Thus, this study aimed to analyze indications on the linear trend of reference evapotranspiration (ET0) in the monthly, annual, and interdecadal scales in irrigated agricultural areas in the microregions of Juazeiro, Bahia State (9° 24' S; 40° 26' W and 375.5 m), and Petrolina, Pernambuco State (09° 09' S, 40° 22' W, and 376 m). For this purpose, we used a set of daily meteorological data, collected from January 1, 1976, to December 31, 2014. Daily ET0 values were estimated by the FAO's Penman-Monteith equation (ET0PM). The main statistical tests used were the nonparametric Mann-Kendall test, the Sen test to detect the magnitude of the trend, and the Pettitt test to detect the start of the trend. For all tests, statistical significance was 5% and/or 1%. Analysis of variance (ANOVA) was also applied to identify significant differences between the mean interdecadal values for each season. The results showed a significant decreasing trend for ET0 in both Juazeiro (α = 5%) and Petrolina (α = 1%), with declines of 14.5 mm/year (Juazeiro) and 7.7 mm/year (Petrolina) and that this trend started in 1996. Probably, the ET0 decrease was associated with the increase in the irrigated agricultural areas, and the lake formed upstream from the areas by the construction of Sobradinho Dam. [ABSTRACT FROM AUTHOR]