Mapping the Hydrologic Response of the Brazilian hydrologic regions and their variability associated with El Niño and La Niña

Abstract

Brazil has a wide-ranging network of rivers flowing northeast, east, north or southward. The water running off these basins may vary a great deal with climate and spatial distribution of rainfall rates. This paper analyzes the Hydrological Response (HR) of the eight major Brazilian river basins and sub-basins for a period matching 30 years of data, from 1970 to 2000. HR refers to river flow normalized by rainfall over the basin. The atmospheric forcing strongly modulates the HR at synoptic scales. At local scales, geology and land use also play an important role. The average spatial HR reached values as high as 0.7 in the west of Brazilian Amazon. We estimated “average” to “high” values in central and western Amazon (0.3-0.5) and “average” in the center-south and southeast (around 0.3). We found HR in the northeast semi-arid of Brazil classified as “very low” (close to 0.1). Brazil has climates changing from humid and rainy to semi-arid regions. Besides analyzing the regional distribution of the HR across the country, we explored the effects of the interanual variability associated with ENSO and La Niña. We used the normal climate average over thirty years as the standard for comparing the differences associated with the two anomalies. We noticed that the subbasins of the southern regions showed positive variations in water production while the Brazilian Amazon basin showed no response. Also, the areas of lower HR in the northeast Brazil were further reduced.