Precipitation patterns over northern Brazil basins: climatology, trends, and associated mechanisms

Abstract

In recent decades, the climate in North and Northeast Brazil has undergone significant changes, which indicate potential risks for water and food security due to increasing temperatures, changing precipitation patterns, and greater frequency of some extreme events. For example, there is evidence of changes in the strength of the hydrological cycles on North and Northeast Brazil river basins, but the magnitude and extension of the precipitation changes are highly dependent on the precipitation dataset under consideration and the methodology. Here, we analyze the precipitation trends in North and Northeast Brazil hydrological basins and the possible associated mechanisms and present the rainfall climatological cycles in these basins using multi-datasets. The results showed that, in most river basins, there is a clear distinction between the rainy and dry seasons, with a contrast between the basins of the North (which receive a higher amount of rainfall) and the Northeast Brazil (with low rainfall volume, especially in the Parnaíba and Eastern Northeast Atlantic basins). Moreover, the annual rainfall has undergone an increasing trend in western Brazil river basins and a decreasing trend in the eastern. This east–west dipole is associated with the strengthening (weakening) of the Walker and Hadley circulations in western (eastern) Brazil in recent decades. A multidecadal variability is seen to modulate the precipitation changes, which is in phase with the AMO cycle. CMIP6 detection and attribution experiments showed that both natural and anthropogenic factors can play a role in the recent changes observed in northern Brazil river basins.