Streamflow and precipitation trends in the Brazilian Amazon basin and their association with Pacific decadal oscillation and deforestation

The Amazon Basin is the region with the highest continental water density in the world and plays an important role in the global hydroclimatic system and the carbon cycle. In recent decades, the Amazon Basin has seen intense land use and land cover change (LULCC), specifically in terms of the conversion of rainforest into crop and livestock areas. The feedback mechanisms between the surface and atmosphere have been modified and biodiversity has also been endangered. In order to establish the long-term hydrological trends across the Amazon Basin and possible relationships with LULCC, monthly data on streamflow and precipitation obtained from surface stations and remote sensing of deforestation information from 1976 to 2010 were analyzed. Homogeneous streamflow sub-regions were determined, and assessments of these sub-regions show distinct patterns: while the trend for both rainfall and streamflow is positive in the northern basin, in the North and Amazon-Mouth sub-regions, the trend is negative for both variables in the southern basin, the West, South, and Central sub-regions. In the regions with a negative trend, the yearly deforestation rate presented high values, indicating the possible influence of LULCC on the Amazon’s hydrological cycle. Seasonal analysis shows that the reductions in streamflow and rainfall rates in the southern Amazon Basin were more frequently registered at the end of the dry season, indicating a prolonging of this season. Analysis with Global Precipitation Climatology Centre (GPCC) linear trend data relating the positive peak of Pacific decadal oscillation (PDO) to the negative period shows that the negative trend for rainfall and streamflow in the South sub-region is more intense than the influence of PDO. This reinforces the hypothesis that deforestation may be influencing the hydrological cycle in the Amazon Basin.