On the Hydrological Cycle of the Amazon Basin: a Historical Review and Current State-of-the-art

This paper constitutes a review on the history and current state-of-the-art on studies of the hydrological cycle and estimates of the components of the water balance in the Amazon Basin. Since the 1970’s, various papers started to discuss the issues of water balance and moisture transport in the region, using simple models and meteorological data from reduced surface and upper air observational network in the basin, and using river data from the Amazon River and its major tributaries. The availability of gridded rainfall data sets and the global reanalysis have allowed for more comprehensive studies on regional water balance in a regional scale, as well as its variability and long term tendencies. The importance of the role of evapotranspiration from the forest in the regional precipitation and recycling was introduced during the second half of the 1970’s, and this was important to prove the hypothesis that increased deforestation in the region would drastically change the water cycle and therefore the climate on the region and in the planet. This resulted on numerous experiments on Amazon deforestation and its impacts on climate since the 1980’s, and more complex models and representations on the dynamics of vegetation on regional climate have allowed to more realistic simulations of climate change due to changes in land use and in the concentration of greenhouse gases on the recent years. This paper makes a critical review of previous studies on the issues of the hydrological cycle change and estimates of the water balance components in the basin and their time and space variability, the role of recycling of precipitation in the basin, the role of the Amazon as a source of moisture for regions such as the La Plata Basin. One important aspect to discuss are the possible impacts of deforestation and land use changes in future climate and hydrology in the basin, as well as in the moisture transport to other regions where the hydrological cycle depends on the moisture exported from the Amazon region.