Analysis of atmospheric moisture transport to the Upper Parana River basin

摘要

The understanding of the atmospheric phase of the hydrological cycle is an important step forward in improving our abilities to predict droughts and floods, as well as the impacts of climate change on water resources. Here we focus on the study of the atmospheric moisture transport to the Upper Parana River basin, Brazil, through the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) dispersion model, which is used to generate air masses trajectories based on the 1970-2010 National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data. In terms of moisture source regions, we found that the tropical South Atlantic is the main contributor to the Upper Parana River basin, exporting about 175 mm/month of water vapour during the rainy season. The North Atlantic contribution is relevant in February (about 38 mm/month). Other regions over the Atlantic Ocean (North and subtropical South) are also identified as sources, and moisture evaporated from these places has a significant impact on the streamflow variability at the Itaipu streamflow gauge, located at the basin outlet. The continental sources play a more relevant role during the dry season (May-October). The Amazon region is more relevant as a moisture source during the dry season, exporting an average of 45 mm/month. A similar pattern is observed in other continental sources, such as Chaco/Pantanal/Cerrado, which together export about 99 mm/month to the Parana River basin during the dry season. An extreme event analysis reveals that changes in moisture advection from the tropical South Atlantic are related to floods and droughts in the region. Particularly, we observe that flood events are preceded by positive anomalies of moisture advection up to 2 months in advance, while persistent, negative anomalies of moisture transport lead seasonal droughts by up to 8 months beforehand.