The Influence of the Amazonian Moisture Transport by the Aerial Rivers to the Water Budget at Southeastern Brazil Using Atmospheric Modelling and Re-analysis

The moisture transport from Amazon forest is a great moisture source for the regional water cycle in South America (SA), especially at southeast and southern part including Parana and La Plata Basins. Several previous studies have shown this importance and how anthropic processes of either global warming and/or Amazon deforestation may affect this Amazonian moisture by the aerial rivers. The new advances in the parameterization of the microphysics (for instance using the convective permitting models) allow improvements in the water representation in varying timescales. So, in order to do this study, we have used 2 data-set from Amazonia: a) the Meteorological Office Unified Model (UM) simulations for 4.5 and 25 km horizontal resolutions; b) the ERA5 reanalysis (vertical profiles of windspeed and specific humidity). The period used in these analysis were from 1998-2007 during the austral summer (months from December up to February). The moisture transport was computed from the surface up to middle troposphere (500 hPa) using IVT definitions. We selected 2 boxs domains: one in the Amazon basin and the other in the Brazilian southeast region (named Sao Paulo) in order to identify the moisture’s output and input for water budget. The results showed some precipitation bias, mainly in the central/south Amazon basin (~ +2.5 mm.day^-1) and in Sao Paulo +1.5 mm.day^-1). Some similarities were identified between 4.5 km and observations (ERA5) vertically integrated moisture flow patterns for Amazon basin as well as northern Sao Paulo area (-7% and -13%, respectively). On the other hand, the 25 km simulation underestimated the intensity of fluxes in the whole pathway by 4.5%, which represents -6.9 kg m^-1 s^-1. The low water transport was explained by some reduction on the vertical moisture transport, mainly between 700 and 500hPa (~ -3.2 kg m^-1 s^-1 in the Amazon southern area and -2.5 kg m^-1 s^-1 in Sao Paulo area). Despite some biases identified, the differences compared to ERA5 data are small, indicating that convection-permitting models offer valuable insights for better understanding regional climate connections, albeit their elevated computational costs.