Relationship Between the Water Vapor Transport from the Amazon Basin and the Rainfall Regime over a Watershed on Brazil’s Southern Border

The climate of the south of Brazil is characterized by northern winds in a hegemonic way for the transfer of moisture. Thus, the goal here is to verify the impact of the meridional water vapor transport on the rainfall of the Mirim–São Gonçalo Watershed (MSGW), located in the extreme south of Brazil and essential for regional development. The study is based on the precipitation data from MSGW weather stations and ERA5 reanalysis data for the period 1981–2020, which allowed the analysis of the interactions between different climatological variables. The water vapor transport was analyzed using the vertically integrated water vapor flux (VIVF). Coefficients were obtained according to the VIVF values in two locations placed between the Amazon basin and southern Brazil, namely in Bolivia and Paraguay. The results show that the MSGW is directly impacted by moisture transport from the north in all seasons, and this transport is most significant at the 850 hPa level. In addition, the moisture and rainfall in the MSGW are also influenced by changes in the magnitude and direction of this flow, with an increase in transport in periods of El Niño, especially during spring. Therefore, the study brings insights into how changes in tropical South American climate, through a cascading effect, may affect the Mirim–São Gonçalo Watershed development in the middle latitudes from changes in the meridional water vapor transport, highlighting the importance of studying the tropical and extratropical interactions in South America for the MSGW management and sustainable development.