Investigating Land Surface Effects on the Moisture Transport over South America with a Moisture Tagging Model

Land-atmosphere interactions are a critical component of precipitation processes within the Amazon basin and La Plata River basin (LPRB) in South America. Two of the possible pathways through which the land surface can affect precipitation are 1) by changing the amount of moisture available for precipitation (moisture recycling) and 2) by changing the atmospheric thermal structure and consequently affecting circulation patterns. In this study, the Weather Research and Forecasting (WRF) Model with embedded water vapor tracers (WVT) is used to disentangle these relative contributions, with a particular focus on the precipitation of LPRB. Using WRF-WVT we track the moisture that originates from the Amazon basin over a 10-yr period. It is estimated that Amazon evapotranspiration (ET) contributes to around 30% of the total precipitation over the Amazon and around 16% over the LPRB. Focusing on large-scale circulation patterns that transport moisture into the LPRB, we show that land surface conditions in northwestern Argentina are critical for the meridional transport of moisture to higher latitudes via Chaco jet events (CJEs). Warm surface air temperature associated with dry soil moisture over northwestern Argentina is linked to enhanced CJE northerly low-level winds that intensify moisture transport by changing continental-scale circulation patterns. WRF sensitivity tests confirm that soil moisture variations over this region affect meridional moisture transport.