Land-Atmosphere Interactions over Southern South America and Their Links to Extreme Convective Systems (Invited Presentation)

Some of the world’s deepest and largest convective storms develop in South America’s La Plata River basin. Mesoscale convective systems (MCS) often develop along the mountainous terrain and migrate east as they organize into large systems with broad convective cores and intense precipitation. This region is also a “hot spot” for land-atmosphere interactions. Soil moisture is strongly coupled with precipitation in the northern part of the La Plata basin, and a significant amount of precipitation originates from terrestrial evapotranspiration throughout the region.

In this work, we evaluate the different ways that the land surface affects hydroclimate over the region – from the local to the continental scale. Using the regional climate model WRF with the added capability of water vapor tracers, we show that moisture from the Amazon basin contributes to about 16% of the precipitation over the La Plata basin. The Chaco Low Level jet (CLLJ) enables the transport of this moisture into the southern part of the continent. This jet is linked to deep moist convection and MCSs over southern South America. We find that large-scale land surface conditions affect the strength of the CLLJ. Antecedent conditions for the CLLJ are characterized by a wetter-than-average northern La Plata, and drier than average southern La Plata.

The model-based study is further corroborated by an observational study of the effect of vegetation on the climate of the region using remote sensing and the generalized feedback assessment (GEFA) statistical technique. The analysis reveals that the dominant mode of variability in the vegetation is also a dipole analogous to our model results, with greener conditions in the northern La Plata and browner conditions in the southern La Plata. This vegetation mode is linked to stronger precipitation throughout the basin. In summary, our work highlights well-known and new mechanisms by which the land surface can affect extreme precipitation in southern South America.