On the importance of cascading moisture recycling in South America

Abstract

Abstract.Continental moisture recycling is a crucial process of the South American climate system. In particular, evapotranspiration from the Amazon basin contributes substantially to precipitation regionally as well as over other remote regions such as the La Plata basin. Here we present an indepth analysis of South American moisture recycling mechanisms. In particular, we quantify the importance of cascading moisture recycling (CMR), which describes moisture transport between two locations on the continent that involves reevaporation cycles along the way. Using an Eulerian atmospheric moisture tracking model forced by a combination of several historical climate data sets, we were able to construct a complex network of moisture recycling for South America. Our results show that CMR contributes about 9-10 % to the total precipitation over South America and 17-18 % over the La Plata basin. CMR increases the fraction of total precipitation over the La Plata basin that originates from the Amazon basin from 18-23 to 24-29 % during the wet season. We also show that the south-western part of the Amazon basin is not only a direct source of rainfall over the La Plata basin, but also a key intermediary region that distributes moisture originating from the entire Amazon basin towards the La Plata basin during the wet season. Our results suggest that land use change in this region might have a stronger impact on downwind rainfall than previously thought. Using complex network analysis techniques, we find the eastern side of the sub-tropical Andes to be a key region where CMR pathways are channeled. This study offers a better understanding of the interactions between the vegetation and the atmosphere on the water cycle, which is needed in a context of land use and climate change in South America.

Why does Amazon precipitation decrease when tropical forests respond to increasing CO2?

“…2b) decreases everywhere there is vegetation. This decrease is important over the Amazon basin, where precipitation recycling via evapotranspiration is important [e.g., Zemp et al, 2014;Staal et al, 2018] and where decreased moisture flux to the atmosphere will affect the moisture supply available to convection and precipitation. This decrease in transpiration is associated with a diminished latent cooling at the surface ( Fig.…”

“…In addition, precipitation recycling (i.e., the cascade of moisture through precipitation, evapotranspiration, and subsequent precipitation cycles)-especially during the dry season-is a critical source of moisture for the interior rainforest and is estimated to contribute 20-30% of rainfall over the Amazon basin [Brubaker et al, 1993;Eltahir and Bras, 1994;Lee et al, 2005;Van der Ent et al, 2010;Zemp et al, 2014;Staal et al, 2018]. Canopy evapotranspiration is also influential in the dry-to-wet transition season, moistening the lower and middle atmosphere in the months leading up to the monsoon and priming the troposphere for deep convection [Wright et al, 2017].…”

New Insights on Land Surface-Atmosphere Feedbacks over Tropical South America at Interannual Timescales

“…Besides, these LAFs have been studied for annual and intra-annual timescales, but the interannual timescale has also been largely overlooked. Most of the research at the interannual timescale has been focused on the study of large-scale atmospheric teleconnections or anomalies in the transport of moisture by winds [2,31,33,62], but the role of LAFs has not been thoroughly explored. We explored land surface-atmosphere feedbacks at interannual timescales using mainly a simplified overview of connectivity of the most relevant variables that describe these interactions as well as identifying the regions of TropSA where they are best characterized.…”

Brazil’s Amazonian forest carbon: the key to Southern Amazonia’s significance for global climate

“…Brazil's Southeastern region (including São Paulo) and neighboring countries are major recipients of this transport (Arraut et al 2012). The La Plata Basin is estimated to depend on water-vapor transport from Amazonia for 70 % of its annual total precipitation (van der Ent et al 2010), and this water source is especially dominant in the Austral summer (Zemp et al 2014). Water transport therefore represents a second important category of environmental service.…”