Changes in atmospheric moisture transport over tropical South America: an analysis under a climate change scenario

Abstract

Warming induced by increased greenhouse gas emissions is intensifying the global water cycle and increasing the water vapor content of the global atmosphere. However, there is a lack of scientific literature assessing how regional atmospheric moisture transport and recycling will change in a warming climate. This work analyzes the projections of atmospheric moisture transport and recycling over tropical South America by the end of the twenty-first century (2070–2100) under a climate change scenario (RCP8.5). We used the Dynamic Recycling Model to estimate atmospheric moisture contributions to the region considering input data from the European Centre for Medium-Range Weather Forecasts ERA5 reanalysis and 11 models included in the Fifth Phase of the Coupled Model Intercomparison Project. Projected increases of precipitable water in tropical South America are linked with increased evaporation from the oceans. However, those projections also indicate (1) reductions in the precipitation contributed by the main atmospheric moisture sources to the continental regions of tropical South America, (2) reductions of total precipitation, and (3) reductions of recycled precipitation over the region. The largest reductions of precipitation recycling are projected over the southern Amazon during the dry-to-wet transition season (about 31%) and the northern Amazon during its dry season (about 25%). This is particularly relevant since the southern Amazon has experienced the occurrence of longer dry seasons during the recent decades and has been highlighted as a hotspot of climate change.

Global terrestrial moisture recycling in Shared Socioeconomic Pathways

“…For the Amazon as a whole, the effects of deforestation on moisture recycling seem to be overshadowed by those of increasing atmospheric CO2 concentrations, although in terms of recycling ratios, the larger deforestation in SSP3-7.0 compensates for the stronger radiative forcing in SSP5-8.5. This is consistent with results from CMIP5 models, where every 10% of the basin deforested leads to an average precipitation decline of only 1.6% (Spracklen 430 and Garcia-Carreras, 2015), and where severe climate change (RCP8.5) leads to increased moisture influx from the Atlantic into South America, but reduced precipitation (recycling) over the Amazon (Arias et al, 2023). The comparatively small effect of deforestation is further confirmed by experiments using a range of CMIP6 models, where one study found that warming, via atmospheric circulation changes, accounts for 55% of Amazon drying under SSP3-7.0 conditions.…”

Orinoco revisited: Comprehensive analysis of the Orinoco River basin present and future hydroclimate

“…This result agrees with the projections of reductions higher than 35% reported by Brêda et al (2020) for northern South America based on CMIP5 GCMs. Those reductions of almost half of the precipitation around the year in the region, also reported by Arias et al (2023), added to the ongoing trend of deforestation in the Guianese rainforest, could enhance the severity of droughts in the basin (Sorí et al, 2023) and accelerate the savannisation of the region (Valencia et al, 2023). These alterations could lead to a reduction of the water vapor flux from the Atlantic Ocean towards the Amazon basin (Nieto et al, 2008;Bovolo et al, 2018) that transit through the Orinoco River basin; a reduction of the outflow of precipitation from the Orinoco basin towards Northern South America via moisture recycling (Hoyos et al, 2018;Escobar et al, 2022); extreme precipitation events (Martínez et al, 2023), or even the role of Central America as an evaporative source (Durán-Quesada et al, 2017).…”

Reply on RC1

“…However, they did not differentiate among different SSPs. Baker & Spracklen (2022) and Arias et al (2023) used Earth System Models to study changes in moisture recycling for particular 530 regions.…”