Abstract
We evaluate the performance of a large ensemble of Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) over South America for a recent past reference period and examine their projections of twenty-first century precipitation and temperature changes. The future changes are computed for two time slices (2040–2059 and 2080–2099) relative to the reference period (1995–2014) under four Shared Socioeconomic Pathways (SSPs, SSP1–2.6, SSP2–4.5, SSP3–7.0 and SSP5–8.5). The CMIP6 GCMs successfully capture the main climate characteristics across South America. However, they exhibit varying skill in the spatiotemporal distribution of precipitation and temperature at the sub-regional scale, particularly over high latitudes and altitudes. Future precipitation exhibits a decrease over the east of the northern Andes in tropical South America and the southern Andes in Chile and Amazonia, and an increase over southeastern South America and the northern Andes—a result generally consistent with earlier CMIP (3 and 5) projections. However, most of these changes remain within the range of variability of the reference period. In contrast, temperature increases are robust in terms of magnitude even under the SSP1–2.6. Future changes mostly progress monotonically from the weakest to the strongest forcing scenario, and from the mid-century to late-century projection period. There is an increase in the seasonality of the intra-annual precipitation distribution, as the wetter part of the year contributes relatively more to the annual total. Furthermore, an increasingly heavy-tailed precipitation distribution and a rightward shifted temperature distribution provide strong indications of a more intense hydrological cycle as greenhouse gas emissions increase. The relative distance of an individual GCM from the ensemble mean does not substantially vary across different scenarios. We found no clear systematic linkage between model spread about the mean in the reference period and the magnitude of simulated sub-regional climate change in the future period. Overall, these results could be useful for regional climate change impact assessments across South America.
Highlights
Precipitation patterns generally exhibit a northwest-southeast orientation over the continent due to the South Atlantic Convergence Zone (SACZ; Silva Dias and Carvalho 2017; Llopart et al 2020a), which is the main feature of the South American Monsoon System (SAMS) variability over tropical South America in its wet season
Over South America, the Andes play an important role in maintaining the South American Low-Level Jet (SALLJ) on their east, which is an important mechanism for transporting warm and moist air from the tropics to the subtropics (Vera et al 2006; DossGollin et al 2018; Montini et al 2019; Kumar et al 2020; Chavez et al 2020)
During October to March, the SAMS develops over the continent and leads to a broad maximum of precipitation stretching from western Amazonia to southeastern Brazil (> 9 mm/day) (Fig. 2d, e)
Summary
Like many other regions across the planet, South America has experienced environmental changes during the twentieth century, including increasing surface temperatures (Salviano et al 2016; de Barros Soares et al 2017; Dereczynski et al.Extended author information available on the last page of the article2020; Pabon-Caicedo et al 2020), shifting precipitation patterns (Espinoza et al 2019; Paca et al 2020; Marrafon et al 2020; Carvalho 2020; Giráldez et al 2020; Pabon-Caicedo et al 2020), vanishing Andean glaciers (Schauwecker et al 2014; Malmros et al 2016; Drenkhan et al 2018; Vuille et al 2018; Somers et al 2019; Masiokas et al 2020), and an increase in weather and climate extremes, such as droughts, floods, and wildfires (Barros et al 2015; Martins et al 2018; Viganó et al 2018; Cunha et al 2019; Feron et al 2019; Lemes et al 2020; Debortoli et al 2020; Zubieta et al. Vol.:(0123456789)2021). Over the past several decades, it is feared that human-induced changes have contributed to reduced rainfall over parts of the Amazon, increasing the vulnerability of its ecosystem to droughts and wildfires (Brando et al 2014, 2019; Boisier et al 2015; Duffy et al 2015; De Faria et al 2017; Silva et al 2018; Marengo et al 2018; Barkhordarian et al 2019; Cook et al 2020; Parsons 2020) and threatening the delicate balance of the Earth System. Changing climate patterns may have a significant role in soil degradation and desertification—an issue faced by several countries across the continent (Spinoni et al 2015; Pérez et al 2017; Vieira et al 2021)—which has serious consequences for social-ecological sustainability and food security
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