Observed and Projected Hydroclimate Changes in the Andes

Abstract

The Andes is the most biodiverse region across the globe. In addition, some of the largest urban areas in South America are located within this region. Therefore, ecosystems and human population are affected by hydroclimate changes reported at global, regional and local scales. This paper summarizes progress of knowledge about long-term trends observed during the last two millennia over the entire Andes, with more detail for the period since the second half of the 20th century, and presents a synthesis of climate change projections by the end of the 21st century. In particular, this paper focuses on temperature, precipitation and surface runoff in the Andes. Changes in the Andean cryosphere are not included here since this particular topic is discussed in other paper in this Frontiers special issue, and elsewhere (e.g. IPCC, 2019b). While previous works have reviewed the hydroclimate of South America and particular sectors (i.e., Amazon and La Plata basins, the Altiplano, Northern South America, etc.) this review includes for the first time the entire Andes region, considering all latitudinal ranges: tropical (North of 27 • S), subtropical (27 • S−37 • S) and extratropical (South of 37 • S). This paper provides a comprehensive view of past and recent changes, as well as available climate change projections, over the entire Andean range. From this review, the main knowledge gaps are highlighted and urgent research necessities in order to provide more mechanistic understanding of hydroclimate changes in the Andes and more confident projections of its possible changes in association with global climate change. Keywords: hydroclimate of the Andes, global change in the Andes, hydroclimate trends in the Andes, hydroclimate projections of the Andes, climate change in the Andes, climate change scenarios for the Andes

Colombian climatology in CMIP5/CMIP6 models: Persistent biases and improvements

“…projections for air surface temperature) shows agreement on the warming signal over the entire region, although temperature increases are lower than for the CMIP6 ensemble (Figure 6d). The projections toward warmer temperatures in Colombia under high GHG emission scenarios have also been reported from CMIP5 models [19][82] [83][84] [85].…”

“…Although CMIP5 and CMIP6 models improved their simulations of global climate with respect to the previous generations, they still exhibit systematic biases and uncertainties [7] [11] [12] [13] [14]. In particular, these models exhibit larger biases for precipitation than air surface temperature simulations not only at global [7] [13] but also at regional scale in northern South America, including Colombia [15] [16] [17] [18] [19] [20]. In particular, the effects of clouds and aerosols and their interactions are among the causes for these persistent biases [7] [13] [21] [22].…”

“…[23][25][26] [52][53] [54][55] [56][57] [58]). Due to the interactions among such variety of phenomena, CMIP models have large biases simulating precipitation in the Andes, particularly in Colombia [16] [17] [18] [19] [20]. Among these different biases, CMIP models exhibit a systematic bias, known as the Double-ITCZ bias, which has persisted among all generations of CMIP5 models, including CMIP6, affecting the representation of precipitation in regions like Colombia [7][11] [13] [15][17] [20][21] [34].…”

Hydrological droughts in the southern Andes (40–45°S) from an ensemble experiment using CMIP5 and CMIP6 models

“…This trend has favored dry conditions, mainly during the summer and autumn seasons (December to April) in the southern Andes 3 (40–45°S). Dendrochronological reconstructions have shown that the present trend of the SAM is unprecedented in the last six centuries 11 , which has been evident in the precipitation and temperature of the southern Andes 12 , 13 . The trend towards a drier and warmer climate has also increased the climatic synergy with El Niño-Southern Oscillation (ENSO), promoting conditions of severe and extensive droughts 14 .…”

“…Climate projections in the Southern Andes suggest a prolongation of the dry conditions that have affected them over the past decades 12 . General Circulation Models (GCMs) from the Coupled Model Intercomparison Project (CMIP) phase 5 indicate a latitudinal pattern of decreasing precipitation that intensifies towards the central Andes, while temperature increases mostly on the eastern slopes of the Andes 12 . The new generation of CMIP6 models has improved in many aspects.…”