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Subject: search.filters.subject.South American Altiplano

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    The 2022–23 drought in the South American Altiplano: ENSO effects on moisture flux in the western Amazon during the pre-wet season
    (Elsevier B.V., 2024-09-01)
    The 2022-23 hydrological year in the Lake Titicaca, Desaguadero River, and Lake Poopó hydrological system (TDPS) over the South American Altiplano constituted a historically dry period. This drought was particularly severe during the pre-wet season (October–December), when the TDPS and the adjacent Andean-Amazon region experienced as much as 60% reductions in rainfall. Consequently, Titicaca Lake water levels decreased by 0.05 m from December to January, which is part of the rising lake level period of normal conditions. Such conditions have not been seen since the El Niño-related drought of 1982-83. Using a set of hydroclimatic, Sea Surface Temperature (SST) and atmospheric reanalysis datasets, we find that this new historical drought was associated with enhanced southerly moisture flux anomalies, reducing the inflow of moisture-laden winds from the Amazon basin to the TDPS. Such anomalies in moisture transport were not seen since at least the 1950s. The atmospheric dynamics associated with this drought are related to La Niña SST anomalies via subtropical teleconnections associated with Rossby wave trains towards South America, further extended by subtropical Atlantic Ocean SST anomalies. This feature reduced the atmospheric moisture inflow from the Amazon and weakened the development of the Bolivian High in the upper troposphere. These results document a new atmospheric mechanism related to extreme droughts in the TDPS associated with La Niña SST anomalies during the pre-wet season. This goes beyond the traditional understanding of El Niño events, especially the strongest ones, being associated with dry conditions in the TDPS during the wet season (December–March).
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    Future projections of summer precipitation-driving mechanisms over the South American Altiplano
    (Springer Science+Business Media, 2025-03-01)
    The South American Altiplano, located in the central Andes between 15 and 22 ºS, stands out for its high altitude, reaching up to 3000 m above sea level (m.a.s.l.). Rainfall patterns in this area, with 70% occurring during the summer season (December to February), are vital for soil moisture recharge and sustaining life, vegetation, and agriculture during dry months. Therefore, projections of future precipitation changes are crucial for water management and related risks. However, General Circulation Models (GCMs) show unreliability in predicting precipitation over the region, with significant biases and uncertainty. This study aims to address this issue by analyzing projected changes in precipitation using mechanisms previously identified in the literature, like zonal winds at 200 hPa over the southern tropical Andes (U200 mechanism) and vertical motion at 500 hPa over the western Amazon (W500 mechanism). These mechanisms, derived from more reliable GCM variables such as winds, explain interannual precipitation variability over the Altiplano. By assessing 13 GCMs from the sixth phase of the Coupled Model Intercomparison Project (CMIP6), this study evaluates changes in precipitation over the mid-twenty-first century across historical (1980–2014) and future (2050–2084) periods under the SSP3-7.0 scenario. Results indicate successful models capture the relationship between U200, W500, and precipitation over the Altiplano, projecting a reduction of up to 35% when considering the U200 mechanism and 26% under the W500 mechanism. These reductions vary across the Altiplano, with the southern region experiencing the most significant projected decreases.
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