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Item type:Publication, 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). - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Performance of regional climate model precipitation simulations over the terrain-complex Andes-Amazon transition region(John Wiley and Sons Inc, 2024-01-16)Regional climate models (RCMs) are widely used to assess future impacts associated with climate change at regional and local scales. RCMs must represent relevant climate variables in the present-day climate to be considered fit-for-purpose for impact assessment. This condition is particularly difficult to meet over complex regions such as the Andes-Amazon transition region, where the Andean topography and abundance of tropical rainfall regimes remain a challenge for numerical climate models. In this study, we evaluate the ability of 30 regional climate simulations (6 RCMs driven by 10 global climate models) to reproduce historical (1981–2005) rainfall climatology and temporal variability over the Andes-Amazon transition region. We assess spatio-temporal features such as spatial distribution of rainfall, focusing on the orographic effects over the Andes-Amazon “rainfall hotspots” region, and seasonal and interannual precipitation variability. The Eta RCM exhibits the highest spatial correlation (up to 0.6) and accurately reproduces mean annual precipitation and orographic precipitation patterns across the region, while some other RCMs have good performances at specific locations. Most RCMs simulate a wet bias over the highlands, particularly at the eastern Andean summits, as evidenced by the 100%–2,500% overestimations of precipitation in these regions. Annual cycles are well represented by most RCMs, but peak seasons are exaggerated, especially at equatorial locations. No RCM is particularly skillful in reproducing the interannual variability patterns. Results highlight skills and weaknesses of the different regional climate simulations, and can assist in the selection of regional climate simulations for impact studies in the Andes-Amazon transition zone. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Recent progress in atmospheric modeling over the Andes – Part II: Projected changes and modeling challenges(Frontiers Media SA, 2024-01-01)In the Andes, the complex topography and unique latitudinal extension of the cordillera are responsible for a wide diversity of climate gradients and contrasts. Part I of this series reviews the current modeling efforts in simulating key atmospheric-orographic processes for the weather and climate of the Andean region. Building on this foundation, Part II focuses on global and regional climate models challenging task of correctly simulating changes in surface-atmosphere interactions and hydroclimate processes to provide reliable future projections of hydroclimatic trajectories in the Andes Cordillera. We provide a review of recent advances in atmospheric modeling to identify and produce reliable hydroclimate information in the Andes. In particular, we summarize the most recent modeling research on projected changes by the end of the 21st century in terms of temperature and precipitation over the Andes, the mountain elevation-dependent warming signal, and land cover changes. Recent improvements made in atmospheric kilometer-scale model configurations (e.g., resolution, parameterizations and surface forcing data) are briefly reviewed, highlighting their impact on modeling results in the Andes for precipitation, atmospheric and surface-atmosphere interaction processes, as mentioned in recent studies. Finally, we discuss the challenges and perspectives of climate modeling, with a focus on the hydroclimate of the Andes. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Recent changes in the dry-to-wet transition season in the Andean Altiplano and related atmospheric circulation patterns (1981–2022)(Springer Science+Business Media, 2025-01-01)Drought-related impacts in the southern Tropical Andes are crucial for economic activities. Here, precipitation decreases (p < 0.1) during the dry-to-wet transition season (SON) based on CHIRPS (1981–2023) and meteorological stations (1973–2016). In addition, a decline in specific humidity and moisture flux is detected (1979–2022). The precipitation trend is stronger (p < 0.05) in the southern Titicaca, Desaguadero, Poopó and Coipasa Salt Pan hydrological system (TDPS) and extends southwards (20°S-30°S). A delayed onset and a reduced duration of the wet season are observed in the TDPS (p < 0.05), although precipitation intensifies during DJF in the southwestern TDPS (p < 0.05).To analyze the atmospheric features related to these changes, we derive atmospherics circulation patterns (CPs) from standardized anomalies of daily 200-hPa winds (1979–2022) using a weather classification technique. We identify 9 CPs, characterized by four ‘‘dry’’ (D1, D2, D3, and D4), three ‘‘wet’’ (W1, W2 and W3), and two ‘‘transitional’’ patterns (T1 and T2). During SON, the frequency of the W1 (D3) is negatively (positively) correlated with the onset date of the wet season (p < 0.05). Through the period 1979–2022, the frequencies of the D3 and the predominantly dry T1 increase (p < 0.1 and p < 0.05, respectively). Conversely, W1 frequency diminishes substantially since 2010. The physical mechanisms associated are discussed. In conclusion, increased D3 and T1 frequencies, and decreased W1 are related to the diminution of precipitation during SON and to the shortening of the wet season length. We also show that the extreme drought of 2022 was characterized by an unprecedented frequency of dry CPs, particularly during November.2 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Impacts of the future Amazon deforestation on the precipitation over the Peruvian central Andes and related atmospheric features(Elsevier BV, 2026-10-01)This study investigates the impact of a 40% Amazon deforestation scenario (projected for 2050) on precipitation over the central Peruvian Andes during five austral summer seasons (DJF 2001–2006) using high-resolution (1 km) WRF simulations. While a widespread rainfall reduction pattern is observed over the Amazon-Andes transition zone, statistically significant decreases ( p < 0.10) at the gridpoint level are primarily concentrated near rainfall hotspots in the Amazon-Andes transitions zone, reaching an average reduction of 12% (−1.4 mm day −1 ). This drying signal is physically associated with a weakening of the South American Low-Level Jet (LLJ) and reduced moisture influx, which specifically inhibits convective activity during the morning peak hours (23–11 LT). In the high-altitude Mantaro Basin, we observe a consistent drying pattern (−5%) that extends from the transition zone; although these changes are not statistically significant due to high interannual variability, the physical signal of precipitation reduction and dry air advection remains clear. Conversely, the western Andean ridges exhibit a localized precipitation increase (up to 20%) linked to intensified cross-barrier easterly wind anomalies reinforcing diurnal anabatic circulation. We further find that while 5 km resolution captures broad basin-scale patterns, convection-permitting scales (1 km) are essential for resolving these complex topographic effects. These findings highlight a critical vulnerability concentrated along the eastern slopes and the high Andes. The identified drying patterns, which are particularly pronounced in the Andes-Amazon transition zone (a global biodiversity hotspot) and extend into the highlands, pose a significant threat to endemic ecosystems and regional water security, specifically through reservoir inflow reduction and negative impacts on agriculture.1 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, 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.2