Browsing by Autor "Tim Stott"

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Signals of an increasing drought condition in the Central Andes
(2025) Juliana Nogueira; Heitor Evangelista; Edson Ramírez; Newton de Magalhães Neto; Patricia Piacsek; Osama Mustafa; Ana Laura Navas Romero; Tim Stott; Bulat Mavlyudov; Gerd Dercon
<title>Abstract</title> The tropical glaciers of the Central Andes, particularly those in the Cordillera Real and surroundings, have been experiencing accelerated retreat since 1980. Dendrochronology based studies reach the same conclusions. These facts may profoundly impact communities living in the Andean high mountains and even in big cities like La Paz. This study examines the environmental changes in the Lake Tuni catchment and its associated glaciers (Condoriri, Jist'aña and Huayna-Potosí), located in the Cordillera Real Mountain range, 20-50 km northeast of La Paz. We employed a multi-proxy analysis based on the glacier´s dynamics, historical regional meteorological data, climate indices, and the geochemistry retrieved from a well-dated sedimentary record from Lake Tuni. The remote sensing data reveals a significant acceleration in glacier retreat beginning in the 1990s, with a pronounced worsening observed in the early 2000s while the sedimentary record shows a decline in runoff since 2000, characterized by a reduction in the terrigenous composition and magnetic susceptibility of sediments and a dominance of pollens of plants typical of drier conditions. Additionally, since the 1980s, increasing microcharcoal, dust, and wind-blown minerals from ice-free proglacial areas have darkened glacier surfaces, potentially accelerating melt. These indicators suggest a reduced availability of meltwater, which is critical for local water resources. Our findings imply that since the 1990s, the timing of glacier retreat has coincided with significant reductions in precipitation and changes in regional hydrology. We attribute these changes to altered Southern Amazon basin hydrology where vast areas of deforestation were created in the same period. This study highlights the extreme vulnerability of the Central Andes ecosystem, where the interplay and timing of climate change and land use by humans create unprecedented challenges. The continued retreat of these glaciers poses significant risks to water security for Andean communities, underscoring the urgent need for integrated, multidisciplinary approaches to enhance climate resilience in the region.
Signals of an increasing drought condition in the Central Andes
(2025) Juliana Nogueira; Heitor Evangelista; Edson Ramírez; Newton de Magalhães Neto; Patricia Piacsek; Osama Mustafa; Ana Laura Navas Romero; Tim Stott; Bulat Mavlyudov; Gerd Dercon
<title>Abstract</title> The tropical glaciers of the Central Andes, particularly those in the Cordillera Real and surroundings, have been experiencing accelerated retreat since 1980. Dendrochronology based studies reach the same conclusions. These facts may profoundly impact communities living in the Andean high mountains and even in big cities like La Paz. This study examines the environmental changes in the Lake Tuni catchment and its associated glaciers (Condoriri, Jist'aña and Huayna-Potosí), located in the Cordillera Real Mountain range, 20-50 km northeast of La Paz. We employed a multi-proxy analysis based on the glacier´s dynamics, historical regional meteorological data, climate indices, and the geochemistry retrieved from a well-dated sedimentary record from Lake Tuni. The remote sensing data reveals a significant acceleration in glacier retreat beginning in the 1990s, with a pronounced worsening observed in the early 2000s while the sedimentary record shows a decline in runoff since 2000, characterized by a reduction in the terrigenous composition and magnetic susceptibility of sediments and a dominance of pollens of plants typical of drier conditions. Additionally, since the 1980s, increasing microcharcoal, dust, and wind-blown minerals from ice-free proglacial areas have darkened glacier surfaces, potentially accelerating melt. These indicators suggest a reduced availability of meltwater, which is critical for local water resources. Our findings imply that since the 1990s, the timing of glacier retreat has coincided with significant reductions in precipitation and changes in regional hydrology. We attribute these changes to altered Southern Amazon basin hydrology where vast areas of deforestation were created in the same period. This study highlights the extreme vulnerability of the Central Andes ecosystem, where the interplay and timing of climate change and land use by humans create unprecedented challenges. The continued retreat of these glaciers poses significant risks to water security for Andean communities, underscoring the urgent need for integrated, multidisciplinary approaches to enhance climate resilience in the region.
The impact of glacier retreat on Andean high wetlands: Assessing the geochemical transfer and sediment provenance in the proglacial area of Huayna-Potosí (Bolivia)
(Elsevier BV, 2024) Ana Navas; Edson Ramírez; Leticia Gaspar; Iván Lizaga; Tim Stott; Francisco Rojas; Borja Latorre; Gerd Dercon
The accelerated decline of tropical Andean glaciers is affecting the water cycle of mountains in the region. In the Cordillera Real (Bolivia) on the Huayna-Potosí peak (6088 m a.s.l.), the rapid retreat of the Oeste Glacier is exposing new rock outcrops and glacial materials. Changes in the hydrological regime by glacier retreat are likely to modify the supply of sediments and subsequently affect the geochemical transfer of particle-bound elements within proglacial and downstream ecosystems. To address this issue, a sampling campaign in the proglacial area of Huayna-Potosí aimed to identify and collect sediments from the primary active landforms. To characterise elemental transfer and identify sediment provenance using fingerprinting techniques, streambed sediments were collected along the main stream from the glacier tongue at 5002 m a.s.l. to a wetland shallow lake at 4700 m a.s.l.. Geomorphological features control the production of fine particles and the distribution of particle-bound geochemical elements. Complex processes of solubilization, mobilisation, and retention govern the elemental transfer. Significant increases in 238U, as well as some major elements, were observed in the surface lake sediments, while Pb, Cr, and Cu decreased, and 137Cs was not detected. The spatial distribution patterns of geochemical elements and the assessment of the sediment provenance indicate that deglaciation fosters geochemical processes and the elemental transfer dynamics in the wetlands. Moraines and colluvium were found to be the primary contributors to sediment yield (93 %) while the rich organic soils in swamps contributed the least (7 %). The enhanced supply of sediments to the shallow lake in parallel to glacier decline may affect water quality and bring about further changes in the wetlands. Identifying primary sediment sources is essential for water management. Our findings enhance understanding of the compositional characteristics of mobilised sediment and their variations, aiding in more effective resource management to preserve these high-altitude wetlands.