In this article we describe natural hazards associated with outburst floods of Palcacocha Lake and landslide events on the slopes of its moraine dam, in Cojup Valley, Cordillera Blanca (Peru). These events occurred in the last 70 years and some of them resulted in disasters, which strongly affected the city of Huarás. Field investigations and reference expression hydrodynamic tests as well as archive satellite images and aerial pictures were used to describe the evolution of hazards connected with Palcacocha Lake. Expression hydrodynamic tests proved a high permeability of sandy gravels glacial sediments, which form the present-day lake dam. Seepage through the natural dam forming small ponds below the overflow spillways occurs. A retreat of the glacial tongue causing an increase of the lake volume and unloading of the slope toe areas are the most important recent processes that influence the potential hazards affecting the Cojup valley. The research has proved that the climate warming and ongoing deglaciation play a very significant role in the change of natural hazards conditions in high mountains.
Almost 40 glacial lakes have been remediated in the Cordillera Blanca since the 1940s by implementing different types of structural measures to prevent (mitigate) glacial lake outburst floods. These are (1) open cuts; (2) artificial dams; (3) tunnels; and their combinations. The first part of the paper provides an overview and description of the implemented remedial works. In the second part, the effectiveness of these remedial works is evaluated on the basis of a comparison of the quantified susceptibility of nine selected lakes to outburst floods before and after remediation. Our investigation showed that different types of remedial works have different impacts on the susceptibility of a given lake to outburst floods and are effective for different scenarios (causes and subsequent mechanisms) of outburst floods. Hazard management implications in the framework of risk management and ongoing geo‐environmental change are also discussed.
Les données hydrologiques (depuis 1953) du bassin versant de Llanganuco (87.0 km 2 , 39% glaciaire) montrent une accélération de la fonte glaciaire au dernier quart du 20ème siècle. Ces données sont complétées (depuis fin 2000) par celles du petit bassin de Artesoncocha (8.4 km 2 , 79% glaciaire). Leurs écoulements et les températures atmosphériques de réanalyse du NOAA-NCEP au-dessus de la Cordillère Blanche sont étroitement corrélés. Dès l'échelle mensuelle, les variations de la température sont un bon proxy de la fonte. Connus depuis plus de 50 ans, les reculs des glaciers de Cordillère Blanche montrent une accélération de la déglaciation au milieu des années 1970. Ces données de diverses origines permettent de modéliser la fonte des glaciers et de prévoir son évolution. Ajustées sur la période 1950-2000, les prévisions du modèle sont optimistes et en sous-estiment la rapidité si le changement climatique s'accélère. Le forçage du modèle par des prévisions d'évolution des températures, fournies par une adaptation à la Cordillère Blanche des modèles globaux du changement climatique, précise ces prévisions jusqu'alors basées sur le seul comportement passé des glaciers. Mots clefs bassins glaciaires tropicaux; changement climatique; Cordillère Blanche; fonte des glaciers; hydrologie glaciaire; lame écoulée; ressources en eau; taux d'englacement; températures atmosphériques de réanalyse NOAA-NCEP; Pérou
For the past 30 years, a process of glacier retreat has been observed in the Andes, raising alarm among regional water resources managers. The purpose of this paper is to develop a model of the role of Andean glaciers in the hydrology of their associated watersheds, which is appropriate for application at a river basin scale, with an eye towards creating an analytical tool that can be used to assess the water management implications of possible future glacier retreat. While the paper delves deeply into our formulation of a glacier module within a water resources management modelling system, the widely subscribed Water Evaluation and Planning System (WEAP), the originality of our work lies less in the domain of glaciology and more in how we apply an existing reduced form representation of glacier evolution within a model of the climate-glacier-hydrology-water management continuum. Key insights gained pertain to appropriate ways to deploy these reduced form representations in a relatively data poor environment and to effectively integrate them into a modelling framework that places glaciers within a wider water management context. The study area is the Rio Santa watershed in Peru which contains many of the expansive glaciers of the singular Cordillera Blanca. The specific objectives of this study included: (i) adequately simulating both monitored glacier retreat and observed river flows from the last forty years using historical climate time series as model input; (ii) quantifying the proportion of river flow in the Rio Santa produced from melting glaciers during this period; (iii) estimating the historical contribution of groundwater accretions to river flows; and (vi) reproducing a reasonable simulation of recent hydropower operations in the Rio Santa system. In pursuit objective (i), a split sample calibration-validation of the model was conducted by comparing the simulated glacier area to Landsat images taken in 1987 and 1998 and observed and simulated river flow at 16 control points in the Rio Santa watershed. At the global scale of the watershed, the glacier retreat is correctly simulated for the period 1970/1999 with a calculated retreat equals to −23% when the observed retreat is of −24%. Having established that the model can respond to these scientific objectives, the ultimate goal of the study was to demonstrate how this integrated modelling system can be used as a decision support tool to assist in planning water management adaptation to climate change. This sort of integrated assessment is required to adapt water resources management in the Andes to a~range of future climatic conditions, improving the resilience of developing Andean economies such Peru's in the face of a major drive of global change
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