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Climate-runoff relationship in the Andes of Ecuador, a case of study on Antizana stratovolcano

Congress: 2008
Author(s): Vincent Favier3, Eric Cadier2, Bernard Pouyaud1, Luis Maisincho4, Fanny Delachaux2, Diego Paredes5
1 IRD, Great Ice (UR IRD R032), Maison des Sciences de l’Eau, BP 64501, 34394 Montpellier, Cedex 5, France 2 IRD, Great Ice (UR IRD R032), Whymper 442 y Coruña, Casilla 17- 12-857, Quito, Ecuador 3 CEAZA, Benavente 980, casilla 599, La Serena, Chile 4 I

Keyword(s): climate, glacier runoff, water ressources, Ecuador, stratovolcano
AbstractIntroduction Demographic growth of cities like Quito (Ecuador) implies seek for new water sources. In mountainous regions of Ecuador some of them are located above 4000 m of altitude. Water resources from these areas are highly appreciated by users, due to their low rate of contamination and their high potential energy for electric production. Actually, many of these sources are partially fed by glaciers but this situation may change in the future. Aim The aims of this study are i) to quantify the water contribution from Antizana Glacier 12 to low altitude discharge and ii) to assess its variability as a response of climatic forcing. Methods Glacier mass losses of Antizana Glacier 12 over 2005-2006 period were estimated from monthly measurements performed on a network of ablation stakes located between 4750 m and 4950 m. These data were compared to runoffs measured downstream at 4500 m and 4000 m in order to establish the effective contribution of the glacier to water resources. Finally, meteorological measurements allowed to better understand the links between atmospheric conditions and glacier melt. Results and discussion At 4000 m, glacier contribution represented 25% of the available water resources of the catchment. Glacier contribution varied from 40% to 10% and suggests an effect of regulation by the glacier to the hydrological regime. Extrapolation of this result is hard because important groundwater flow has been observed at the same volcano on Glacier 15 (Favier et al., in press). This behavior has also been observed on glacier 12, but with less intensity. This result could imply a high spatial heterogeneity in terms of infiltration. Runoffs were compared to temperature data collected in the field and to reanalyzed wind speed at 500 hPa (77.5ºW0ºS). Under current climate conditions, an empirical approach on a monthly basis showed that 70% of runoff variance is explained by temperature and wind. The study of variables related to surface energy balance makes possible to explain the good quality of this relationship. Temperature is correlated with the energy balance terms and with melt, and wind is a good proxy of humidity availability. Low humidity conditions should strengthen sublimation. Wind is a better proxy of turbulent heat fluxes than humidity because humidity does not present strong intrannual variations within the inner tropics. Moreover, wind (proxy of humidity) is a good a proxy of cloudiness, and clouds play a strong role in the magnitude incoming solar and longwave radiations at the glacier surface, which are the main sources of energy for melt (Favier et al., 2004, Sicart et al., 2005). As a consequence, despite its minimalism, a simple empirical model with 2 input variables allowed high quality simulations of monthly discharge measured at 4000 m. Conclusion Glacier contribution at 4000 m is significant, in terms of quantity and hydrological regime regulation. Under actual climatic conditions, glacier contribution can be simulated using field observation of temperature and wind simulated by reanalysis. This result is of strong interest for future water resource simulations under climate warming scenarios.
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