Impact Assessment of Glacier Retreat on Catchment Water Resources in the Tropical Andes, Bolivia

Abstract:

Meltwater from glacier is one of the main water resources in the capital area of Bolivia. However, Andean tropical glaciers are rapidly shrinking during past some decades. We projected the response of glacier melt water, runoff and water temperature in reservoir to climate change. Objective area is Tuni reservoir catchment (90km²) with Condoriri, Tuni and HuaynaPotosi West glacier. This reservoir supplies approximately 30% of water consumption to urban area.

A glacier mass balance model was applied to Condoriri, Tuni and Huayna Potosi West glacier. Simulation period is 30 years from July, 2011. We produced four types of meteorological dataset for model input with observation data and output of general circulation model: one dataset assumes that current climate persists during 30 years and the others assume that temperature increase at the ratio of 0.02 to 0.04^oC/year. Furthermore, distributed runoff model and water quality model were also applied to understand the role of glacier meltwater in the Tuni reservoir catchment.

Projection shows that three glaciers decrease and reach equilibrium states of mass balance by the next three decades under current climate condition. Glacial area and meltwater are projected to be 40 to 60% and 60 to 80% of present by the end of 2030’s. HuaynaPotosi West glacier has higher uncertainty about the response of temperature rise than Tuni and Condoriri glacier. This is because the peak in altitudinal distribution of glacial area is higher than equilibrium line altitude for current climate condition.

 Projection of river discharge shows that meltwater from glacier dominates river discharge in early wet season, but meltwater from snow and rainfall dominates in mid wet season. Annual total inflow to reservoir decreases to about 40% of present condition without meltwater from glacier. Water temperature in reservoir is projected to be about 2^oC higher than present.