Melting Glacial Ice
Water supplies can also be affected by warmer winter temperatures that cause a decrease in the volume of snowpack. The result is diminished water resources during the summer months. This water supply is particularly important at the midlatitudes and in mountainous regions that depend upon glacial runoff to replenish river systems and groundwater supplies. Consequently, these areas will become increasingly susceptible to water shortages with time, because increased temperatures will initially result in a rapid rise in glacial meltwater during the summer months, followed by a decrease in melt as the size of glaciers continue to shrink. This reduction in glacial runoff water is projected to affect approximately one-sixth of the world's population (IPCC 2007).
A reduction of glacial runoff has already been observed in the Andes, whereby the usual trend of glacial replenishment during winter months has been insufficient. This is due to increased temperatures, which have caused the glaciers to retreat. It is likely that Andean communities such as El Alto in Bolivia have already observed a reduction in glacial runoff due to the scattered distribution of smaller sized glaciers, which further reduces the potential for runoff. In these areas, approximately one-third of the drinking water is dependent upon these supplies, and the recurrent trend of increased melt with diminished replenishment provides a dismal projection for water reserves if this same pattern continues (Goudie 2006).