 The continued retreat of glaciers will have a number of different quantitative effects . In areas that are heavily dependent on water runoff from glaciers that melt during the warmer summer months , a continuation of the current retreat will eventually deplete the glacial ice and substantially reduce or eliminate runoff . A reduction in runoff will affect the ability to irrigate crops and will reduce summer stream flows necessary to keep dams and reservoirs replenished . This situation is particularly acute for irrigation in South America , where numerous artificial lakes are filled almost exclusively by glacial melt . Central Asian countries have also been historically dependent on the seasonal glacier melt water for irrigation and drinking supplies . In Norway , the Alps , and the Pacific Northwest of North America , glacier runoff is important for hydropower . 
