IWRA Proceedings

Dire predictions of future water shortages tend to focus on areas of Africa and the Middle East, with scarce mention of the Americas. However, the prospect of adequate water resources to sustain existing and future demands for agricultural, industrial, and human needs is dependent upon demographics and climatic condition.  Changes in either population or climate can upset the delicate balance of water resource supply.  Peru faces an uncertain future for water supply due to a combination of both factors.
   
Precipitation in Peru is varied in space and time.  The Pacific coastal regions receive precipitation only rarely, but have a high percentage of the population.  To the east, the ranges of the Andes attract considerable precipitation during the normally wet summer months. Although tropical, the high altitudes result in accumulation of snow as glacial ice, sustaining runoff during the dry months of June through September.  River flow has provided water to the arid coast, as well as fostered development of agriculture and hydroelectric power generation in mountainous areas and intermontaine basins.

Short-term and long-term climate variations are affecting Peruvian water resources today, and may jeopardize long-term sustainability of water supply.  Although Peru has the greatest volume of glacial ice in the tropics, global warming has resulted in a 20-30% reduction of ice during the last three decades.  Unusually strong ENSO events (El Nino) have altered precipitation patterns for extended periods, resulting in locally severe flooding and decreased annual precipitation in normally wet areas.

To assess the present precipitation and runoff conditions, and to evaluate future sustainability issues, two river basins have been studied.  The Rio Santa in northwestern Peru drains portions of the Cordilleras Negra and Blanca, flowing through the Callejon de Huaylas to the Pacific. The Rio Vilcanota in southeastern Peru drains much of the area north of Lake Titicaca and is a major tributary of the Amazon.  Both rivers drain areas of extensive alpine glaciers, and both rivers have major hydroelectric plants in their lower reaches.  These similarities have resulted in good records of hydrologic conditions as well as long-term climate records from the glaciers. Efforts have been made in recent years to develop storage reservoirs high in the drainage basins in order to provide adequate flow for hydropower during prolonged dry periods.

If present trends continue, demand for water in both river basins will exceed supply in the near
future.  To ensure sustainability, additional storage capacity should be constructed within the basins. Increased development of ground water resources should also be encouraged to reduce impacts of short-term weather variation.