Temporal variations of rainfall and flows in the Maipo River Basin, central Chile, and the influence of glacier melting on water yield (1963-2006)

Abstract

In this paper, precipitation and runoff trends over the past 40 years are inferred for two sub-basins of the Maipti River: El Colorado (1 710 km(2)) and the Alto del Maipo (3521.52 km(2)). The two sub-basins are located in the metropolitan region of Chile and have markedly snowy regimes. Five rain gauge stations with monthly and annual records (mm) were analyzed for the period 1963-2006. After completing the missing information for each station, mean areal precipitation was calculated using the Thiessen Polygons Method. Monthly and annual mean flow data were extracted from two flow gauging stations. The analysis of temporal behavior for rainfall and runoff variables was performed by adjusting the Type-1 Gumbel distribution function and calculating moving averages and the rainfall/runoff coefficient (existing ratio of rainfall to surface runoff; PP/E, abbreviation in Spanish). Thus, it was possible to determine that, over the last 40 years, the Maipo River basin showed increased winter rainfall, decreased summer and autumn rainfall and increased runoff during summer periods. Therefore, it can be inferred that the increase in this runoff is influenced by glacier melting.