Using standardized precipitation and runoff indices for the identification of extraordinary drought events in Chile

Abstract

Chile has a wide variety of climates due to its geographical location, which covers over 4000 km from tropical regions in the north to the south Polar Regions. Drought of varying size and durations affecting different parts of the territory are commonly observed, including areas such as the arid Atacama Desert, the semi-arid central region, and the humid and very humid areas in the south. Despite the diversity of climates and weather conditions, the management of water resources in Chile is centralized. Thus, prior to making management decisions to cope with drought, the central water authority, must declare a drought as extraordinary. It is only after this declaration that the state can use public money to deliver aids, provide subsidies, allocate resources and implement other management tools. Recently the Standardized Precipitation Index (SPI) and the Standardized Runoff Index (SRI) were proposed as common indices to declare drought in the entire country. We studied the behavior of these indices throughout the territory for different durations (i.e., from 1 to 12 months), in order to identify the values that can be used to effectively declare extraordinary drought conditions in each region of the country. These indices were incorporated to the DGA’s regulation for declaring drought in 2012, and have become common and objective tools to deal with drought in Chile.