Abstract
Abstract. In this study we analyzed the spatiotemporal variability of streamflow droughts in the Iberian Peninsula from 1945 to 2005. Streamflow series belonging to 187 homogeneously distributed gauging stations across the study area were used to develop a standardized streamflow index (SSI), which facilitated comparison among regimes and basins, regardless of streamflow magnitudes. A principal component analysis was performed to identify homogeneous hydrological regions having common features based on the temporal evolution of streamflows. Identification of drought events was carried out using a threshold level approach. We assessed the duration and magnitude of drought episodes and the changes that occurred between two contrasting periods for each hydrological region. The results showed a trend toward increased drought severity in the majority of regions. Drought duration, magnitude and spatial coverage were found to depend mainly on climatic conditions and the water storage strategies in each basin. In some basins these strategies have altered river regimes, and in others created a high level of dependence on storage and water transfer rates.
Highlights
Among natural hazards, drought is one of the most damaging and affects more people than any other (Obasi, 1994), causing negative ecological, economic, agricultural, social and political impacts
The boxplots indicate the range of values of the impoundment ratio, elevation, slope and annual discharge for the subbasins belonging to each principal component (PC)
We considered the first ten PCs, which together explained 60 % of the total variance; this was considered to represent a reasonable portion of the very high variability of the streamflow behavior, since the variability of Iberian monthly precipitation was summarized into 6 components (70 % of the variance, Vicente-Serrano et al, 2006b)
Summary
Drought is one of the most damaging and affects more people than any other (Obasi, 1994), causing negative ecological, economic, agricultural, social and political impacts. Many European countries have experienced problems arising from droughts during recent decades, including restrictions on water usage for urban consumption and leisure, reductions in electricity supply (European Environmental Agency; EEA, 2001), crop production losses and increased forest fires. Drought has been defined as the naturally occurring phenomenon that exists when precipitation has been significantly below normal recorded levels, causing serious hydrological imbalances that adversely affect production systems (UN Secretariat General, 1994). Contrary to other climaterelated hazards such as floods, which are generally restricted to small regions and have well-defined temporal intervals, droughts are difficult to quantify and pinpoint in time and space, as they develop slowly and last for long periods (Vicente-Serrano, 2006a). Droughts have been classified into four categories (meteorological, agricultural, hydrological and socioeconomic) based on the system affected and the time scale in which the drought impacts become evident (Wilhite and Glantz, 1985)
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