Abstract
ABSTRACTWater scarcity is a critical issue in Iberia but few studies have investigated future drought over the region. The few that do are continental or global studies and do not report the range of possible future projections. In this paper, historical drought and future projections of drought were examined, using observed and downscaled rainfall data from climate models, for the main Iberian international basins (Douro, Tagus and Guadiana). Two drought indices were used, the standardized precipitation index (SPI) and the drought severity index (DSI). However, problems were found in the distribution fitting required for the calculation of SPI which render this index inadequate for assessing droughts in Iberia. The skill of CMIP5 climate models in representing historical drought for the Douro, Tagus and Guadiana is very variable with some not showing enough persistence of dry conditions, and others simulating droughts that are too long and too severe. Nevertheless, the observed range of drought conditions for these basins was encompassed by the ensemble members. Furthermore, we found no relationship between performance in simulating mean large‐scale circulation and model ability to reproduce the historical drought characteristics for the region. All models project an intensification of drought conditions for the three basins. However, some only project small increases, while most project extreme multi‐year droughts by the end of the century. We found that climate model future projections are neither related to their performance in simulating historical drought nor to their large‐scale circulation patterns. This result emphasises the need for climate change impact studies to take into account the whole range of climate model projections in order to provide the best information for robust adaptation. Choosing one or a subset of climate models based on historical performance would not lead to a credible and justified reduction in uncertainty.
Highlights
Water scarcity is a critical issue in Iberia due to the region’s large interannual variability of rainfall, combined with an uneven spatial and seasonal distribution (Trigo and DaCamara, 2000; Goodess and Jones, 2002; Rodrigo and Trigo, 2007; González-Hidalgo et al, 2010; Guerreiro et al, 2014)
We found that all models underestimate the frequency of severe drought in the Douro
Model 15 never reaches a drought severity index (DSI)-12 of 50% for the Guadiana, and only does so once for the Douro and the Tagus showing a lack of persistence of dry conditions
Summary
Water scarcity is a critical issue in Iberia due to the region’s large interannual variability of rainfall, combined with an uneven spatial and seasonal distribution (Trigo and DaCamara, 2000; Goodess and Jones, 2002; Rodrigo and Trigo, 2007; González-Hidalgo et al, 2010; Guerreiro et al, 2014). The main international Iberian rivers, the Douro, the Tagus and the Guadiana (see Figure 1), are vital water resources in Portugal and Spain, covering around 40% of the Iberian Peninsula. Their flows are regulated by an international convention between the two countries (Almeida et al, 2009). Spatial patterns of drought in Iberia vary according to the time-scale studied (Vicente-Serrano, 2006b) and only the most extreme droughts affect the entire peninsula (Vicente-Serrano, 2006a). The worst droughts in Spain were during 1941/1945, 1979/1983, and 1990/1995 and affected most of the country, with reductions in rainfall from 23 to 30% resulting in runoff reductions of
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