Dry getting drier – The future of transnational river basins in Iberia

Selma B Guerreiro,Stephen Birkinshaw,Chris Kilsby,Hayley J Fowler,Elizabeth Lewis

doi:10.1016/j.ejrh.2017.05.009

Selma B Guerreiro, Stephen Birkinshaw + Show 3 more

Open Access

https://doi.org/10.1016/j.ejrh.2017.05.009

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Abstract

Study regionMain international rivers of Iberia (SW Europe): Douro, Tagus and Guadiana. Study focusIberia has long suffered from water scarcity which will worsen with projected reductions in rainfall and increases in temperature. Nonetheless, there has been almost no research concerning the future discharges of these rivers. We examine an ensemble of climate model projections from CMIP5 RCP 8.5 and use two downscaling methods to produce a range of changes in discharge using a physically-based, spatially-distributed hydrological model (SHETRAN) for historical (1961–1990) and future (2040–2070) periods. New hydrological insights for the regionThere is uncertainty in the sign of change in high (winter) discharges but most model runs show decreases in monthly, seasonal and annual discharges for all basins; especially for medium and low discharges, with all but one run showing future decreases. The magnitude of these decreases varies significantly for different CMIP5 ensemble members. However, autumn shows the biggest decreases (reaching −61% for the Douro, −71% in the Tagus, and −92% for the Guadiana) and the reductions are consistently larger for the Guadiana. This is the first study to explore a wide range of possible futures for these international basins. We show that, despite uncertainties in model projections, there is common behavior with reductions in mean and especially in low discharges which will have important implications for water resources, populations, ecology and agriculture.

Highlights

Portugal and Spain share five river basins which cover 40% of the Iberia peninsula
The circulation-pattern-based method produced smaller reductions in flows (21% for Guadiana and 20% for Tagus) than the bias correction method (26% and 49%)
SHETRAN is a physically-based distributed hydrological model that can be visualized as a set of vertical columns, with each column divided into finite-difference cells

Summary

Introduction

Portugal and Spain share five river basins which cover 40% of the Iberia peninsula. Under natural conditions around 70% of the total outlet flow of the three main international Iberian rivers, the Douro, the Tagus and the Guadiana, has its origin in Spain (INAG, 2001). The first water treaties between Portugal and Spain date back to the 19th century and several treaties were later signed in the 1920s and 1960s. The latest, from 1998, is the Albufeira Convention. This convention seeks to balance environmental protection with sustainable use of water resources within the framework of International and EU Law (UN, 2013). In 2008 a seasonal flow regime for the Douro, Tagus and Guadiana was defined (as a revision of the convention), which includes minimum flows for different times of the year

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