Analysis of the Evolution of Climatic and Hydrological Variables in the Tagus River Basin, Spain

Gabriel Mezger,Marta González Del Tánago,Lucia De Stefano

doi:10.3390/w14050818

Gabriel Mezger, Marta González Del Tánago + Show 1 more

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https://doi.org/10.3390/w14050818

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Abstract

During the second half of the 20th century, several Spanish rivers experienced a decrease in the availability of water resources which coincided with an increase in human water demands. This situation is expected to be exacerbated by climate change. This study analyses the evolution of annual streamflow in 16 sub-basins of the Tagus River basin (Spain) during the 1950–2010 period and its relationship with selected variables. Our main objective is to characterize changes in in-stream flows and to identify what factors could have contributed to them. First, we used non-parametric tests to detect trends in the hydro-climatic series. Then, we analyzed changes in the runoff coefficient and applied regression-based techniques to detect anthropic drivers that could have influenced the observed trends. The analysis revealed a general decreasing trend in streamflow and an increasing trend in air temperature, while trends in precipitation are less clear. Residuals from regression models indicate that the evolution of several non-climatic factors is likely to have influenced the decline in streamflow. Our results suggest that the combination of the expansion of forested areas (a 60% increase from 1950 to 2010) and irrigated land (a 400% increase since 1950) could have played an important role in the reduction of streamflow in the Tagus basin.

Highlights

Many river basins in the Mediterranean region have experienced a decline in the availability of water resources since the 1980s [1]
Our study aims to characterize the historical evolution of streamflow in a large river basin in Spain—the Tagus—and explore the role that selected climatic and anthropic factors may have played in this evolution
In order to explore the influence of precipitation on the evolution of streamflow, we developed a regression model for each sub-basin in which the annual precipitation was set as the explanatory variable and annual streamflow as the dependent variable

Summary

Introduction

Many river basins in the Mediterranean region have experienced a decline in the availability of water resources since the 1980s [1]. Several studies have reported a generalized decrease in annual precipitation in this region during the second half of the last century [2,3] while average temperatures have risen [4,5]. These climatic trends have led to a reduction in streamflow in many river basins in the Mediterranean area over the past decades [1,6]. In addition to the reduction in the availability of water resources as a result of climatic changes, intensive water use has led to water stress in many regions across Europe [7]. At least 17% of the European Union (EU) territory experiences water scarcity and countries in the Mediterranean region are especially affected by this problem [8]. The expected rise in the demand for water in the near future [9] will undoubtedly contribute to exacerbating water stress in many European countries, especially in those with pre-existing water scarcity

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