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

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.

Disclosing the effects of climate, land use, and water demand as drivers of hydrological trends in a Mediterranean river basin

“…Despite the differences in basin sizes, the decrease in mean daily flow observed over the past 60 years in the Onyar River largely corresponds with the widely documented decline in streamflow of various Iberian rivers (e.g. the Duero tributaries (Morán-Tejeda et al, 2010), the Tagus (Mezger et al, 2022), and the Ebro (Gallart et al, 2011), etc) This trend is consistent with changes observed in other basins throughout southern Europe (e.g. Croatia (Lutz et al, 2016), France (Folton et al, 2019), Italy (Darvini & Memmola, 2020), and across the entire Mediterranean basin (Masseroni et al, 2021)).…”

“…Other basins in the Iberian Peninsula have also experienced change-points in water runoff although timing can vary. For example, The Tagus River had a shift between 1979 and 1982 (Mezger et al, 2022), and runoff in the Noguera Pallaresa (Ebro basin) declined in the 1980s (Buendia et al, 2016). This shows that hydrological shifts are idiosyncratic, likely related to the specific hydrological events occurring in each basin, which in the Onyar River may be attributed to climate change and afforestation.…”

Precipitation and drought trends (1952–2021) in a key hydrological recharge area of the eastern Iberian Peninsula

“…Some hydrological studies have already pointed out this trend for the Tagus basin. Thus, Mezger et al (2022) observe a general trend toward decreased availability of water resources, which is made visible in the trend toward decreased flow, an aspect that they relate to the combination of several non climatic factors, among which the very marked role of increased irrigated land (of the order of 400%) should be highlighted. These results present a critical scenario of negative trends in river flows of several headwaters in the Iberian Peninsula at the same time, and these basins are not even anthropized (Martínez-Fernández et al, 2013).…”

Detecting, Analyzing, and Predicting Land Use/Land Cover (LULC) Changes in Arid Regions Using Landsat Images, CA-Markov Hybrid Model, and GIS Techniques

“…Human-induced LULC changes are driven mainly by the requirements of communities for food and economic development due to the rapidly increasing population growth globally [24][25][26][27][28]. These LULC shifts, however, have severe consequences for climate change, environmental conservation, environmental pollution, soil erosion, agricultural land production, biodiversity, and water resources [29][30][31][32][33][34][35][36][37]. In the investigation region, as arid land, the main driver of LULC changes is human activities due to population increase.…”