Factors controlling the changes in surface water temperature in the Ebro River Basin

The Ebro River Basin, northeast Spain. The work analyzes the evolution of water temperature (Tw) in the Ebro River and its main tributaries, its annual cycle and its trends, as well as the effects of various natural and anthropogenic factors on them. Stations located downstream of nuclear power plants showed an anomalous increase in Tw not consistent with the river section where they are located, with higher values in the lower-flow months (August to December). The stations affected by the main reservoirs along the Ebro River showed a lower annual temperature range and the stations located in large irrigation systems showed a lower summer temperature compared to other stations with similar climatic conditions. Finally, there was a significant annual increase in Tw at all stations (mean ∆Tw=0.05 °C/year), except those located at the head of the tributaries. These trends were higher for the stations downstream of the Ascó nuclear power plant (∆Tw > 0.08 °C/year). Seasonally, the spring months showed the greatest changes, with higher increases at the stations downstream of Ascó (∆Tw ≥ 0.10 °C/year). The increase in air temperature associated with global warming and the decrease in flows associated with the increase in water consumption resulted in an increase in the temperature of the river. [Display omitted] •Evolution of water temperature in the Ebro River and its main tributaries.•Detection of anomalous temperature patterns and their changes over time.•Greatest anomalies at stations located downstream of thermal discharges from NPP.•Significant annual increase in water temperature at most stations, ∆Tw= 0.05 °C/year.•Greatest changes in spring months reaching ∆Tw ≥ 0.10 °C/year.