Drought conditions amplify river temperatures

In the wake of intensifying climate change, a recent study has shed light on the potentially dangerous consequences of increasing river temperatures due to droughts. 

The findings predict significant repercussions not just for aquatic organisms but also for human health and a variety of human activities that depend on rivers.

Focus of the study

River water temperature plays an important role in various physical, chemical, and biological processes. It is especially critical for fish, who lack the capability to self-regulate their body temperatures. 

Beyond its ecological importance, river temperature is also crucial for human health, industrial processes, domestic uses, and recreational activities.

Key mechanisms

In a collaborative review from the University of Birmingham, the University of Nottingham, and the Scottish Government’s Marine Directorate, experts have identified three main mechanisms that lead to increased river water temperatures during droughts:

Atmospheric energy inputs

This refers to the energy from the sun, especially intense shortwave radiation during arid, sweltering periods, identified as the leading cause of high river water temperatures.

Physical habitat influences

The shade provided by the riverside environment and the physical form of the river channel, which determines flow, are critical factors.

Contributions from different water sources

Interestingly, groundwater, which tends to be cooler, can actually help in reducing river temperatures during the summertime.

Compound effect of drought and warming

Drought conditions, which are marked by reduced water levels and slower flow velocities, make waters heat up faster. 

These conditions, when coupled with high atmospheric temperatures, form a lethal combination that can severely escalate river water temperatures. 

Droughts are anticipated to become both more intense and frequent due to climate change.

On the bright side, the researchers noted that certain cooling effects – such as groundwater influx, evaporation, and the shade provided by river channels – can act as temperature moderators in some situations.

Management interventions 

“Rising river water temperatures can have significant and often detrimental implications for aquatic life, impacting both individual species and entire ecosystems,” said study co-author David Hannah, professor of Hydrology and UNESCO Chair in Water Sciences at the University of Birmingham.

“Drought conditions often coincide with high atmospheric temperatures and such trends will become more intense and frequent with climate change – with major implications for river water temperatures due to the combination of intense solar radiation and lower (and slower) water flows.”

“However, certain management interventions such as riverside planting, and river restoration initiatives – including recreating natural channel forms and reconnecting groundwaters – could help to offset high thermal extremes during droughts if interventions are well targeted.”

Study implications 

The researchers noted that more holistic approaches to river restoration are required that consider how high river water temperature extremes can be offset while delivering other environmental and ecological benefits. 

They are calling for new scientific approaches to investigate how the three river temperature mechanisms they have identified may interact.

“Our work highlights critical future research questions that will help us to better model river water temperature dynamics during droughts – helping river managers to work out how thermal extremes could be better managed through mitigation and adaptation strategies,” said study lead author Dr. James White from the University of Birmingham.

The research is published in the journal Hydrological Processes.

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