Drinking-water warming risks due to temperature rise

Germany’s Rappbode reservoir, the largest drinking reservoir in Germany is at risk of warming up due to climate change which could present new water management challenges, an article in the Science Daily says.

Global temperature increase between 4 to 6 degrees by 2100 will also increase water temperature, creating new challenges to reservoir water management.

A group of researchers that Dr. Karsten Rinke leads looks at the possible implications and challenges this reservoir’s rising temperature brings. They observed that in the summer the reservoir’s water surface has already increased by about 4 degrees and has demonstrated that this trend will continue in the coming years.

The researchers based their projections on the three representative concentration pathways (RCPs): RCP 2.6, RCP 6, and RCP 8.5.

These RCPs shows various trajectories of GHG concentrations in the atmosphere adopted by the IPCC to describe and model different climate futures depending on whether emissions are abated or will continue to increase in the coming years and decades.

The latter, RCP 8.5, a worst-case scenario where emissions continue to rise throughout the 21^st century, will result in a water temperature increasing by .5 degrees every decade or about 4 degrees by 2100.

However, with drinking water which is usually drawn out from the bottom of the reservoir – at 50 meters deep, temperatures at that level could reach up to 8 degrees.

Consequences for this increased water temperatures would speed up “biological metabolic processes” which will increase oxygen consumption, but warmer water cannot absorb as much oxygen.

“Potential consequences include intensified dissolution of nutrients and dissolved metals from the sediment, algae growth and an increase in blue-green algae.”

According to the article, increased temperature will also increase the risk of contamination from the substances released from sediments and significant bacterial growth.

When this happens, water treatment efforts will likely increase and result in higher demands for treatment capacity. Operators are not helpless to deal with rising water temperatures though; they can use the procedure called, downstream discharge to cool down the surface or near-surface water.

Although, operators have solutions to deal with various water challenges, still when the air temperature increases to 6 degrees, it will be impossible to prevent the reservoir’s deep waters from heating up.

On top of this, other consequences of climate change like dry seasons, present another challenge to reservoir management.

Keeping deep waters in the reservoir cold will be in the best interest of drinking water suppliers and reservoir management operators. To do this will have to take ambitious climate policies that will limit global warming, the article says.