Reduced spring flooding a result of climate change – may be counteracted through water regulation

In Sweden and other areas of the world with snow cover part of the year, the regulation of rivers has altered the flow regimes of springtime floods to at least as great an extent as coming climate change will alter them. Scientists are now suggesting that water regulation could be used in climate adaptation as a way to recreate the natural variation in water flow regimes.

As Earth’s climate changes, powerful floods during spring will become increasingly rare. The snowy season will become shorter, the spring thaw will start earlier, and the springtime floods will become more moderate with the flow of water more evenly distributed throughout the year. This will affect the natural environments and ecosystems that depend upon periodic flooding.

Roughly the same impact

Most Swedish rivers are regulated. This allows melt water from snowmelt to be stored in reservoirs, to be used in the production of hydroelectric power at other times of the year.

Now, a new scientific study indicates that one fifth of the annual water discharge is reallocated by hydroelectric power production to other periods of the year. Just as much impact is expected from climate change caused by global warming.

On the national scale for Sweden, hydroelectric power production evens out the flow regimes from the spring floods in the same manner as will be brought about by continued climate change. However, in some areas downstream from major water reservoirs, the impact of water regulation is much greater than the changes in water flow regimes caused by climate change.

“This means that much of the country has already been even more greatly affected by the flood dynamic than they will be in the future climate and for the large landmass we have already impacted the conditions in the same manner as climate change,” explains Berit Arheimer, a hydrology researcher at the Swedish Meteorological and Hydrological Institute (SMHI) and leader of the team that carried out the study.

Springtime flooding in northern Sweden
Springtime flooding in Överkalix in northern part of Sweden in May of 2017. Foto Emil Söderström, SMHI

The ability to recreate natural conditions

“On the other hand, the regulations could be used to counteract the effects of climate change and to recreate a natural springtime flood in an artificial manner, by releasing water from the reservoirs at special points in time. Doing so would preserve the biodiversity of the lower parts of the major rivers,” elaborates Berit Arheimer.

Relevant in areas with snow cover

The results of the comparison between the impacts of springtime flooding from hydroelectric power production compared to that resulting from climate change do not merely apply to Sweden. They are valid in all parts of the world that experience snow cover for some part of the year and which regulate their waterways for the purpose of energy production. Therefore, in order to carry out credible global analyses of climate impact, water regulations must be included in calculations of the water balance.

Access to open data is crucial

Currently, it is difficult to get hold of information about and receive access to open data related to reservoirs and regulatory levels. This data is necessary in order to better understand how the combined impact of both factors changes water flow regimes on a large scale.

The regulatory levels of all rivers and lakes across Sweden are available in high resolution on the SMHI Vattenwebb (Waterweb). Data of estimated river flow for both natural and regulated conditions may be freely downloaded from the site.

The study is presented in a scientific article in Nature Communications, under the title 'Regulation of snow-fed rivers affects flow regimes more than climate change'.