From floods to fields: new horizons for reservoirs

Storing flood water in retention basins could provide much-needed water for agriculture in times of drought – without risking flood protection.

Drought is responsible for billions of Euros of damages per year in multiple sectors across Europe – and this goes beyond the drinking water supply. In agriculture, water shortages mean dying crops, in power generation, lower river and lake levels mean less hydropower, in commercial shipping, lower river levels also mean less cargo being transported. These consequences were on full display during 2018-2020 drought years in Europe, with ships nearly unable to traverse the Rhine and sweeping reductions in crop yields across Germany. In a warming world impacted by climate change, the severity and frequency of drought events—and with it, their consequences—are projected to increase.

At the same time, the increased severity and frequency of flood events provide an opportunity for potential synergistic effects: researchers at the CEDIM in a joint project with LUBW Baden-Württemberg are investigating the feasibility of flood reservoirs to provide much-needed water during times of drought without impacting their flood protection functions. In these potential operating concepts, reservoirs would store water until needed for drought mitigation instead of emptying immediately after flood events as per current operation rules. Flood protection levels would be maintained by ensuring that the reservoir was emptied before a flood occurred.

New results indicate that the additional water provided could have been substantial for preventing damage to agriculture in the vicinity of the reservoirs during the 2018-2020 drought years. Agricultural irrigation demand between 2017 and 2020 was estimated for areas around selected reservoirs in the southwest German state of Baden-Württemberg. Using this as a withdrawal schedule showed that many reservoirs were able to supply more than 70% of the needed irrigation water during these drought years, covering (on average) the needs of more than 100 hectares of farmland while maintaining the same level of flood protection.

Though significant research into the potential ecological consequences and challenges represented by forecasting is needed before implementing such a scheme, these results provide a promising proof-of-concept for ways to increase water and food security in a warming world.

Fig.: The potential demand fulfillment (i i.e., the ratio of total water provided to total demand, in %) of each of the 30 selected reservoirs is plotted against the reservoir's total estimated agricultural demand (in 1000 m3). Many of the reservoirs could have fulfilled a significant part (> 70% fulfillment) of the irrigation demand of their local region during the years 2017-2020. The less successful reservoirs (< 70% fulfillment) were restricted by the need to protect against frequent flood events, too high of an irrigation demand for the available reservoir capacity, and a lack of available water for storage.


Associated institute at KIT: Institute for Water and Environment – Hydrology
Authors: Sarah Ho, Uwe Ehret