Water Management Impacts on Don River Annual Runoff under Modern Water Scarcity

Abstract

This study investigates the Don River’s behavior from 2014 to 2023, a period marked by exceptionally low annual water flow, with an annual runoff exceedance probability of 80% or greater. Runoff levels dropped considerably compared to the average observed between 1930 and 1980. This decline amounted to 24–29% in the upper basin, and a more substantial reduction of 42–52% occurred in the lower basin. The findings reveal that water scarcity is caused by a combination of climate change and human activities, with the magnitude of water management challenges being a particularly significant contributor. The strain on water management becomes even more significant during periods of low water availability. This is due to the ongoing but unmeasured effects of indirect factors such as changes in irrigation methods and urban expansion, which have been partially compensated for in recent times. We offer a quantitative evaluation of the runoff’s effects, taking into consideration groundwater and surface water withdrawals, water movements in and out of the basin, as well as extra evaporation from the Tsimlyansk Reservoir. Our research demonstrates that the cumulative impact of water management practices substantially contributes to periods of low water flow. Downstream of the Tsimlyansk HPP on the Don River, water flow has decreased by 23–26% compared to the average flow observed between 2014 and 2023. This decline is mainly attributed to the withdrawal and use of surface water, as well as an 11% loss due to evaporation from the Tsimlyansk Reservoir. This research evaluates groundwater extraction impact on runoff losses, differentiating between aquifers that are hydraulically connected to surface water and those that are not. While groundwater extraction and usage within the Don River’s basin contribute to a decrease in its annual water flow, this reduction is relatively minor, estimated at only 2 to 4%. Conversely, the groundwater contribution to river runoff bears a significantly heavier burden, representing 48% of its typical yearly volume.