Examining the Effects of Climate Change on Managed Lowland Rivers

Water that is released from deep zones in stratified reservoirs can affect the natural thermal regimes of rivers. During the summer months, these water releases can substantially lower the water temperatures in rivers depending on the volume and temperature of these releases and the energy exchange with the overlying atmosphere. Previous studies have suggested the use of this cooling approach as a way to mitigate the effects of climate change. However, anticipated climate change conditions may weaken these cooling effects, especially in managed lowland rivers (MLRs). Here, we show that MLRs are vulnerable to water temperature increase, especially during the summer months subjected to a high emission greenhouse scenario. This vulnerability is exacerbated in low-flow conditions, especially at locations downstream of high-flow diversions. Whereas absorbed solar radiation will likely decrease in a future climate, the longwave and latent heat fluxes are major contributors to the increase in water temperature. Despite the warming effects of climate change on MLRs, our findings suggest that releasing hypolimnetic water from reservoirs during summer months can be a viable solution to mitigate the river temperature increase both upstream and downstream of water diversions.