PNNL

The Science

Water management activities, such as irrigation withdrawals and dam operations, strongly influence the flow of water through a watershed.

Researchers from the U.S. Department of Energy's Pacific Northwest National Laboratory conducted the first regional modeling study to explore how these activities might modulate the effects of long-term changes in temperature and precipitation on regulated river flows. They found that close to half of the watersheds in the western United States could experience noticeable flow changes earlier in the century than they would in the absence of water management.

While results vary substantially across different watershed regions and seasons, the overall magnitude of change tends to be smaller in highly managed watersheds.

The Impact

This work is the first large-scale investigation of the "emergence of change" in highly regulated versus unregulated rivers—that is, it accounts for the influence of water management as well as for changing environmental conditions. Water management activities are generally thought to reduce flow variations, which was confirmed. However, the work revealed that water management can accelerate the emergence of these smaller changes.

The findings highlight significant regional and seasonal differences in how long-term Earth system changes will affect water availability. These results can be used to help understand and prepare for possible shifts in the timing and magnitude of future flows in the western United States. The research also highlights the need to account for human influences when constructing models of energy systems and other sectors that are strongly affected by changes in water availability.

Reference: T. Zhou, N. Voisin, G. Leng, M. Huang, and I. Kraucunas, "Sensitivity of Regulated Flow Regimes to Climate Change in the Western United States." Journal of Hydrometeorology 19, 3 (2018). [DOI: 10.1175/JHM-D-17-0095.1]