"We show that the Pacific Northwest and northern California regions will experience new hydrological systems much earlier than other regions across the US," Maoyi Huang of Pacific Northwest National Laboratory told environmentalresearchweb. "Associated with these changes in what we call ‘hydrological regimes’ is a substantial increase in low and high extreme flow events. These projected changes will present greater challenges to water management in these regions as early as the 2030s."

Huang and colleagues used climate projections from 31 models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), under four RCP scenarios, in combination with the Variable Infiltration Capacity hydrologic model to assess the effect of climate change on hydrology.

"We demonstrated that almost half of the USA’s lower 48 states are likely to experience significant changes in those assumptions caused by ‘new normals’ in surface water systems by the end of the 21st century," said Huang.

A 1 °C increase in global mean temperature leads to 11% more lands experiencing runoff changes in summer and 17% more lands experiencing changes in winter, the team calculated.

In earlier projects, Huang and colleagues tried to understand the impacts of changes in streamflow on ecosystems and reservoir operations, particularly in the western US. After looking into the CMIP5-based dataset developed by the US Bureau of Reclamation, they realized its value and decided to expand the analysis to the whole US to learn how the projected changes will vary with time and space.

"We are now evaluating how water management (e.g. reservoir operation, irrigation) might change the new hydrological ‘regimes’ across the contiguous United States, and how might the energy system (i.e. hydro-power production) be influenced by such changes," said Huang. "The hydro-climatic scenarios are also serving as important boundary conditions for evaluating impact and vulnerability of local-scale ecosystems and infrastructure under future climate change."

Huang and colleagues reported their findings in Environmental Research Letters (ERL).

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