Streamflow seasonality in a snow-dwindling world.

Area of Science:

• Hydrology
• Climatology
• Environmental Science

Background:

• Climate warming is shifting cold regions from snow to rain, altering snowpack dynamics and impacting ecosystem services.
• Existing models suggest declining snowfall fraction leads to earlier snowmelt and streamflow, but this response is uncertain.

Purpose of the Study:

• To investigate the complex responses of streamflow timing to declining snowfall fraction across the Northern Hemisphere.
• To challenge the simplistic 'less snow equals earlier streamflow' heuristic.

Main Methods:

• Analyzed streamflow measurements from 3,049 snow-affected catchments across the Northern Hemisphere spanning 1950-2020.
• Examined the relationship between snowfall fraction and the timing of streamflow mass center.

Main Results:

• Declining snowfall fraction can lead to either advanced or delayed streamflow timing.
• The response of streamflow timing is modulated by the mean snowfall fraction, with snow-rich catchments showing earlier streamflow and less snowy catchments showing delayed streamflow.
• Interannual variability in streamflow timing and seasonal variation increase with decreasing snowfall fraction.

Conclusions:

• The relationship between snowfall fraction and streamflow timing is more complex than previously assumed.
• Findings indicate a nuanced evolution of seasonal streamflow regimes in response to decreasing snowpack.
• Revises the understanding of hydrological responses to climate change in snow-dominated regions.