Slower snowmelt in a warmer world: 
Using observations and modeling to develop
a new theory of hydrologic change


Dr. Keith Musselman

NCAR



In many regions of the world, the melt of accumulated winter snowfall in forested and mountainous 
landscapes provides a critical water resource for streamflow and groundwater recharge. This seasonal 
resource is one of the fastest changing hydrologic features under global warming with broad impacts on 
economies, ecosystem function, and flood hazard. There is general consensus that projected warming will 
cause earlier snowmelt, but how snowmelt rates will respond to climate change is poorly known. I 
present snowpack observations from western North America illustrating that shallower snowpack melts 
earlier, and at lower rates, than deeper, later-lying snow-cover. The observations provide the context 
for a hypothesis of slower snowmelt in a warmer world. This hypothesis is tested using climate model 
simulations for both a control time period and re-run with a future climate scenario. The relative 
fraction of meltwater volume produced at high snowmelt rates is greatly reduced in a warmer climate. 
The reduction is caused by a contraction of the snowmelt season to a time of lower available energy, 
reducing by as much as 64% the snow-covered area exposed to energy sufficient to drive high snowmelt 
rates. These results have important implications on soil moisture deficits, vegetation stress, reduced 
basin water yield, and streamflow declines.