Figure: Snowy mountain stream. Image credit: NASA.
As the snow goes, so does the [summer] flow
The motivation – In seasonally snow-covered regions, snowmelt is an important component of streamflow. The annual cycle of snow accumulation and melt allows for natural water storage and carry-over, with snowmelt recharging groundwater and providing ecosystem-sustaining streamflow during the warmer, drier summer months. The normal, annual recurring period of low streamflow during summer is often referred to as the summer “low flow” period. Climate change is expected to have large impacts on snowmelt hydrology. However, the relative importance of temperature versus precipitation on low flows is unclear and, thus, so is our understanding of how the summer water quantity in these seasonally snow-covered regions may change in the future.
The discovery – Led by an Earth Sciences Ph.D. student, Jennifer Dierauer, researchers in the Allen group developed a robust low flow regime classification methodology and completed an empirical analysis of observed streamflow records for 63 mountain catchments in western North America. The study shows that, compared to annual streamflow, summer streamflow is up to two times more sensitive to temperature – particularly, winter temperatures above 0°C. Thus, in these seasonally snow-covered catchments, warm winters lead to longer, more severe summer low flow periods and shorter, less severe winter low flow periods.
Its significance – Water management practices are often dependent on the natural water storage provided by seasonal snowpack. As winters become warmer, snowpack storage will likely decrease. As the snow goes, so does the summer flow, and what we consider to be a summer streamflow “drought” now, may become the norm in the future.
Read the paper – “Climate Controls on Runoff and Low Flows in Mountain Catchments of Western North America” by Dierauer, JR; Whitfield, PH; Allen, DM. Water Resources Research 54(10):7495-7510 (2018). DOI: 10.1029/2018WR023087.
Website article compiled by Jacqueline Watson with Theresa Kitos