By David Tucker EBS CONTRIBUTOR
Recently, winter stormed back onto the
southwest Montana landscape. A March 24 storm left almost a foot of snow on the
slopes high above Big Sky, with a few inches dusting the meadows and canyons
closer to the Gallatin River. On the morning of March 25, our watershed’s
snowpack measured 116 percent of normal, according to the Natural Resource
Conservation Service.
That number bodes well for this year’s water
supply, as a deep mountain snowpack tends to guarantee the release of cold,
fresh water through the summer and early fall. When spring temps warm, snow
melts and runs off as surface flows in our creeks, streams and rivers. This
melt also seeps into the groundwater, recharging the aquifers that feed our
water supply. As of this moment, it appears 2020 will be a good year for water.
However, it has become increasingly hard to
use a deep winter snowpack to predict the behavior and availability of water
throughout spring and summer, due in large part to climate change-related
variability.
According to the Montana Climate Assessment
published in 2017, spring runoff is occurring earlier and faster than normal,
meaning water that previously remained in the watershed later in the season as
snow is now melting and running off downstream earlier. This limits late-season
river flows, and combined with warmer average temps, creates conditions harmful
to aquatic life while contributing to unwanted levels of algae like we saw in
2018. This could also lead to a lack of water for human use, a condition that
is exacerbated by growing demand from commercial and residential development.
This shift toward earlier runoff is related to
warming trends associated with human-caused climate change, and will likely
become more pronounced as time goes on. As the MCA suggests, Montana
temperatures are expected to rise by 4.5-6 degrees F by mid-century, and
warming is expected across all seasons.
While Montana is expected to warm, the state
is also expected to experience more precipitation, a trend that seems positive
for water supply. However, while scientists predict increased precipitation in
fall, winter and spring, the warmer temperatures mean less of this
precipitation will fall as snow.
Snow is critical to Montana’s water supply
because it is released slowly and consistently across the landscape. When water
falls as rain, it leaves the ecosystem faster, meaning less is available later
in the summer when precipitation amounts are lower. On top of this is the
expectation that summer precipitation is expected to decrease further, resulting
in less water making its way into our groundwater aquifers.
Adding to the water-retention challenges
associated with a warming climate are the human-altered landscapes that can
accelerate runoff. Sidewalks, driveways, roads and parking lots contribute to a
more rapid runoff, as water that hits these surfaces has no chance to seep into
the groundwater aquifers. Instead, the majority of this water, be it rain or snowmelt,
rushes straight to the river and downstream.
Mitigating this otherwise negative impact is
possible by way of stormwater management infrastructure like the conservation
garden planted at the Lone Peak High School parking lot, designed and funded by
the Gallatin River Task Force. The lot funnel’s water into a vegetated area.
Here, the flow is slowed and water can seep into the groundwater, and it is
better filtered before dumping into the Gallatin River.
While building this type of resiliency into Big
Sky’s water supply is a step in the right direction, and a necessary goal
regardless of climate change projections, more needs to be done to combat
warming trends and shifting precipitation patterns. If warming continues, there
simply won’t be enough water in the watershed for healthy ecosystem function or
human use.
David
Tucker is the communications manager for the Gallatin River Task Force.
