A recent study conducted by the University of Colorado Boulder reveals that snow in the mountain ranges of the Western U.S. and Canada is melting earlier, and there is an increase in rainfall instead of snow. This change in precipitation patterns is causing a reduction in the snowpack, which can have significant implications for various sectors. Agriculture, wildfire risk, and municipal water supplies may be affected during the summer months due to the diminished snowpack. This study highlights the potential consequences of a leaner snowpack and emphasizes the need for further understanding and proactive measures to mitigate the impacts on these important aspects of the region’s ecosystems and communities.
The study, published in the journal Nature Communications Earth & Environment, focuses on the changes in snowpack water storage across Western North America over a span of more than 60 years. The researchers discovered a notable decline in snowpack water storage in over 25% of the Mountain West region between 1950 and 2013. This decline can be attributed, at least in part, to increased melting of snow during the winter and spring seasons, which is blurring the traditional seasonal boundary of snow accumulation and melt. These findings provide valuable insights into the long-term trends of snowpack water storage and its implications for water resources in the region.
According to Kate Hale, the lead author of the study and a geography graduate, the research findings indicate that snow melt is now happening closer in time to when the snowfall occurred. This shift in timing means that water availability is shifting towards earlier in the spring, leading to reduced snow melt and less water availability later in the summer. This trend suggests that there may be water scarcity issues later in the year, potentially impacting various sectors that rely on water resources.
Timing is everything
Indeed, the Western U.S. and Canada heavily rely on snow as a crucial water source. Mountain ranges like the Rocky Mountains and Sierra Nevadas act as natural reservoirs, accumulating snow during the winter months. The gradual melting of this snowpack during spring and summer ensures a steady supply of water during the high-demand seasons. However, the changing patterns of earlier snow melt and increased rainfall instead of snow are affecting the traditional functioning of these “water towers.” As a result, the region may experience challenges in meeting water demands for agriculture, municipal water supplies, and mitigating wildfire risks in the future.
The snow water equivalent (SWE) is an important metric used by water managers to assess the amount of water that will be generated when a particular volume of snow melts. This measurement helps them predict and plan for water resources throughout the year. Traditionally, April 1 is a significant date for this assessment, as it marks a crucial point in the snow accumulation and melting process. By measuring SWE, water managers can make informed decisions about water allocation, storage, and distribution, considering factors such as agricultural needs, water supplies for communities, and environmental requirements. However, with the changing snowpack dynamics and earlier snow melt, the accuracy and reliability of these predictions may be affected, posing challenges for water resource planning and management.
But that April 1 snapshot is exactly that: one moment in time. It doesn’t reveal if that snow slowly accumulated over the past six months, if it all fell in one giant heap on March 31, or if it was already melting.
Noah Molotch, an associate professor of geography and a fellow at the Institute of Arctic and Alpine Research (INSTAAR) at CU Boulder, emphasizes that snow plays a unique role in delaying the timing of water input to watersheds. Simply looking at the snapshot of snow water equivalent (SWE) on a specific date doesn’t provide information about how long that snow has been present. The duration of snow cover is an important factor that affects the hydrological processes in a region. Understanding the temporal aspects of snow accumulation and melt is crucial for accurately assessing water availability and managing water resources in watersheds.
Kate Hale developed a new measurement called the Snow Storage Index (SSI) by combining data from two publicly available sources. The SSI takes into account not only the amount of snowfall and snowmelt but also the timing of these events before and after April 1. Unlike the Snow Water Equivalent (SWE), which provides a snapshot of snowpack at a specific moment, the SSI captures the temporal aspect of snow accumulation and melt. It represents a “video” of the winter season, showing the duration between when precipitation falls as rain or snow and when it becomes available as surface water in a particular area. By incorporating both timing and quantity, the SSI provides a more comprehensive understanding of the water storage dynamics in snow-covered regions.
Noah Molotch highlights that the Snow Storage Index (SSI) provides valuable insights into snow water storage dynamics by considering not only the quantity of snow at a specific moment but also the duration of its presence on the ground. This broader perspective allows researchers and water managers to assess the length of time that snow serves as a storage reservoir before melting and contributing to water resources. By incorporating duration, the SSI provides a more comprehensive understanding of the overall water storage capacity of snowpack in a given area.
This allowed the researchers to analyze how well each mountainous region of the West has acted as a water tower over the past 60 years and discover that their performance has been declining across the board.
Managing water now and for the future
The SSI provides insights into the specific characteristics of snow water storage in different regions. A high SSI value close to 1.0 indicates that snowfall is highly seasonal, with snow accumulating during fall and winter and remaining on the ground for a longer duration before melting in the spring and summer. This pattern is observed in places like the Cascades, where snow is stored for up to six months before gradual melting occurs.
On the other hand, regions with a lower SSI, such as the Colorado Rocky Mountains, experience a different snow water storage pattern. In these areas, snow accumulation and melting occur throughout the colder half of the year, resulting in a more continuous snowmelt process. The SSI values between 0 and 0.5 in Colorado’s Rocky Mountains reflect this dynamic snowpack behavior.
By considering the SSI, researchers can better understand the timing and duration of snow water storage in different regions, which is crucial for assessing water availability and managing water resources effectively.
The Rockies and the Front Range are used to snow falling and melting during winter and spring, so they might be able to handle less snowpack water storage caused by global warming. But mountain regions near the West Coast, which rely on melting snow for water in spring and summer, might face difficulties when the snow melts earlier and there’s less water available later in the summer.
The researchers hope that this new measurement can serve as a tool for scientists and water resource managers to make better predictions and, when necessary, plan ahead for less.
Around 50 years ago, the Western United States experienced a period of constructing dams, which greatly increased access to water for cities and agriculture. However, as the snowpack and water storage in the mountains decline, the reservoirs that depend on them may also see reduced water levels.
According to Molotch, the visible erosion and disappearance of the snowpack will pose challenges in managing the infrastructure that has supported the growth and prosperity of the Western United States over the past century. This suggests that there will be a need for adaptation and new approaches to address the changing water availability in the region.
Additional authors on this publication include: Keith Jennings, Lynker, Boulder, Colorado; Keith Musselman, Department of Geography and the Institute of Arctic and Alpine Research (INSTAAR), CU Boulder; and Ben Livneh, Cooperative Institute for Research in Environmental Sciences (CIRES) and the Department of Civil, Environmental, and Architectural Engineering, CU Boulder.
