The Colorado River and its tributaries supply water for hydropower, irrigation, and drinking water in several U.S. states and Mexico with much of the water coming from the snowpack that melts each spring. However, since 2000, water managers have been experiencing lower streamflow than predicted due to a lack of rainfall in the spring. The decreased rain leads to plants relying more on snowmelt for water, resulting in less water making its way into streams. The warmer, drier springs in recent years account for almost 70% of the discrepancy in predicted versus actual streamflow.
Researchers from the University of Washington have identified the lack of spring rainfall as the primary cause of the decrease in streamflow. Warmer, drier springs have led to reduced precipitation and increased evaporation from the soil, causing plants to draw more water from the snowpack. This trend started with the ‘Millennium drought’ in 2000, which has persisted to the present day. The researchers stress the importance of studying the entire snow season rather than just focusing on the snowpack’s depth to understand the cascading consequences of decreased springtime rain.
The research team, led by Daniel Hogan and Jessica Lundquist, investigated the phenomenon of decreasing streamflow in 26 headwater basins in the Upper Colorado River Basin. They analyzed streamflow and precipitation data dating back to 1964 to model plant water consumption in each basin. Their findings revealed that all basins showed reduced streamflow without spring rain, with lower elevation basins experiencing a more significant deficit due to earlier snowmelt, giving plants more time to consume the water.
The researchers’ findings highlight the importance of spring rain in influencing streamflow and plant water consumption in the Colorado River Basin. They are now exploring whether residual snow patches act as mini-reservoirs providing a constant source of water to nearby plants. As the Millennium drought persists, the accuracy of April water calculations will be increasingly affected by the lack of spring rainfall. The researchers emphasize the need to improve predictions of spring rain to enhance the accuracy of water availability estimates based on snowpack measurements in April.
This research was funded by the National Science Foundation, the Sublimation of Snow Project, and the Department of Energy Environmental System Science Division. By identifying the role of spring rain in impacting streamflow and plant water consumption, the researchers aim to enhance water management strategies in the Colorado River Basin. Their findings underscore the importance of understanding how climate change and precipitation patterns influence water availability in snow-fed river systems.