The Missouri River basin, stretching from Montana to Missouri, is one of the largest river systems in the United States. Over the past century, the basin has experienced a significant 40% increase in average streamflow, with multiple years since 1990 seeing extremely high flows.
Streamflow is influenced by factors such as precipitation, temperature, humidity, atmospheric carbon dioxide (CO2), and land-use changes like deforestation for agriculture. Understanding these influences is crucial for predicting and preparing for hydrologic extremes, such as floods, which cost the U.S. billions of dollars annually.
Analyzing Streamflow Changes and the Impact of Natural Variability and Human Activities
A study published in AGU Advances by Dannenberg and colleagues analyzed these factors using land surface models and water budget simulations. Their goal was to determine the extent to which streamflow changes were driven by natural climate variability versus human activities.
Missouri River Basin Faces Increased Streamflow Amid Climate and Land-Use ChangesBy estimating past streamflow through discharge data and water budget models, they sought to understand the contribution of precipitation and evapotranspiration. Additionally, they divided the basin into six regions based on seasonal precipitation patterns to evaluate streamflow variations across different climate zones.
Between 1931 and 1960, the Missouri River basin’s mean annual water flow increased by over 900 cubic meters per second. The researchers attributed approximately 765 cubic meters per second of this rise to natural climate variability. Meanwhile, land-use changes, particularly the conversion of forests to croplands, contributed an additional 100 cubic meters per second. These findings indicate that while natural climate shifts were the primary driver of increased streamflow, human activities also played a measurable role.
Impact of Land-Use Changes and Future Risks of a Drier Climate State
The study found that land-use changes had a more significant effect during wet years, as cropland is less effective than forests in regulating extreme precipitation events. This effect was most noticeable in the lower basin, where agricultural expansion has been substantial.
Furthermore, rising atmospheric CO2 levels contributed to a 65 cubic meter per second increase in streamflow. These combined factors suggest that both human-driven environmental changes and natural climate variability have influenced the region’s hydrology.
The researchers warn that the recent increase in streamflow may be temporary, and a shift toward a drier climate state is possible. This drying trend could be worsened by human-induced global warming, leading to greater variability in water availability.
Such changes would have significant implications for agriculture, water management, and flood control in the Missouri River basin. Understanding these dynamics is critical for developing strategies to mitigate future hydrologic extremes and safeguard communities reliant on this vital water system.
