NATURAL AND HUMAN DRIVERS OF WATER-LEVEL FLUCTUATIONS IN US LAKES AND RESERVOIRS

Human water use and climate change (e.g., drought and flood frequency and duration) may pose serious threats to lake hydrologic integrity. Up to 59% of lakes in the conterminous US have exhibited water-level declines that exceeded least-disturbed conditions. But the interplay between human and natural factors in driving water-levels is not well known. Identifying regional variation in lake hydrology drivers can inform water management under changing environmental conditions. We developed a conceptual framework of natural (lake morphometry, watershed hydrology, and climate) and anthropogenic (dam height and land use) drivers of lake water-level decline and used path analysis to test and quantify the relationships. We compared models in the West (n = 357) and Midwest (n = 412) to examine how regional settings influence the magnitude and direction of human effects on lake water levels. In the West, human influences on vertical decline (31%) were greater than climate effects (14%) and associated with greater water-level decline. In the Midwest, climate effects (37%) were greater than human influences (9%), and human effects minimized water-level decline. These results suggest that large water-level declines in Western lakes result primarily from dam operation and water management and less from climate-related factors. Water levels in Midwestern lakes are more influenced by climate (drought), and management strategies stabilizes water levels. These regional differences provide insight into the role of regional management strategies on water-level declines.

Impact/Purpose

Natural lakes and constructed reservoirs provide important ecosystem services that include water sources for human activities (e.g., drinking water, recreation), habitat for wildlife, and buffers against adverse effects of drought and flooding. Disturbances such as land use intensification, water extraction and diversion, and changing climate conditions may significantly alter lake water-level regimes and lead to declining water levels. EPA’s Office of Water would like to understand how human interventions and management impact and interact with climate on declining water levels. We developed a conceptual framework of natural (lake morphometry, watershed hydrology, and climate) and anthropogenic (dam height and land use) drivers of lake water-level decline and used path analysis to test and quantify the relationships. Our results suggest that large water-level declines in Western lakes are primarily from dam operation and water management strategies and are less related to climate factors. In contrast, water levels in Midwestern lakes are more strongly influenced by climate (drought), and management strategies tend to promote full pools and stable water levels. These regional differences provide insight into the role of water management strategies on lake water levels under a changing climate.

Citation

Fergus, C., J. Renee Brooks, Phil Kaufmann, A. Pollard, R. Mitchell, A. Herlihy, Ryan A Hill, Steve Paulsen, P. Ringold, AND M. Weber. NATURAL AND HUMAN DRIVERS OF WATER-LEVEL FLUCTUATIONS IN US LAKES AND RESERVOIRS. ASLO 2021 Aquatic Sciences Meeting, NA, Virtual Meeting, June 22 - 27, 2021.