NATURAL AND ANTHROPOGENIC CONTROLS ON LAKE WATER-LEVEL DECLINE AND EVAPORATION-TO-INFLOW RATIO IN US LAKES

Human water use and climate change (e.g., drought and flood frequency and duration) pose serious threats to lake hydrologic integrity. 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 decisions 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 using the USEPA National Lakes Assessment 2007 and 2012 surveys. We compared models in the western (n = 357) and midwestern (n = 412) USA to examine how regional settings influence the magnitude and direction of water management effects on lake water levels. In the West, water management indicators had a greater total effect on vertical decline (standardized β = 0.38) than drought effects (standardized β = -0.15). In the Midwest, climate variables had greater total effects (drought standardized β = -0.20; mean annual temperature standardized β = 0.18) on vertical decline compared to water management effects (standardized β = -0.22) that were associated with more stable and full lake levels even during drought conditions. 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 act to stabilize water levels. Our findings highlight regional differences in the varied drivers of lake hydrology and provide insights into the role of water management strategies on lake water levels under a changing climate.

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 less so from direct climate effects.  In contrast, water levels in Midwestern lakes are more strongly related to climate (drought), and water management effects are weak but tend to promote full pools and stable water levels. Our findings highlight regional differences in the varied drivers of lake hydrology and provide insights into the role of water management strategies on lake water levels under a changing climate.

Citation

Fergus, E., J. Renee Brooks, Phil Kaufmann, A. Pollard, R. Mitchell, Ryan A Hill, Steve Paulsen, P. Ringold, AND M. Weber. NATURAL AND ANTHROPOGENIC CONTROLS ON LAKE WATER-LEVEL DECLINE AND EVAPORATION-TO-INFLOW RATIO IN US LAKES. Oregon Lakes Association, virtual, N/A, November 10, 2021.