Natural and anthropogenic controls on lake water-level decline and evaporation-to-inflow ratio in the conterminous US
Citation:
Fergus, Carol, J. Renee Brooks, P. Kaufmann, A. Pollard, R. Mitchell, G. Geldhof, R. Hill, S. Paulsen, P. Ringold, AND M. Weber. Natural and anthropogenic controls on lake water-level decline and evaporation-to-inflow ratio in the conterminous US. LIMNOLOGY AND OCEANOGRAPHY. American Society of Limnology and Oceanography, Lawrence, KS, 67(7):1484-1501, (2022). https://doi.org/10.1002/lno.12097
Impact/Purpose:
Natural lakes and constructed reservoirs are important water resources of humans and provide essential ecosystem services such as drinking and irrigation water, 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 seeks to examine how human activities and water management impact and interact with climate on declining lake water levels. To disentangle the relative influence of natural and anthropogenic factors on lake water-level decline, we developed a conceptual framework of hypothesized natural (lake morphometry, watershed hydrology, and climate) and anthropogenic (dam height and land use) drivers of lake water levels and used structural equation models to test and quantify these relationships across the conterminous US. Our results demonstrate that in the West, large water-level declines in lakes were primarily related to dam and water management operations and less so from direct climate effects. In contrast, in the Midwest, lake water levels were more strongly related to climate (drought), and water management effects were weak but tended to promote full pools and stable water levels. Our findings highlight regional differences in natural and anthropogenic drivers of lake hydrology and provide insights into the role of water management strategies on lake water levels under a changing climate.
Description:
Lake hydrology is integral to lake ecological condition, but human-related water needs and changing climate conditions may alter hydrology beyond natural ranges. Separating natural and human effects can support lake management and assessment and requires a clear conceptual understanding of the multifaceted drivers of hydrologic variation across ecoregions and lake types. We constructed a conceptual model of morphometry, watershed hydrology, climate, and human water management drivers of lake water levels and evaporation-to-inflow ratio (E:I) across the conterminous US. Using a structural equation modeling framework, we tested our model using data from the US EPA National Lakes Assessment surveys. We applied the model to 1) a national subset of lakes with minimal water management infrastructure to establish natural background drivers of lake hydrology and 2) at ecoregional scales to explore how regional variation in water management and climate influence lake hydrology. Our model fit the national and ecoregional datasets (e.g., RMSEA < 0.08) and predicted lake E:I better than vertical water-level decline, showing that E:I is affected by watershed-level attributes and annual climate, whereas vertical decline may be related to predictors at finer spatial and temporal scales. For lakes with minimal water management presence, water-level decline was greatest in hydrologically-restricted lakes with drought conditions, and E:I was greatest in shallow lakes with little inflowing water. Anthropogenic effects varied by ecoregion and likely reflect differences in regional water management strategies. In the West, water management indicators were related to greater vertical decline, whereas in the Midwest, these indicators were related to more stable and full lake levels even during drought conditions. Our analyses indicated that water management infrastructure on lakes is widespread but their effects on lake hydrology are variable and may be adaptable to changing environmental conditions.
URLs/Downloads:
DOI: Natural and anthropogenic controls on lake water-level decline and evaporation-to-inflow ratio in the conterminous US