Warming of Near-Surface Summer Water Temperatures in Lakes of the Conterminous United States

Roger W Bachmann,Daniel E Canfield,Vincent Lecours,Sapna Sharma

doi:10.3390/w12123381

Roger W Bachmann, Daniel E Canfield + Show 2 more

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https://doi.org/10.3390/w12123381

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Journal: Water	Publication Date: Dec 2, 2020
Citations: 5	License type: CC BY 4.0

Affiliation: University of Florida, York University

Abstract

Because warming water temperatures have widespread consequences for freshwater communities, we were interested in estimating the patterns and rates of change of near-surface summer water temperatures in United States lakes. We developed multiple regression models to relate daily surface water temperatures in lakes of the conterminous United States to 8-day average air temperatures, latitude, elevation, and sampling month and year using data from 5723 lake samples in the months of June-September during the period 1981–2018. Our model explained 79% of the variation with a root-mean-square error of 1.69 °C. We predicted monthly average near-surface water temperatures for 1033 lakes for each year from 1981 through 2018. Lakes across the conterminous United States have been warming for the period 1981–2018 at an average heating rate of 0.32 °C per decade for the summer months (June–September). The average summer warming from 1981–2018 would be the equivalent of a lake decreasing 259 m in elevation or moving 233 km south. On the basis of national air temperatures starting in 1895, it was inferred that lake water temperatures are variable from year to year and have been steadily increasing since 1964, but that maximum temperatures in the 1930s were just as warm as those in 2008–2018.

Highlights

In recent decades, lakes have shown extensive responses to climate change including less seasonal winter ice cover [1,2], warmer surface water temperatures [3], modified mixing regimes [4], and decreases in water level and in surface water extent [5]
We found that 8-day average air temperatures, latitude, longitude, elevation, and month of sampling were important predictors of near-surface summer lake water temperatures for lakes distributed across the conterminous United States and southern Canada and developed an empirical model to predict summer near-surface water temperatures of unsampled lakes [16]
Piccolroaz et al [21] had cautioned about the use of air–water regression models when applied to air temperature ranges beyond the limits of the time series used in developing the equations

Summary

Introduction

Lakes have shown extensive responses to climate change including less seasonal winter ice cover [1,2], warmer surface water temperatures [3], modified mixing regimes [4], and decreases in water level and in surface water extent [5]. Because of the widespread importance of surface water temperatures to lake ecosystem functioning and ecosystem services, here we explore the patterns and trends in water temperatures across thousands of lakes distributed across the conterminous United States. Near-surface summer lake water temperatures are highly influenced by climate conditions, such as air temperatures, shortwave and longwave solar radiation, cloud cover, and wind speed [12,13,14,15]. Warmer lakes are found in regions with warmer air temperatures and higher solar radiation inputs [16]. Within the same region, smaller, shallower, and clearer lakes tend to be warmer [14,17,18]

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