Global lake responses to climate change
Article
Accepted Version
Woolway, R. I. ORCID: https://orcid.org/0000-0003-0498-7968,
Kraemer, B. M. ORCID: https://orcid.org/0000-0002-3390-
9005, Lenters, J. D., Merchant, C. J. ORCID:
https://orcid.org/0000-0003-4687-9850, O’Reilly, C. M. ORCID:
https://orcid.org/0000-0001-9685-3697 and Sharma, S. (2020)
Global lake responses to climate change. Nature Reviews
Earth & Environment, 1. pp. 388-403. ISSN 2662-138X doi:
https://doi.org/10.1038/s43017-020-0067-5 Available at
https://centaur.reading.ac.uk/91787/
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Global lake responses to climate change
1
2
R. Iestyn Woolway
1,2
†
, Benjamin M. Kraemer
3,11
, John D. Lenters
4,5,6,11
, Christopher J.
3
Merchant
7,8,11
, Catherine M. O’Reilly
9,11
, Sapna Sharma
10,11
4
5
1
Centre for Freshwater and Environmental Studies, Dundalk Institute of Technology,
6
Dundalk, Ireland
7
2
European Space Agency Climate Office, ECSAT, Harwell Campus, Didcot, Oxfordshire,
8
UK
9
3
Ecosystem Research Department, IGB Leibniz Institute of Freshwater Ecology and
10
Inland Fisheries, Berlin, Germany
11
4
Bureau of Water Quality, Wisconsin Department of Natural Resources, UW-Trout Lake
12
Research Station, Boulder Junction, WI, USA
13
5
Center for Limnology, University of Wisconsin-Madison, Madison, WI, USA
14
6
Great Lakes Research Center, Michigan Technological University, Houghton, MI, USA
15
7
Department of Meteorology, University of Reading, Reading, UK
16
8
National Centre for Earth Observation, University of Reading, Reading, UK
17
9
Department of Geography, Geology, and the Environment, Illinois State University,
18
Normal, IL, USA
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10
Department of Biology, York University, Toronto, Ontario, Canada
20
11
These authors are listed in alphabetical order because contributions were similar
21
22
†
email: riwoolway@gmail.com
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Key points
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• Due to climate change, lakes are experiencing less ice cover, with over 100,000 lakes at
26
risk of having ice-free winters if air temperatures increase by 4°C. Ice duration has become
27
28 days shorter on average over the past 150 years for Northern Hemisphere lakes, with
28
higher rates of change in recent decades.
29
• Lake surface water temperatures have increased worldwide at a global average rate of 0.34
30
°C decade
-1
, which is similar to or in excess of air temperature trends.
31
• Global annual mean lake evaporation rates are forecast to increase 16% by 2100, with
32
regional variations dependent on factors such as ice cover, stratification, wind speed and
33
solar radiation.
34
• Global lake water storage is sensitive to climate change, but with substantial regional
35
variability, and the magnitude of future changes in lake water storage remains uncertain.
36
• Decreases in winter ice cover and increasing lake surface water temperatures have led to
37
mixing regime alterations that typically have resulted in less frequent mixing of lakes.
38
• Ecological consequences of these physical changes vary widely depending upon location,
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lake depth and area, mixing regime, and trophic status.
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2
Abstract
43
Climate change is one of the most severe threats to global lake ecosystems. Lake surface
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conditions, such as ice cover, surface temperature, evaporation and water level respond
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dramatically to climate change, as observed in recent decades. In this Review, we discuss physical
46
lake variables and their responses to climate change. Decreases in winter ice cover and increases
47
in lake surface temperature modify lake mixing regimes and accelerate lake evaporation. Where
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not balanced by increased mean precipitation or inflow, higher evaporation rates will favour a
49
decrease in lake level and surface water extent. Together with increases in extreme precipitation
50
events, these lake responses to climate change will impact lake ecosystems, changing water
51
quantity and quality, food provisioning, recreational opportunities, and transportation. Future
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research opportunities, including enhanced observation of lake variables from space (particularly
53
for small water bodies), improved in-situ lake monitoring, and the development of advanced
54
modelling techniques to predict lake processes, will improve our global understanding of lake
55
responses to a changing climate.
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[H1] Introduction
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Lakes are a critical natural resource that are sensitive to changes in climate. There are more than
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100 million lakes globally
1
, holding 87% of Earth’s liquid surface freshwater
2
. Lakes support a
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global heritage of biodiversity
3
and provide key ecosystem services
4
; as such, they are included in
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the United Nations’ Sustainable Development Goals committed to water resources (Goal #6) and
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the impacts of climate change (Goal #13)
5
. Lakes are also key indicators of local and regional
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watershed changes, making lakes useful for detecting Earth’s response to climate change
6
.
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Specifically, variables such as lake surface temperature, water level and extent, ice cover, and lake
65
colour are recognised by the Global Climate Observing System (GCOS) as Essential Climate
66
Variables (ECVs) because they contribute critically to the characterization of Earth’s climate. The
67
scientific value of lake research makes it an essential component of the United Nations Framework
68
Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change
69
(IPCC).
70
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Lakes are already responding rapidly to climate change. Some of the most pervasive and
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concerning physical consequences of climate change on lakes are the loss of ice cover
7
, changes in
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evaporation and water budgets
8, 9
, warming surface water temperature
10
, and alterations in mixing
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regimes
11
. These lake variables interact with one another (Fig. 1), complicating our ability to
75
predict lake physical responses to climatic variations. For example, changes in ice cover and water
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temperature modify (and are influenced by) evaporation rates
9
, which can subsequently alter lake
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levels and surface water extent
12
. In the absence of precipitation changes, one of the effects of
78
reduced ice cover, higher surface water temperatures, and increased lake evaporation rates could
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be reductions in lake level and extent. However, land surface runoff and direct precipitation to the
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lake also affect lake level and extent, which are subject to climatic variations across the lake
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catchment, reinforcing or even offsetting the effects mediated by evaporation. Such sensitive
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balances between climatically driven factors lead to spatially variable outcomes for lake-climate
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interactions that require further elucidation to understand and predict.
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85
3
In this Review, we summarize the responses of key physical lake variables and processes to global
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climate change, including ice cover, surface water temperature, evaporation, water levels, and
87
mixing regimes, and outline their ecological consequences (Fig. 1). We also identify research needs
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for improving our global understanding of lake responses to climatic variability and change,
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including enhancing satellite observations and in-situ technology for monitoring both small lakes
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(which dominate the global lake distribution) and large lakes with high spatial heterogeneity,
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developing global-scale modelling techniques to better predict lake responses under climate
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change, and establishing collaborations between limnologists and remote sensing scientists.
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[H1] Decreasing lake ice
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Lake ice phenology - the timing of ice freeze and breakup - is a sensitive indicator of climate
13, 14
.
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Lake ice formation is dictated by the surface energy balance and mediated by air temperature, lake
97
morphology, wind-induced mixing, and other meteorological, morphometric, and hydrologic
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influences
15
. For example, heat loss from the lake surface during the ice-formation process occurs
99
primarily through outgoing longwave radiation and sensible and latent heat flux
16
. As such, initial
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ice formation often occurs at night under cold, calm, clear-sky conditions. However, strong cooling
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and deep mixing is often required to “prime” the lake prior to initial ice formation at the surface,
102
typically through cold, dry, wind events that lead to strong sensible and evaporative heat loss
17
.
103
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Lake depth also modulates ice formation, thickness, and spatial coverage, as deeper lakes take
105
longer to cool in autumn
7, 15, 18
. Air temperatures in autumn need to be below 0°C for a longer
106
period of time before deeper lakes freeze
19
, and deep lakes are more sensitive to experiencing
107
intermittent winter ice cover (that is, not freezing every winter)
7
. Larger lakes with a longer fetch
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[G] tend to also freeze later, as they are more sensitive to increased wind action breaking up the
109
initial skim of ice on the lake surface
20, 21
. Thus, under scenarios of climate warming, deeper lakes
110
with larger fetch are expected to be more susceptible to losing ice cover than shallower lakes within
111
the same region
7, 21
.
112
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The timing of lake ice breakup is generally governed by air temperature and its attendant effects
114
on other components of the surface energy balance, primarily net radiation
16, 22, 23
. Warmer air
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temperature in the range of weeks to months prior to ice breakup is usually the most important
116
atmospheric driver of ice breakup, in part due to its additive effects on sensible heat flux, downward
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longwave radiation, snow and ice albedo [G], and thus the total amount of absorbed longwave and
118
shortwave radiation at the lake surface
16, 22, 24
. The importance of air temperature is seen in Alaskan
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lakes, for example, where the date of the 0 ℃ air temperature isotherm, together with lake area,
120
can explain over 80% of the variation in ice breakup dates
25
. Warmer late winter and early spring
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temperatures are also correlated with earlier ice breakup in other locations
26, 27
, with lakes in more
122
southern regions experiencing the highest rates of change
18, 24
.
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124
Snow depth, shortwave radiation, and wind explain additional variation in breakup dates
15, 16, 18, 28
.
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Greater snow cover can delay ice breakup through its higher albedo and greater insulation during
126
spring, as well as the additional contribution of snowpack to lake ice thickness throughout the
127
winter
16
. However, seasonal timing is also important, since insulating snow cover in early winter
128