Volume 189: 2013 January through June Summary

The U.S. Army Corps of Engineers (USACE) 

tracks the water levels of each of the Great Lakes. 

This report highlights hydrologic conditions of 

the Great Lakes basin between January and June 

2013, evaluates what has caused water level 

extremes on Lake Michigan-Huron since 1950, 

and examines the individual hydrologic 

components of the water cycle by decade. The 

three primary Great Lakes hydrologic 

components are precipitation which falls on the 

lake surface, runoff draining to the lake, and 

evaporation from the lake surface. Runoff is 

defined as precipitation which falls on the land 

drainage area and flows to the lake.

The period of record used for each of the lakes 

includes the years 1918 to 2012 and this data has 

been coordinated between the United States and 

Canada. All 2013 water levels are considered 

provisional and will be officially coordinated in 

the spring of 2014. The elevations used are 

referenced to the 1985 International Great Lakes

Datum. The water level of each lake is averaged 

from a network of individual gages around each 

lake. Also of note is that Lake Michigan and 

Lake Huron are hydraulically treated as one lake 

due to their connection at the Straits of Mackinac.

2013 Summary: January - June

At the beginning of 2013 all of the Great Lakes 

water levels were well below their long-term 

averages. Lake Michigan-Huron’s January 2013 

monthly mean water level set an all-time record 

low of 576.02 ft. Lake Superior’s January level 

was 13 inches below the long-term average 

(LTA) and Michigan-Huron’s level was 29 inches 

below LTA. Lake St. Clair was 13 inches below 

LTA in January 2013 while lakes Erie and 

Ontario were each 7 inches below their LTA.

Seasonal changes in the weather patterns 

typically cause an annual pattern of rising and 

falling water levels. In general, each of the Great 

Lakes exhibits a seasonal rise in the spring 

primarily caused by an increase in precipitation, 

the melting of accumulated snow, and an increase 

in runoff. The seasonal decline of the water level 

in the fall and winter is primarily caused by an 

increase in evaporation and the accumulation of 

snowpack on the land area.

Since January 2013, all of the Great Lakes water 

levels have increased more than they typically do 

from January to June. Currently each of the 

Great Lakes is closer to its LTA, and Lake 

Ontario has actually risen above its LTA. 

Comparison of 2013 with Historical Record

The water level rise from January to June in 2013 

is compared with each January to June rise in the 

historical record, which dates back to 1918. The 

January to June time period does not represent 

each lake’s total seasonal rise, because the timing 

of seasonal maximums and minimums varies 

from lake to lake. This analysis is simply 

highlighting what has happened so far in 2013. 

Table 1 below shows the 2013 water level rise in

units of inches, the LTA rise, the last 10 years, 

and the 2013 ranking among the 96 years of the 

historical record. Figure 1 shows the historical

record of Great Lakes water levels.

Great Lakes

Update
Vol. 189 Great Lakes Update August 2013

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Vol. 189 Great Lakes Update August 2013

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Table 1: Great Lakes Water Level Changes from January to June (inches)

Lake

Water Level Change (June monthly mean minus January monthly mean), inches 2013 Rank Among 

Historical Record 

2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 (out of 96) LTA

(1918-2012)

Superior 8 3 2 1 8 6 -3 6 7 11 5 5

th

MichiganHuron

17 5 10 3 18 16 2 16 3 19 9 5

th

St. Clair 17 2 10 1 15 12 13 29 -2 18 13 24th

Erie 17 4 11 -1 16 16 13 30 -7 16 13 32nd

Ontario 12 11 10 0 25 16 13 33 4 28 19 13th

There were noticeable dry periods in the years 

2005 and 2007 across all of the Great Lakes for 

the January through June time period. In these 

two years, all of the lakes were below their 

typical water level rises. There were significant

wet periods in the years 2008 and 2011, where 

the January to June changes for all of the Great 

Lakes were greater than their typical rises.

Although the first half of 2010 was a very dry 

period for lakes Superior and Michigan-Huron, 

the water level changes for St. Clair and Erie 

matched their averages. Lake Ontario rose less 

than the typical amount in 2010. The 2010 

example shows how the hydrologic conditions 

can be different from one Great Lake basin to 

another.

There are also significant changes which occur 

from year to year. For example, 2007 and 2008 

exhibited very different behavior for each of the 

Great Lakes. Likewise, 2010 to 2012 were also 

very different in their January to June water level 

changes from one year to the next.

The 2012 January to June water levels rose more 

than the typical amount for Lake Superior. 

However, all of the other Great Lakes exhibited 

very low water level changes. Lakes St. Clair and 

Erie actually dropped during the January to June 

time period, exhibiting differences below average

of 15 and 20 inches, respectively. Lake MichiganHuron’s very low spring rise in 2012 was one of 

the factors which led to the all-time record low 

water level in January 2013.

The last column of Table 1 shows the comparison 

between 2013 and the historical record. The 2013 

January to June rise was the 5th highest for both 

Lakes Superior and Michigan-Huron, 24th highest 

for Lake St. Clair, 32nd highest for Lake Erie, and 

13th highest for Lake Ontario.

2013 Net Basin Supplies

Water level changes are primarily determined by 

the balance of the following factors: precipitation 

falling on the lake surface, runoff draining to the 

lake, evaporation from the lake surface, 

diversions into or out of the lake, and connecting 

channel inflows and outflows. The Net Basin 

Supply (NBS) is an important quantity for 

understanding the amount of water which arrives 

to the lake. USACE uses the residual method to 

compute NBS which is equal to the water level 

change, minus the inflow from an upstream lake, 

plus the outflow, and plus any diversions out 

of (+) or into (-) the lake. Altogether, NBS 

represents the combined effects of precipitation, 

runoff, and evaporation. NBS is far and away the 

main driver of water levels.
Vol. 189 Great Lakes Update August 2013

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Each lake’s NBS was totaled for the months of 

January through June. The NBS totals for 

January through June 2013 were greater than the 

historical averages for all of the Great Lakes. 

The NBS totals for each lake are shown in 

Table 2 in units of inches of water over the lake 

surface. The historical record of NBS uses a 

period of record of 1900 to 2008 for all of the 

Great Lakes except Lake Ontario. The Lake 

Ontario NBS period of record is 1900 to 2005. 

Table 2: Great Lakes Net Basin Supply Totals 

from January to June (inches over the lake)

Lake 2013 LTA (1900 – 2008)**

Superior 23 19

Michigan-Huron 34 27

St. Clair* 238 107

Erie 38 32

Ontario 56 51

*The smaller surface area of Lake St. Clair causes the NBS totals to be 

distorted when looking at the depth of water on the lake surface.

**The Lake Ontario average NBS is based on period of 1900 – 2005.

The Great Lakes have experienced some 

extremely wet NBS amounts in specific months 

of 2013. In particular, Lake Superior’s NBS was 

the 2nd highest ever for the month of May in

2013. Lake Michigan-Huron’s NBS was the 2nd

highest ever for the month of April in 2013. 

Lakes St. Clair and Erie experienced an 

extremely wet June, with their highest ever NBS 

amounts for the month of June in 2013. The Lake 

Ontario NBS was the 4th highest ever for the 

month of June in 2013.

Hydrologic Components by Decade

To further understand the fluctuations in Great 

Lakes water levels, this section examines the 

three primary hydrologic components of the 

water balance over the past six decades; namely 

precipitation, runoff, and evaporation. The 

annual totals of each component were computed 

and then the totals for each year were averaged by 

decade: 1950 to 1959, 1960 to 1969, etc. The 

period of record of coordinated precipitation data 

spans 1900 to 2010. Runoff and evaporation data 

used here comes from the National Oceanic and 

Atmospheric Administration Great Lakes 

Environmental Research Laboratory (GLERL). 

Runoff data was computed by GLERL using an 

area-weighted approach of extrapolating gauged 

drainage areas. Evaporation estimates are from 

GLERL’s Large Lake Evaporation and 

Thermodynamics Model which has recently been 

updated in 2013. This analysis begins in 1950 

because that is the earliest that all three data sets 

are available. Prior to 1950, there is insufficient 

data which is required for the evaporation model. 

All data has been converted to an equivalent 

depth of water on the lake’s surface.

Figures 2 through 6 show the decadal averages of 

annual precipitation, annual runoff, and annual 

evaporation for each lake over the past six 

decades. These figures offer a large time-scale 

perspective of the component estimates. Specific 

annual totals may vary significantly from their 

decade’s average.

One observation from the figures below is the 

relative influence of each component varies from 

lake to lake. For lakes St. Clair and Ontario, 

runoff is more influential than precipitation and 

evaporation due to the large ratio of drainage area 

to lake surface area. Another observation is that 

the transition from the lower water levels of the 

60’s to the higher water levels of the 70’s and 

80’s was driven by a general increase in 

precipitation and runoff for all of the lakes during 

that time period, with the exception of Lake 

Superior’s estimated runoff being low in the 80’s.

The figures also show that evaporation has 

generally increased on the Great Lakes from the 

1960’s to the 2000’s. Lakes Superior and 

Michigan-Huron exhibited an especially large 

jump from the 1990’s to the 2000’s. This is a 

large contributing factor to these two lakes being 

in a consecutive 14-year period of below average 

water levels, the longest stretch in each of their 

recorded histories.
Vol. 189 Great Lakes Update August 2013

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Vol. 189 Great Lakes Update August 2013

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Causes of Water Level Extremes on Lake 

Michigan-Huron Since 1950

The water level of Lake Michigan-Huron set a 

new all-time record low in January 2013 at a 

water level of 576.02 ft, breaking the previous 

record low water level of 576.05 ft set in March

of 1964. This section looks at periods of high and 

low Michigan-Huron water levels over the last 60 

years and examines the primary contributing 

factors leading to the water level extremes.

The three periods of interest are 1955 to 1964, 

1965 to 1997, and 1998 to present. As seen in 

Figure 1, Lake Michigan-Huron experienced 

record low water levels in the first time period 

(1955 to 1964), record high water levels in the 

second time period (1965 to 1997), and low water 

levels again in the third time period (1998 to 

present). Due to its very large size, extreme 

water levels on Lake Michigan-Huron are not 

caused by a single storm, but rather by 

consecutive seasons or years of persistent wet or 

dry conditions.
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Vol. 189 Great Lakes Update August 2013

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The primary hydrologic components are shown in 

Figures 7 – 9 to highlight the causes of extreme 

water levels in the above-mentioned time periods. 

The annual data for each component is converted 

to an equivalent depth of water over the lake 

surface. The data is shown relative to the annual 

average, so positive values indicate above 

average quantities and negative values indicate 

below average quantities. The sources of data are 

the same as mentioned in the previous section 

“Hydrologic Components by Decade”. As noted 

there, the evaporation data set is only available 

back to 1950.

In the 1955 to 1964 time period, there are some

important features which are noticeable, 

particularly in Figures 7 and 8. Precipitation 

totals and runoff totals are clearly well below 

average in this time period. Over the 10 

consecutive year period, there are 8 years with 

below average precipitation and 9 years with 

below average runoff. Further, both of the two 

lowest annual precipitation totals are in this 

period and the three lowest annual runoff totals 

occur in this time period. The persistently below 

average amount of precipitation and runoff is the

primary cause of the record low levels of 1964.

All three hydrologic components contributed to 

high water levels in the 1965 to 1997 time period. 

Precipitation was above average for 26 out of the 

33 consecutive year period and runoff was above 

average for 25 out of 33 years. Evaporation was 

below average in this time period for 24 out of 33 

years. In fact, the 10 lowest evaporation totals all 

occurred in the period from 1965 to 1997. The 

year 1985 recorded the highest annual 

precipitation and runoff. The persistently wet 

conditions led to high water levels throughout this 

period with the record high water level occurring 

in 1986.

An interesting transition occurred in 1998 as the 

annual runoff dropped and the annual evaporation 

rose. The three-year period of low runoff and

high evaporation from 1998 to 2000 caused the 

Michigan-Huron level to plummet, as can be seen 

in Figure 1. This was the beginning of the current 

14 consecutive year stretch of below average 

water levels for Lake Michigan-Huron, the

longest in its recorded history. Evaporation is the 

primary cause of the ongoing low water levels, as

is evident in Figure 9. Evaporation has been 

above average since 1998 and the four highest 

annual evaporation totals all occurred between 

1998 and the present. One of the primary factors 

in determining evaporation is water temperature, 

and annual Michigan-Huron water temperatures

have been above average since 1998.

More Information

The Detroit District recently migrated to a new 

website. The website address for the Detroit 

District home page remained the same, but links 

to specific pages have changed. Below is a list of 

links which may be of interest:

Home page: http://www.lre.usace.army.mil

Great Lakes Information: http://www.lre.usace.a

rmy.mil/Missions/GreatLakesInformation.aspx

Water Levels & Forecasts: http://www.lre.usace.a

rmy.mil/Missions/GreatLakesInformation/Great

LakesWaterLevels.aspx

The Detroit District welcomes comments on all of

our forecast products. Please email questions and

comments to hhpm@usace.army.mil. To contact

the District by phone call toll free 1-888-694-

8313 and select option 1. To receive the Monthly 

Bulletin by postal mail, please email us or call us 

with the contact information just mentioned. The 

Detroit District’s mailing address is:

Department of the Army

Detroit District Corps of Engineers

ATTN: CELRE-HH-W

477 Michigan Avenue

Detroit, MI 48226