over Northern Illinois Continues
Researcher: Bob Scott, Climatoligist,
(217) 333-4966, email@example.com,
By: Eva Kingston, (217) 244-7270, firstname.lastname@example.org
With precipitation totals six inches below typical amounts
over the last seven months, 69 percent of average, Illinois has
the seventh driest September–March period since 1895, and
the driest such period over the last 46 years, according to the
Illinois State Water Survey (http://www.sws.uiuc.edu), a division
of the Illinois Department of Natural Resources.
Regional precipitation conditions in Illinois for September–March
also have been very dry. The northwest and northeast Crop Reporting
Districts (CRDs) were the driest on record (50 and 52 percent
of average, respectively). The west and central CRDs were the
second driest (57 and 53 percent of average, respectively). The
east CRD was fourth driest (57 percent of average). With 73 and
77 percent of average, respectively, the west-southwest and east-southeast
CRDs were the 15th driest. Precipitation has been near average
to above average in the southwest and southeast CRDs, and they
are not currently experiencing a deficit.
Technically, these data place the northern half of Illinois
in a climatological precipitation drought, and impacts are beginning
to be observed in other water resources of the state. Surprisingly,
soil moisture conditions within the uppermost six inches of soil
are relatively near average across Illinois, but sub-soil moisture
conditions vary considerably. Observations from the southern
third of the state indicate above average moisture levels between
40 and 72 inches below the surface, but conditions in parts of
central and northern Illinois in this layer are only 25 percent
Without a large snowmelt this year, combined with the low precipitation,
streamflows along selected rivers and streams are showing below
to much below normal flows for this time of year in all but extreme
southern Illinois. Overall, current statewide flows are just
37 percent of the median flow rates for the end of March and
have been below median rates since last October.
Shallow groundwater water table levels in observation wells
away from pumping stations are also well below average levels
have been below the statewide average for the last seven months.
Overall, shallow groundwater levels were below average levels
for March by 2.2 feet. In northern Illinois, the well at Mt.
Morris (Ogle County), where readings began in 1961, reported
a record low for March, and the well at Fermi Laboratory (DuPage
County) reported the lowest monthly level in the 15 years of
observation at that site.
Reservoir data have shown only slight impacts from low precipitation
totals, primarily because there are no public water reservoirs
in the northern third of the state. Some northernmost reservoirs
are below normal levels by a few feet, not considered a concern
at this time, but these conditions should be monitored closely
for those reservoirs not filled by the end of April.
Reduced precipitation is not only present in Illinois, but
also over much of the Midwest. Consequently, the water level
Michigan this spring is at its lowest since 1964. The lake is
two feet below the normal for April and only eight inches above
the record low level observed in 1964.
Fortunately, the precipitation deficit has occurred during
a period when monthly rainfall totals in northern and central
are typically low, crops are not using water, and evaporation
rates are considerably lower than in warmer seasons. Thus, the
primary potential impact of the precipitation deficit currently
is on agriculture. Above average rainfall over the next several
months is needed to recharge sub-soil moisture in dry areas as
crop roots begin to tap into these depths later in the summer.
However, without a return to average precipitation, rapid reductions
in other water resources within the northern half of Illinois
may soon follow.
If history is a guide, only two years of the remaining years
in the top 10 driest September–March periods had slightly
above average statewide precipitation amounts in the April–June
period that followed (14 and 18 percent above average). Six of
the years observed slightly below average rainfall (6 –16
percent below average), and precipitation in Illinois within
the following three months was less than 50 percent of average
For more information on current precipitation conditions in
Illinois see the following Web sites: http://www.sws.uiuc.edu/warm
(more specific data on soil moisture), and http://www.drought.unl.edu/dm/monitor.html
(U.S. drought monitor).