VegDRI: A view of Illinois corn and soybean crops from space

There is a new way to look at drought stress in Illinois – from space. Called VegDRI, this product integrates “satellite-based observations of vegetation conditions, climate data, and other biophysical information such as land cover/land use type, soil characteristics, and ecological setting. The VegDRI maps that are produced deliver continuous geographic coverage over large areas, and have inherently finer spatial detail (1-km resolution) than other commonly available drought indicators such as the U.S. Drought Monitor,” according to the VegDRI website.

In other words, it looks at crop stress as it relates exclusively to drought. The maps are updated every two weeks.

The August 22, 2011, map below shows that crops in much of western and central Illinois are showing much stress from the lack of rain and high temperatures in July and August. If you go to the VegDRI website, you can see a national map. Click on a state to get a closer view. Scroll down the state page and click on the quadrant map of  the state so see even more detail.

VegDRI map for Illinois for August 22, 2011.
VegDRI map for Illinois for August 22, 2011. Click to enlarge.
VegDRI map for east-central Illinois
VegDRI map for east-central Illinois for August 22, 2011. With this level of detail, changes within a county are easily seen. Click to enlarge.

The National Drought Mitigation Center produces VegDRI in collaboration with the US Geological Survey’s (USGS) Center for Earth Resources Observation and Science (EROS), and the High Plains Regional Climate Center (HPRCC), with sponsorship from the US Department of Agriculture’s (USDA) Risk Management Agency (RMA). Main researchers working on VegDRI are Dr. Brian Wardlow and Dr. Tsegaye Tadesse at the NDMC, and Jesslyn Brown with the USGS, and Dr. Yingxin Gu with ASRC Research and Technology Solutions, contractor for the USGS at EROS.

Extreme Dryness in August for Much of Illinois

While the rains continue in northeastern Illinois, much of the rest of the state has been bone dry in August. Rainfall totals range from 3-5 inches in the Chicago area to less than an inch in many locations across central and southern Illinois. This band of dryness extends from southern Minnesota, eastern Iowa, Illinois, and into parts of Indiana and Kentucky (see first map).

Rainfall departures  are on the order of 1-2 inches below average in the driest areas. Some of those same areas received little rainfall in July. The US Drought Monitor has much of central and southern Illinois in at least “moderately dry” with “moderate drought” in the central region of the state.

Of particular concern to me is that the few opportunities for substantial rain in August across central Illinois have resulted in only scattered showers/thunderstorms at best. There is another chance of rain on Tuesday/Wednesday but the projected amounts are on the order of 0.25 inches or less.

Update: USDA, National Ag Statistics Service (NASS) released the following on Illinois topsoil moisture (percent) by crop reporting district:

District Very Short Short
 Northwest  4  21
 Northeast  –  18
 West  49  44
 Central  31  38
 East  40  44
 West Southwest  26  58
 East Southeast  13  46
 Southwest  20  40
 Southeast  30  56
 State  25  41
Rainfall across the Midwest for August 2011
Rainfall across the Midwest for August 1-22, 2011 (source: Midwestern Regional Climate Center). Click to enlarge.
Precipitation departure in the Midwest for August 2011
Rainfall departure from average in the Midwest for August 1-21, 2011 (source: Midwestern Regional Climate Center). Click to enlarge.

New Climate Normals for Illinois

The new 1981-2010 climate normals are available for Illinois. You can find them through a station list or a Google Map on my homepage.

Climate normals are 30-year averages that are updated every 10 years in the U.S. The National Climatic Data Center produces the climate normals for the US. By settling on a standard averaging period, users are able to compare climate conditions between two or more locations.

By updating every 10 years, the climate normals can reflect data from newer stations as well as reflect any changes to the climate.  One impact of switching from the 1971-2000 to the 1981-2010 climate normals was that the cold, snowy winters of the 1970s fell out of the calculations. As a result, the new normal snowfall has dropped a little in most places. For example, the new normal annual snowfall is 3 inches less in Champaign-Urbana.

The National Climate Data Center has a climate normals page dedicated to the new climate normals and frequently asked questions.

Drought Arrives in Central Illinois

The U.S. Drought Monitor had introduced D1 “moderate drought” into central Illinois. This is based primarily on very low rainfall totals of less than an inch in the last 30 days in this region, combined with temperatures that were 4 to 5 degrees above normal. The Illinois Ag Statistics Service note that the topsoil moisture was “very short” in:

  • the West Crop Reporting District (CRD) at 38%
  • the Central (CRD) at 14%
  • the East (CRD) at 51%
Drought monitor for Illinois
The U.S. Drought Monitor for Illinois on August 11, 2011. Click to enlarge.
30 day rainfall
30-day rainfall for the Midwest, ending August 10, 2011. Source Midwestern Regional Climate Center. Click to enlarge.

July Rainfall in Illinois Varied from Too Dry to Too Wet

The statewide average rainfall for July in Illinois was 4.12 inches, only 0.29 inches above average. However, rainfall across the state varied widely from too dry to too wet.

Rainfall amounts in the northern third of the state were impressive with widespread areas in excess of 6 to 8 inches. The heaviest rains fell around Galena. A CocoRaHS observer (IL-JD-2) reported a monthly rainfall total of 19.21 inches while the nearby Galena NWS Coop observer reported 17.78 inches. In nearby towns:

  • Elizabeth reported 16.74 inches (NWS),
  • Freeport reported 12.08 inches (CoCoRaHS), and
  • Mt. Carroll reported 11.33 inches (NWS).
Chicago O’Hare airport had a July rainfall total of 11.15 inches, their wettest July on record, thanks largely to the 6.86 inches that fell in three hours on July 23.

The middle third of Illinois was exceptionally dry. Some of the smaller rainfall totals for July were just south and west of the heavy rainfall in northwest Illinois. One of the drier sites was Aledo with only 0.55 inches. Amounts of only 1 to 2 inches were common in central Illinois. This equates to rainfall departures that were generally 50-75 percent of average (or worse) across the region. Champaign-Urbana experienced its 20th driest July on record with only 1.58 inches, 3.12 inches below average. Springfield reported 1.09 inches and Peoria reported 1.66 inches.

The southern third of Illinois was wet, where amounts of 4 to 8 inches or more were common. The largest July rainfall total was at the NWS Du Quoin site with 8.88 inches.

July 2011 rainfall in Illinois
July 2011 rainfall in Illinois. Click to enlarge.
July 2011 rainfall departure for Illinois
July 2011 rainfall departure from average for Illinois. Click to enlarge.

Sixth Warmest July on Record for Illinois

It comes as no surprise that this July was one of the warmest on record. The statewide average temperature for Illinois was 80.1 °F. That is 4.3 °F above average and the 6th warmest on record (tied with 1955). Here is how the top six Julys look:

  1. 83.1 in 1936
  2. 81.7 in 1901
  3. 81.3 in 1934
  4. 80.4 in 1916
  5. 80.2 in 1921
  6. 80.1 in 2011 and 1955

While the daytime temperatures were impressive, it was the very warm nighttime temperatures that pushed this July into the top 10 list. Here in Champaign-Urbana, we were the 7th hottest July in terms of daytime high temperatures but we were the 2nd hottest July in terms of nighttime low temperatures. Why so hot, especially at night? The high humidity levels experienced in July prevented the nighttime temperatures from cooling off.

Looking at stations with records of at least 30 years, we had 168 broken and 71 tied daily record high low temperatures. Meanwhile we had only 28 broken and 24 tied record daily high temperatures.

At least 38 sites reported temperatures reaching the 100°F mark. The hottest temperature reported for July was 105°F at Dixon Springs on July  13 and Streator on July 25.

Does this July indicate climate change?

Below is the graph of July temperatures for Illinois from 1895 to present. While July 2011 was outstanding compared to recent decades, we have had other stretches of hot Julys. In my opinion, the most interesting feature is the dramatic rise in July temperatures in the 1920s and first half of the 1930s that maximized in 1936 before returning to values closer to the long-term average.

As the shading indicates, we were more often warmer than average (red shading) in the first half of the 20th century. We were more often cooler in the second half of the 20th century and in the early 21st century. Another thing to note is that 2009 was the coldest July on record for Illinois with an average of only 70.2°F and now this year with the 6th warmest.

At this point, this July does not indicate a pattern of hotter summers in July. The large year to year variability as well as the tendency for trends of up to 10 years to appear and disappear show just how hard it is to detect long-term (i.e., multi-decade) climate change in the Illinois records for summer.

July temperature for Illinois
July Temperature, Average for Illinois from 1895 to 2011. The arrow denotes 2011. The long term averages (1895-2010) is shown as a horizontal line in the middle of the chart. Five-year moving averages are plotted in comparison to the long-term average and shaded as red (above average) or blue (below average) curves. Click to enlarge. Source: Southern Climate Impacts Planning Program.