Ag Blog Update 12 May

Ag Blog Update 12 May


During the 2020 growing season, Dr. Eric Hunt of Atmospheric and Environmental Research, Inc. will be providing weekly updates of the soil moisture index (SMI) from the Noah-MP land surface model in the NASA LIS framework for the entire U.S. and regional analysis over the Corn Belt in the north central U.S. where the majority of corn and soybean production occurs. The analysis is intended to provide the larger agricultural and meteorological communities insight as to areas where soil moisture is excessive or deficient compared to average for that location and what that may mean for impacts. It is my goal that these maps can be an early warning signal for flash drought development or where flash flooding could be likely in the coming week if heavy precipitation materializes. Please be advised that the SMI should be viewed as complementary, not a substitute, to the U.S. Drought Monitor (USDM) and that declarations of drought or flash flood potential for a particular location should never be based on the SMI alone. The Evaporative Stress Index (ESI) is also included in our analysis as are various other maps that help give insight into current conditions across the U.S.

This blog post was partially supported by NASA grant 80NSSC19K1266

Order of Maps and Tables in today’s Ag Blog

  1. Figure 1. Soil Moisture Index Panel (U.S., southern Canada, northern Mexico)
  2. Figure 2. U.S. Drought Monitor monthly change
  3. Figure 3. Corn Belt Region Soil Moisture Index
  4. Table 1.  Corn Belt Region Median Soil Moisture Index
  5. Table 2.  Percent Corn Planted and Emergence
  6. Figure 4. Evaporative Stress Index
  7. Figure 5. Spring Freeze Map


Cooler weather was the rule over much of the eastern 2/3 of the U.S. last week with sub-freezing temperatures affecting sections of the Corn Belt (more on that later). Most of the U.S. is neither excessively wet or dry, though there are pockets of concern on the dry side. Those include the coastal areas of northern California and southern Oregon, across the southern High Plains, and south Texas (Figure 1). The good news is precipitation over the last several weeks has greatly improved conditions in the eastern Gulf Coast and middle Atlantic region, in good agreement with the latest 1-month change map of the U.S. Drought Monitor (Figure 2).

Figure 1. The Soil Moisture Index (SMI) for the 7-day period ending 7 May 2020 (top left) and 9 April 2020 (bottom left). On the right hand side are the grid points where the SMI is at or below -4.0 (top right, red) and grid points where the SMI is at or above 4.0 (top right, green).  Results are based on output from the 0-1 m (surface to 3.23 feet) layers in the Noah-Multiparameterization (Noah-MP) land surface model. Noah-MP is run in the NASA Land Information System (LIS) framework with the North American Land Data Assimilation Version 2 (NLDAS-2) forcing dataset. The SMI calculation is based on the soil moisture index created in Hunt et al. (2009) such that ‘5’(dark green) is the wettest and ‘-5’ (dark red) the driest for the period of record.  The period of record used calculate the SMI for the current map is 1979-present.



Figure 2. U.S. Drought Monitor class change courtesy of the National Drought Mitigation Center.


The last month has generally been on the cool and dry side across the majority of the Corn Belt with most locations having SMI values under 0 and in parts of Iowa, Minnesota, and Nebraska, the SMI has fallen below -3.0 (Figure 3). The median SMI values are less than 0.0 across the Northern, Western, and Eastern Corn Belt (Table 1).

If this was the middle of July this may be cause for concern but to this point the recent dryness has probably been somewhat beneficial. First, this likely helped reduce the flooding risk along area rivers and streams, which seemed to be a big threat three months ago. Second, the drier weather has allowed for accelerated planting over the past few weeks, with the percentage of corn planted and emerged being right around the median of the past 40 and 20 years respectively (Table 2) and ahead of the 5-year average for both. Third, the forecast is for warmer and wetter conditions for much of the region, including across eastern Nebraska and northern Iowa where SMI values are currently lowest. If this forecast comes to fruition, this should bring root zone soil moisture levels back around normal for mid-May.

Figure 3.  Analysis of the SMI by region of the Corn Belt. The median SMI values for each region are located above. Regions are as follows: N (Northern), W (Western), C (Central), E (Eastern), S (Southern). The majority of U.S. corn production is from these regions and the regions were set to avoid high-density areas of irrigation (e.g., central Nebraska).


Table 1. The median SMI value from the current map, last week’s map, and one year ago at this time over the five regions of the Corn Belt.


Table 2. The percent of corn that has been planted and has emerged across the U.S. according to the latest USDA Crop Progress Report.  Period of reference for planted and emerging corn are 1980-2020 and 1999-2020 respectively.

The Evaporative Stress Index (ESI; Figure 4) is not available everywhere in the U.S. yet (out of season mask indicated in white) and at this point of the season, negative values may not necessarily be indicative of drought stress on vegetation. The areas in the U.S. most worth watching as we move into June are the High Plains of eastern Colorado, Kansas, and the western panhandle of Oklahoma and into northern California and southern Oregon. The negative values across the Highway 20 corridor from Nebraska into Iowa are also concerning but may be more reflective of a lack of tree foliage and lusher grass compared to normal. However, if the signal persists across northeastern Iowa for the next several weeks after rain and warmer weather, that is a good indication that last weekend’s freeze may have been detrimental enough to cause replanting. The latest spring freeze map from the Midwestern Regional Climate Center (Figure 5) shows that much of the upper Midwest dropped to 28°F on Saturday morning. Perhaps the best news is that most of the places where sub-freezing temperatures occurred are also the places where season-to-date accumulated growing degree days (GDD’s) have been lowest. Still this area should be monitored closely over the next few weeks.

Figure 4. 1-month Evaporative Stress Index (ESI) from 9 May 2020. For additional information on the ESI, please refer to Anderson et al. (2012) and Otkin et al. (2013)


Figure 5. Date of last freeze (28°F) for the central U.S.


About the author:


 Dr Eric Hunt is an agricultural climatologist from Lincoln, NE and has several members of his extended family actively farming in Illinois and Nebraska. Eric has been with AER since 2012 and received his Ph.D. from the University of Nebraska. Among other activities, he is currently working on NASA funded projects to study the evolution of flash drought. He routinely blogs about agriculture and weather on the AER website.

About AER:

Founded in 1977, Atmospheric and Environmental Research is an award-winning environmental research, consulting and weather information services company with demonstrated expertise in numerical weather prediction, climate dynamics and radiation, circulation diagnostics, atmospheric chemistry, air quality and risk assessment, planetary sciences, remote sensing, satellite meteorology, and systems engineering. Consulting services are available. AER is a business unit of Verisk Analytics (VRSK). For more information, please visit our web site at

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