During the 2020 growing season, 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 of the SMI over the four regions of U.S. where the majority of corn, soybean, wheat, and cotton 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. Remote sensing based products such as The Evaporative Stress Index (ESI) are also included in our analysis (when available) 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
- Figure 1. Soil Moisture Index Panel (U.S., southern Canada, northern Mexico)
- Table 1. Regional Soil Moisture
- Figure 2. SMI over the past four weeks
- Figure 3. NASA Gravity Recovery and Climate Experiment root zone soil moisture
- Figure 4. 30-day Precipitation percent of normal
- Figure 5. Evaporative Stress Index
- Figure 6. Vegetation Drought Response Index
- Figure 7. Quick Drought Response Index
As of last Friday, the drought across the Western Corn Belt continued to intensify and expand further south and east (Figures 1-3; Table 1). The ESI map (Figure 5) from yesterday shows a clear “bullseye” of drought-stressed vegetation over west-central Iowa. VegDRI and QuickDRI maps (Figures 6-7) are a bit dated but both have done a very nice job of capturing where the biggest impacts to corn and soybean are likely. For a more in-depth analysis of the drought, please see last week’s Ag Blog. The good news is the current system in the central U.S. is bringing much needed moisture to places that have been lacking in moisture over the last several weeks and next week’s map is likely to look much different. While this rain is too late to be helpful to the crops, significant recharge of soil moisture going into the cold season is important. Much of this region affected by drought in the Corn Belt does not necessarily get enough precipitation to erase large root zone soil moisture deficits over the winter, so significant recharge this week may be helpful for the next crop. Another upside is this is occurring now and not in a few weeks, which could set back harvest.
Storms early last week brought significant moisture to the 1-40 corridor (Fig. 4), with high SMI values the rule from central Oklahoma eastward to the Atlantic Ocean. Much needed rain also fell last Tuesday over parts of the central Corn Belt, though it was not enough in most cases to significantly bring up the SMI. But it may have been just in time to give a needed boost to soybean and later-planted corn. Much of Ohio and Pennsylvania still had negative SMI values but there was definite improvement over the previous weeks (see Fig. 2). Same story with the SMI the New England states, though the GRACE product (Fig. 3) still indicates significant dryness over this region.
Much of the west remains very dry and the record heat the past several days isn’t helping matters. Note that the higher SMI values in California are reflective of marginally better than average soil moisture, which in early September honestly doesn’t mean anything. Fires will continue to be an ongoing concern, even in places where the SMI is positive. The drought in the High Plains also had a significant toll on pasture condition, with GrassCast projecting a 30 percent reduction in grass production over much of eastern Colorado and eastern New Mexico.
Figure 1. The Soil Moisture Index (SMI) for the 7-day period ending 4 September 2020 (top left) and 27 August 2020 (bottom left). On the right hand side are the grid points where the SMI is at or above 3.0 (top right, green) and grid points where the SMI is at or below 3.0 (bottom right, red). 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.
Table 1. The regional median SMI value from the current map and the percentage of grid points in the four regions with SMI values greater than 3.0 and less than -3.0. Regions are indicated by the boxes in Figure 1.
Figure 2. SMI map from this week (upper left) and the previous three weeks: 27 August (upper right), 20 August (lower left), and 13 August (lower right).
Figure 3. NASA Gravity Recovery and Climate Experiment (GRACE) root zone soil moisture percentiles. More information on the product can be found here.
Figure 4. Percent of normal precipitation over the past 30 days (through Monday 7 September). Map courtesy of the High Plains Regional Climate Center.
Figure 6. The Vegetation Drought Response Index over croplands in the U.S. Map courtesy of the University of Nebraska-Lincoln. Additional information can be found here.
Figure 7. The Quick Drought Response Index courtesy of the University of Nebraska-Lincoln. Additional information can be found here.
According to the latest Crop Progress Report, 61 percent of corn is rated Excellent/Good (E/G) vs. 14 percent Poor/Very Poor (P/VP), about where it was last week. A quarter of Iowa corn is rated as P/VP but the other major corn producing states generally have 10 percent or less in P/VP. A quarter of the corn crop has reached maturity and 80 percent is in dent stage. Both numbers are slightly above the 5-year average. Soybean condition is about the same as last week with 65 percent E/G vs. 10 percent P/VP, and leaves are starting to drop in most states. Cotton continues to be in good to fair condition, with poorest conditions across Texas where drought has been the rule this season.
About the author:
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. He can be reached via email at firstname.lastname@example.org and @DroughtLIS on Twitter.
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