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. SPoRT LIS map
- Figure 4. 30-day Precipitation percent of normal
- Figure 5. Evaporative Stress Index
- Figure 6. Vegetation Drought Response Index
- Figure 7. Soil Moisture Index vs. Corn Trend
I would like to start the blog today by offering my sincere condolences to all farmers and others affected by last Monday’s derecho that moved through several midwestern states, especially to those over the hardest hit area of central Iowa. Staying in the state of Iowa, the U.S. Drought Monitor shows varying levels of drought over the western half of the state, with a large pocket of extreme drought to the northwest of Des Moines. As has been the case for several weeks, the soil moisture index (SMI; Figures 1-2; Table 1) is strongly negative over the western half of Iowa and across the river into northeast Nebraska. Some rain has fallen in most of the drought area over the past week, including some decent rains in eastern Nebraska since the cutoff for this map. But for the most part it’s not enough to make a dent in the precipitation deficits (Fig. 4) or the drought. As I posed last week, the other million dollar question right now is “How much impact has the flash drought had?”
There is a bit more agreement between VegDRI (Fig. 5) and the Evaporative Stress Index (Fig. 6) than over the past week, though VegDRI continues to be much more bullish on moderate to severe drought than the ESI is over the western Corn Belt. Unfortunately there was not a new QuickDRI map as of 18:00 EDT on Monday to be included in the blog, but the hyperlink will show you the latest update should it be posted by Tuesday. I will continue to maintain that drought impacts to the corn over that part of Iowa are less significant than what may be expected but that is not to say there are no impacts. The upcoming forecast is not particularly helpful on the moisture side, though a lack of heat should help keep evaporative losses lower and the cooler nights will benefit the grain filling. Past evidence would suggest that dry and cool is not necessarily a bad thing, though at this point it could be a race to see how well kernels can be formed and filled on ears before water stress becomes too severe.
The southern part of the Corn Belt from northeast Kansas into downstate Illinois is quite moist and I would expect record yields for many locations in that area, assuming there isn’t another strong derecho. The area just to the east of the Corn Belt in eastern Ohio and Pennsylvania has had very low SMI values for several weeks now and the ESI is indicating vegetation stress at severe levels. Note that the current ESI and previous QuickDRI analysis are more bullish on drought in western and central Pennsylvania than over western and central Iowa. Remnants from Isaias continued to be apparent over parts of the northeast while the Mid-Atlantic region is wet in general, which is a rather stark reversal over earlier this summer. Outside of the areas affected by Isaias, much of New England remains on the dry side, with negative SMI values over most of the six-state region.
SMI values are also quite low over much of the western U.S., which isn’t going to be helped by the upcoming heat this week. Texas also continued to have low SMI values over most of the state and this area extends to the north and west along the western High Plains of Colorado. Some deterioration has been noted again over parts of North Dakota. The southeastern U.S. continues to be a mix of wet and dry soils. Thankfully there are no large areas of flash drought to report at this time, though extreme west Tennessee and the southern parts of Alabama and Georgia are certainly very dry and should be watched going forward.
Figure 1. The Soil Moisture Index (SMI) for the 7-day period ending 13 August 2020 (top left) and 6 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. In the median column, red(blue) font indicates a decrease(increase) of more than 1.0 over the previous week. In the percentage columns, red font is used to indicate a region where the percentage of grid points ≤ -3.0 increased by more than 10 points and blue font is used to indicate a region where the percentage of grid points ≥ 3.0 increased by more than 10 points.
Figure 2. SMI map from this week (upper left) and the previous three weeks: 6 August (upper right), 30 July (lower left), and 23 July (lower right).
Figure 3. 0-100 cm percentiles from the NASA Short-term Prediction Research and Transition Center (SPoRT) LIS simulation from 00Z on 17 August 2020.
Figure 4. Percent of normal precipitation over the past 30 days (through Sunday 16 August). 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. Median soil moisture index (SMI) at Week 30 from 1979-2020 and corn yield trend represented by the colored markers. Categories: Dark Blue > 10%, Blue +5 to 10%, Light Blue +1 to 5%, Gray -1 to 1%, Light Red -1 to -5 %, Red -5 to 10%, Dark Red <-10%.
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 email@example.com and @DroughtLIS on Twitter.
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 www.aer.com.