Ag Blog 19 July 2021
During the 2021 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 version 4.0.1 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. Additionally, soil moisture index maps of South American and western Russia are provided at the end of the blog. 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. Various other maps that help give insight into current conditions across the U.S will also be shown as needed.
This blog post was partially supported by NASA grant 80NSSC19K1266.
Order of Maps and Tables in today’s Ag Blog
- Figure 1. CONUS Soil Moisture Index map
- Figure 2a. Driest Grid Points
- Figure 2b. Wettest Grid Points
- Figure 3. U.S. Drought Monitor
- Figure 4. Flash Drought Watch update
- Figure 5. QuickDRI
While a significant percentage of the U.S. is still in drought, there is also considerably more land mass with wet soils now than a few months ago (Figs. 1-3). Note that this map is based on data through Wednesday night so precipitation that has occurred since then is not reflected in this map. Thus, it is missing what likely is considerable improvement in northern Iowa, for example. Some places in the Midwest and Northeast actually could do without precipitation for a little while and in the case of the Midwest, it looks like Mother Nature will mostly cooperate. The good news is that the relative frequency of precipitation and seasonally cooler temperatures this month in much of the Corn Belt have led to solid ratings on corn and soybean and a lack of area experiencing rapid losses of soil moisture (Fig. 4). With regard to Figure 4, it is indicating areas that had reasonable moisture three weeks ago and have since lost at least 30 percent in the root zone. Places that were already very dry (e.g., eastern ND) won’t show up.
Figure 5 shows the recent QuickDRI update. While areas in the U.S. in blue don’t automatically equate to phenomenal crop conditions, it should be interpreted that the majority of the Corn Belt is currently looking at strong yield potential. However, this was also the case at this time last year and the season had a pretty lousy finish, including the derecho last August 10th. While things are pointing up currently, it’s still too early to guarantee a record yield corn and soybean crop. More of the heart of the Corn Belt has a decent reserve of soil moisture going into late July and August, so there will be more resilience to a dry August than last year. And if the past few months are any guide, precipitation will remain adequate in the central and eastern Corn Belt and the northern part of the region will remain in drought and be more subjected to abnormal heat. One thing to watch carefully later this week into August will be more overnight temperatures across the Midwest. Regular occurrences of lows over say the low 70’s will shave off yield potential, regardless of adequate soil moisture.
If the upcoming stretch of warmer weather and dry (especially for the western Corn Belt) persists into August, corn yield likely will fall short of record territory. Significantly below trend is unlikely at this point but 2-4 points below trend would be probable if August goes more sideways than current projections show. My estimate right now is essentially what it’s been all year, a target of 180-181 with a ceiling that is in the mid 180’s and a floor in the upper 160’s.
Figure 1. The Soil Moisture Index (SMI) for the 7-day period ending 14 July 2021. 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 blue) 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 2a. Lowest 20th (10th) percentile of soil moisture as depicted by red (dark red) pixels for the week ending 14 July 2021.
Figure 2b. Highest 20th percentile of soil moisture as depicted by green pixels for the week ending 14 July 2021.
Figure 3. U.S. Drought Monitor map as of 13 July 2021. Map courtesy of the National Drought Mitigation Center.
Figure 4. Areas to watch for flash drought as of 14 July 2021. The experimental product is based on a portion of the Flash Drought Intensification Index, which was proposed in Otkin et al. (2021). The criteria are as follows: A minimum drop of -3 in the SMI over previous 3 weeks and a current SMI of < -2. In this case, the SMI is based on the 0-40 cm layers from NASA LIS. For more information, refer to Figure 1.
Figure 5. Quick Drought Response Index (QuickDRI). Figure courtesy of the University of Nebraska-Lincoln.
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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