During the 2019 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 eastern 3/4 of the U.S. where row-crop agriculture is more common. The Evaporative Stress Index (ESI) is now included in our analysis. 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 for a particular location should never be based on the SMI alone.
This blog post was partially supported by NASA grant NNH16CT05C.
Figure 1. The Soil Moisture Index (SMI) for the 7-day period ending 17 August 2019. 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. Same as Figure 1, except Noah-MP is run with a dynamic vegetation option, instead of a climatologically driven leaf area index (LAI).
Figure 3. Comparison of this week’s SMI map the last three week’s SMI maps.
The positive and negative anomalies of soil moisture index (SMI) have remained spatially consistent over most of the Corn Belt since the middle of July and this didn’t change much last week. Southern Michigan would be an exception. While much of the Corn Belt has been on the drier side since the 4th of July, the heat has mostly been absent of late and some areas in the central section of the Corn Belt have received some precipitation in the last few weeks. Several locations in eastern Iowa, Illinois, and Indiana still have experienced flash drought, but thankfully this has been a milder case than some. Of course, the yields may well be as low in some places as if it were a more significant event because of the conditions this spring.
Meanwhile in the Great Plains of Kansas, Oklahoma, and Texas, the heat has continued (not record heat, just hot) but some places started seeing some precipitation, especially in Kansas where some places west of I-35 have seen some improvement. Eastern Kansas continues to be wet. I haven’t looked at the annual totals in places like Chanute and Emporia but would have to think this has been one of the wettest years on record to date.
The dynamic vegetation continues to be more bullish over the Southern Plains and is much more bullish in the Corn Belt. A retrospective analysis shows that the dynamic vegetation simulation tends to be more aggressive with negative root zone anomalies when a dry spell or flash drought follows a pluvial.
Along the Gulf Coast, the area of negative SMI anomalies has been persistent for most of the season. I will be watching this area carefully this fall though as it wouldn’t be the first time that the region quickly went into drought in the September-October timeframe. The CPC is currently not calling for that however; actualy they are calling for removal in areas currently classified in drought in the southeast.
The 1-month ESI showed some more improvement over the Corn Belt, likely a reflection of some areas picking up beneficial rains and the lack of temperatures over 90. The ESI did decline over much of the Southern Plains and is showing particularly stressed conditions between Lubbock and Amarillo.