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 10 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, with some additional degradation in northeast Nebraska. Recent rainfall (i.e., past the data cutoff for this map) have likely helped. While much of the Corn Belt has been on the drier side the past 30-45 days, the heat has mostly been absent since the stretch of excessive heat a month ago. The lack of very warm daytime highs has been a saving grace in places like eastern Iowa and western Illinois from more rapid intensification of flash drought.
Further to the south, it is a different story. Up until very recently, rainfall had been mostly absent from Kansas into Texas along and west of I-35 since June, and temperatures have been routinely been upper 90’s to mid 100’s of late. The dynamic vegetation simulation is more bullish on the magnitude of the developing flash drought than the Noah-MP run, but it is definitely showing stress too. Along the Gulf Coast, the area of negative SMI anomalies has been persistent for most of the season. Thankfully the more severe anomalies have remained in “pockets” as opposed to developing into a region wide flash drought, as has happened in the past. I will be watching that 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; actually they are calling for removal in areas currently classified in drought in the southeast.
The 1-month ESI showed some improvement over the Corn Belt, likely a reflection of some areas picking up beneficial rains and the lack of temperatures over 90. The ESI remains positive over much of the SGP that is experiencing flash drought but that might be a reflection that the majority of native vegetation hasn’t experienced significant impacts- yet. I fully expect the ESI to start showing more severe conditions if the recent pattern in that area persists.
Corn condition continues to remain stable at levels that are marginally poor, but not terrible. Below trend is all but a guarantee, as I alluded to in the corn forecast we released last Friday, but significantly below trend does seem to be a low probability (though not impossible).
Figure 5. Percent of corn rated Excellent or Good minus the percent of corn rated Poor or Very Poor for Week 32 dating back to 1986 (red circles) and the final corn trend (blue diamonds). Data courtesy of USDA NASS.