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 20 July 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.
Figure 4. 1-month Evaporative Stress Index (ESI) from 23 July 2019. For additional information on the ESI, please refer to Anderson et al. (2012) and Otkin et al. (2013).
Narrative:
The soil moisture index (SMI) did drop across much of the Corn Belt, though not as much I had expected given the heat. Perhaps the unusually high dewpoints helped reduce soil water loss to evapotranspiration a bit. Other places, especially along the I-90 corridor, did receive substantial precipitation last week. Note that rainfall since last Saturday night is not reflected on this map, which explains the mildly negative SMI values across eastern Nebraska, for example. Overall the SMI (with the Noah-MP land surface model) is in good agreement with the latest Drought Monitor, though the recent dryness in parts of eastern Iowa and western Illinois isn’t being picked up as well with the standard Noah-MP simulation. The recent dry stretch in northern Indiana is being picked up well though and it’s close to being time to refer to that area as being in flash drought. As has been the case for the majority of the season, the dynamic vegetation simulation has been more aggressive with drying out the soils, with differences most substantial in the Great Plains and Corn Belt.
The 1-month ESI continues to show a lot of pockets of negative anomalies in the Corn Belt, which is likely a reflection of the combination of some or all of the following: the heat last week, recent dryness (where applicable), and the delayed development compared to normal. As I mentioned earlier, it will soon be time to start talking about the ‘D’ word in some places that were excessively wet earlier this season, IF decent precipitation doesn’t materialize soon.
Corn condition declined slightly last week but has remained pretty stable over the last month or so. As I have mentioned in recent weeks, the difference between the percent of corn in the Excellent-Good (EG) condition categories and Poor-Very Poor (PVP) condition categories is under 50 percent, which at this point in the season usually (though not always) indicates below trend corn yields should be expected.
Figure 5. Percent of corn rated Excellent or Good minus the percent of corn rated Poor or Very Poor for Week 29 dating back to 1986 (red circles) and the final corn trend (blue diamonds). Data courtesy of USDA NASS.