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 21 September 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 September 2019. For additional information on the ESI, please refer to Anderson et al. (2012) and Otkin et al. (2013).
Narrative:
The abnormal to near-record warmth continued for much of the eastern 2/3 of the country last week. In the southeastern U.S. this combined with a near total lack of precipitation has led to flash drought being imminent (e.g., Mississippi) or in the beginning stages. It should be noted that the dynamic vegetation simulation (Fig. 2) has been much more aggressive with the rapid drying in this area and I would say that the truth may well be closer to the dynamic vegetation simulation than the standard Noah-MP simulation (Fig. 1). The simulations presented here do not contain assimilation of any satellite derived observations but I would be curious to see what anomalies look like with assimilation of soil moisture (e.g., SMAP) or a leaf area index (LAI). I’ll finish off the section on the southeast by showing a forecast of top soil moisture from NASA-SPoRT that was put out yesterday on Twitter (Fig. 5).
The rest of the eastern U.S. has also been dry in September, with much of Appalachian, Middle Atlantic, and New England regions in abnormal dryness or moderate drought on the U.S. Drought Monitor. This is in good agreement with the SMI maps and the ESI map (Fig. 4).
There were still pockets of dryness or moderate drought across the Corn Belt at the end of last week (e.g, eastern Nebraska, central Illinois, north Indiana), though much of this will be eradicated on next week’s map given the rains that fell last weekend and are expected this weekend. If anything, I would be more concerned about flash flooding next week in places where the SMI is decently positive as rainfall in excess of 4 inches is probable from far eastern Nebraska into Illinois. This also is not good for crops needing drier weather as we head into October. May not change yield prospects a lot but it will certainly delay any harvesting that is currently planned for the first week to ten days of October.
Further to the north, much of the upper Midwest and Northern Plains remain wet and extreme moist anomalies persist across South Dakota. It appears the heaviest precipitation will remain to the southeast but any additional rainfall here isn’t welcome at this time.
Figure. 5. Forecast top-soil moisture percentiles from NASA-SPoRT valid for Friday, 4 October.