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) will also be included in our analysis once data for all of the U.S. are available later this season. 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 1 June 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.
Precipitation has been very spatially inequitable over the eastern 2/3 of the U.S. during the past few months in general and the last few weeks in particular, with the Great Plains and Corn Belt regions receiving excessive precipitation and inadequate over the southeastern U.S. There is good agreement between the standard Noah-MP simulation and dynamic vegetation simulation about the level of excess or deficit of root zone soil moisture in both of these regions. The only area where this isn’t good agreement between simulations is across central and southern Texas where the dynamic vegetation simulation shows more negative values than the standard Noah-MP simulation.
The latest U.S. Drought Monitor shows that while the amount of drought in the U.S. is very low, there has been expansion of abnormal dryness and drought over the southeastern U.S., where the SMI values are strongly negative. A pocket of negative SMI values still exists in northern North Dakota, though this hasn’t gotten much worse over the past few weeks. Planting progress remains well behind schedule in the Corn Belt States and much of the region has received additional, unneeded rain since last Saturday (the data cutoff for this map), though in general, it has been less than the previous few weeks. Conditions also remain very wet in the prime wheat region of Kansas and Oklahoma, which seems to be taking a toll on condition of winter wheat in that area.