The pattern of soil moisture across the state of Alabama and more broadly the Southeastern United States has evolved into one of marked disparity over relatively short distances (see Fig. 1d) and time frames. The SPoRT Center manages its own instance of the NASA Land Information System (i.e., “SPoRT-LIS”), which produces real-time soil moisture estimates in an observations-driven modeling framework. Hourly and daily output fields are available on the SPoRT Center web page, and 3-hourly and daily data are delivered to select NOAA/NWS weather forecast offices for enhanced decision support in areas such as drought and hydrologic applications.
In general, 2019 has been quite a wet year across large portions of the U.S., with parts of Alabama being no exception (especially northwestern Alabama). Beginning in May, a rapid deterioration in soil wetness occurred across many parts of the Southeast due to unusually hot and dry conditions during the last half of May through early June. However, the latter part of June into July featured well above-average rainfall in some areas that reversed the rapid drying trends, especially over far northwestern Alabama, Mississippi, and western Tennessee. The variations in SPoRT-LIS total-column soil moisture percentiles over the past 4 months are given in Fig. 1, illustrating the regional spatiotemporal trends described above from April through July.
Interestingly, the soil moisture percentiles across far northern Alabama diminish quite substantially from west to east by the end of July (Fig. 1d), approaching the 98th percentile in western Lauderdale county (NW Alabama) to less than the 10th percentile across Jackson county (NE Alabama; counties of northern Alabama shown in Fig. 2). The current conditions on 31 July 2019 relative to the 31 July historical soil moisture distributions from a 1981-2013 SPoRT-LIS daily climatology further illustrate this sharp zonal contrast in soil wetness anomalies within the county-based histograms of Fig. 3. The county-mean 0-2 meter relative soil moisture on 31 July 2019 in Lauderdale county is at the 87th percentile compared to the 33-year historical distribution of 31 July values (Fig. 3a). Meanwhile, Limestone county to its east has a mean soil moisture at the 61st percentile (Fig. 3b), followed by the 51st percentile in Madison county (Fig. 3c) and only the 24th percentile in Jackson County, AL. These results serve to illustrate the highly variable nature of rainfall and resulting soil wetness and agricultural impacts that can occur across the Southeastern U.S. during the summer months.
Finally, despite the month-to-month swings in soil moisture anomalies across much of the Southeast in recent months, one corridor that has persistently experienced abnormally dry conditions extends from southeastern Alabama into southern and central Georgia and western South Carolina. In fact, since 31 May (Figs. 1b-d), southeastern Alabama has seen soil moisture percentiles less than 20%, analogous to moderate to severe (or worse) proxy drought categories based on community-accepted conventions of percentile anomalies. These dry regional pockets in the SPoRT-LIS analysis strongly correspond to the most recent U.S. Drought Monitor weekly product, issued on 30 July (Fig. 4).