The proper monitoring of drought conditions takes into account deficits of rainfall, and subsequent impacts to soil moisture and the hydrologic system. Streamflows and groundwater may suffer from lack of adequate supply for ecological or recreational purposes, for example. While lack of soil moisture will most often have potential impacts for agriculture. Demands on soil moisture by crops and vegetation obviously decrease during the winter, especially in northern Alabama where relatively cold soil temperatures inhibit growth. However, in southern portions of the state, the growing season may last through much of the winter.
To help monitor changes in soil moisture, the LIS now contains an extra output field, Integrated relative soil moisture difference, which is listed as RSOIMDIFF on the LIS web page for Alabama…
These plots represent one-week changes in column-integrated (0-200cm) relative soil moisture. One week differences were chosen because of adequte responses in soil moisture on these timescales and also to facilitate feedback to the U.S. Drought Monitor, which takes place on a weekly basis. Notice the latest image produced this morning, indicating the recent rainfall and subsequent moisture changes in northern Alabama.
Notice the swath of increased soil moisture across NW Alabama, where rainfall fell over the past day. Very little to no rainfall fell in remaining areas indicated by the yellow colors (urban areas show up as the dark orange coloring). Soil moisture changes will be reflective of rainfall amounts, particularly this time of year when evapotranspiration rates are low. However, there will still be differences, owing to soil moisture and vegetation types, temperature inputs and various other parameters. Otherwise, a simple rainfall map of rainfall would be sufficient to determine soil moisture changes. A plot of the Stage-IV rainfall over the last week is included below (Figure 2).
What is going to be really interesting is to watch the changes in soil moisture during the upcoming spring and summer, to see how larger differences in heat and moisture fluxes, precipitation, and vegetation types result in soil moisture changes.