About this tool
This application allows the display and query of summer (July, August, and September) drought streamflow probabilities for Virginia streams. Maximum likelihood logistic regression is used to estimate drought probabilities 5 to 11 months in advance using streamflow data from the previous winter months.
Reading the symbology
Custom symbology was developed to display three summer month streamflow drought probabilities for each streamgage in the application (top, July; bottom-left, September; bottom-right August). The top circle (July) corresponds with the location of the physical streamgage and clicking on it displays site-specific streamgage and drought information.
Drought probability values are shown using a color coded scale of five probability classes and a sixth no-data class. The highest drought flow probability values from many Virginia equations range between 30% and 40%. A few equations have values approaching 100% drought flow probability. Only results from statistically significant relations are presented (p-value <= 0.05). Equations with p-values greater than 0.05 are identified as having no-data and are colored gray.