EXPLORING A HYPOTHETICAL CORRELATION BETWEEN DROUGHT AND LAKE AREA OF GROUNDWATER-FED LAKES IN THE NEBRASKA SANDHILLS

Lakes have often been used to help quantify the water resources within an area, but for many regions with numerous or ephemeral lakes, such as the Nebraska Sandhills, using ground-based methods is difficult. In many cases, use of Landsat imagery, discretized using the Modified Normalized Difference Water Index (MNDWI) and correlated to the Palmer Drought Severity Index (PDSI) has shown to be a promising approach. For example, this approach was used in the Prairie Pothole Region (PPR) in the northern Great Plains.

Over the study area, MNDWI was calculated using sixty-four biannual Landsat images covering the western lakes region of the Nebraska Sandhills. The resulting lake areas were then correlated to concurrent and six-month lag PDSI values, and using a linear regression between the current lake area and a predicted PDSI value a formula was found.

The formula is constrained by the temporal extent of the prediction, when it can be utilized; but it nevertheless can be used for predicting the water resources available during the next spring or fall. The methodology only took into account the lake areas during the spring and the fall due to the interference of ice, snow, and dense vegetation that can occur around the lakes during the other two seasons.

This method does not rely on ground-based lake measurements for the assessment of lake areas and has the flexibility to be adapted for the water resource assessment in other regions containing numerous permanent or ephemeral lakes, whose remoteness, numbers, or geological nature make traditional estimates costly or difficult.