Temporal and Spatial Variation in Rainfall at Marine Corps Base Camp Lejeune North Carolina Using Tipping Bucket Gauges

The Defense Coastal/Estuarine Research Program (DCERP) is a research-based program that is sited at Marine Corps Base Camp Lejeune (MCBCL), NC. This program provides a unique opportunity to create results of broadly scoped ecological research, that improve our understanding of the structure and function of diverse coastal ecosystems, while directly integrating this research to address the Base’s management needs for sustaining the military training mission. This presentation outlines current efforts to assess the temporal and spatial trends in rainfall amounts to aquatic and terrestrial ecosystems within the confines of MCBCL (~ 60,700 ha) using tipping bucket gauges (HOBO Data Logging Rain Gauge, Onset Computer Corp.). To date, 23 tipping bucket gauges have been deployed, each with their own battery operated data logger. The data loggers record the time and date for each 0.2 mm of rainfall collected, allowing delineation of rainfall amounts within and between events. Five manual rain gauges with wind screens (Model 260-2510 Standard Rain Gauge, NovaLynx Corp.) are co-located with tipping buckets across MCBCL in order to assess accuracy. Rainfall amounts on an event basis are highly linearly correlated between the tipping bucket gauges and the manual rain gauges with a slope of 0.84 +/- 0.09 (95% confidence level), suggesting a consistent ~16% negative bias using the tipping bucket gauges. Measured rainfall amounts are more variable during the warm months of the year (% coefficient of variation (CV) > 25) than during the fall and winter months (%CV < 15). Analysis using repeated measures indicates date not location is driving the observed differences, suggesting that proximity to the Atlantic Ocean along the southern boundary of MCBCL is not influencing rainfall patterns across the Base. When averaged over time periods of at least 6 months, however, the uncertainty in rainfall amount is only 13% CV, providing an estimate of uncertainty for historical rainfall records at MCBCL that are based on single point observations. Interpolated maps of rainfall deposition are being generated using thin plate spline interpolation in conjunction with semi-variograms to measure spatial autocorrelation between collectors. The resulting maps will form the basis of estimating nutrient inputs from rainfall into different aquatic and terrestrial ecosystems at MCBCL.