Impact of Precipitation Organization on River Discharge Across North Carolina

Abstract:

This study builds from an existing four-year NEXRAD radar-based precipitation climatology over the southeastern U.S. to examine the hydrological response of river systems in North Carolina to different modes of precipitation organization in a Geographic Information Systems (GIS) framework. The climatology uses a simple two-category framework of precipitation organization based on instantaneous precipitating feature size: mesoscale precipitation features (MPF) and isolated precipitation. Specifically, the following questions are addressed: First, what are the discharge response characteristics to seasonal changes in precipitation in different watersheds across North Carolina, from the mountains to the coastal plain? Second, how does precipitation organization, whether long-lasting mesoscale systems or short duration isolated convection, affect these watershed characteristics? This analysis defines five watersheds in North Carolina based on five North Carolina river basins using GIS watershed delineation techniques. It was found that lag time between maximum precipitation and maximum discharge increased from 1-2 days in the western mountainous watersheds to 7-8 days in the eastern coastal plain watersheds. The steeper and more impervious western watersheds promoted more rapid discharge of precipitation, while the flat and swampy eastern watersheds drained more slowly. Precipitation originating from MPF events produced stronger precipitation-discharge correlations in the winter and fall than in the summer and spring, while most isolated precipitation-discharge correlations were relatively weak. Overall, it was found that MPF precipitation is the main mode of precipitation organization that drives daily watershed discharge, and differences in watershed precipitation-discharge lag times can be best explained by the watershed characteristics rather than differences in precipitation organization.