A PRECIPITATION ORGANIZATION CLIMATOLOGY FOR NORTH CAROLINA : DEVELOPMENT AND GIS-BASED ANALYSIS

Abstract

A climatology of precipitation organization is developed for the Southeast United States and is analyzed in a GIS framework. This climatology is created using four years (2009-2012) of daily-averaged data from the NOAA high-resolution multi-sensor precipitation estimation (MPE) dataset, specifically the radar-based quantitative precipitation estimation (QPE) product and the mosaic reflectivity. The analysis associates precipitation at each pixel with the spatial scale of precipitation organization, either a mesoscale precipitation feature (MPF) or isolated storm. While the long-term averaged precipitation totals of these systems may be similar, their hydrological and climatological impacts are very different, especially at a local scale. The classification of these modes of precipitation organization in the current precipitation climatology provides information beyond standard precipitation climatologies that will benefit a range of hydrological and climatological applications. This study focuses on North Carolina and takes advantage of a GIS framework to examine hydrological responses to different modes of precipitation organization. Specifically, the following questions are addressed: First, what are the discharge response characteristics to precipitation events in different watersheds across the state, from the mountains to the coastal plain? Second, what are the different impacts on watershed discharge between MPF precipitation and isolated precipitation? We first present seasonal and annual composites of precipitation and duration of MPF and isolated storms across three regions of North Carolina: the western mountains, the central Piedmont, and the eastern coastal plain. Further analysis in a GIS framework provides information about the impacts this seasonal and geographic variability in precipitation has on watershed discharge. This analysis defines five watersheds in North Carolina based on five North Carolina river basins using ArcGIS watershed delineation techniques. The amount of precipitation that comes from MPF and isolated convection in each watershed is estimated using ArcGIS and QPE data from a climatology of precipitation organization. Comparing these estimates to USGS streamflow data provides information about the impact different modes of precipitation organization have on watershed discharge in North Carolina. It was found that precipitation from MPF and isolated events had substantial spatial and temporal variability. While MPF average daily precipitation was greatest in the winter, isolated average daily precipitation was greatest in the summer. This resulted in seasonal and spatial variations in precipitation-discharge correlations. 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. Additionally, the watersheds in the western mountains experienced stronger correlations with a shorter time lag than coastal watersheds. It was determined that much of this spatial variability in precipitation-discharge correlations could be explained by watershed characteristics. 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.