RAINFALL CHARACTERISTICS AND SPATIAL CORRELATION FOR THE GEORGIA COASTAL PLAIN

The Georgia Coastal Plain of the United States holds significant agricultural and hydrologic importance. The profitability and sustainability of agriculture in this and other regions are dependent upon climatic patterns and, in particular, rainfall. The temporal and spatial variability of this rainfall play key roles in agricultural management. Developing an understanding of seasonal patterns and individual storm characteristics is critical. Thirty years of rainfall data collected from a dense rain gage network on the 334 km2 Little River Watershed near Tifton, Georgia, were analyzed for this purpose. Storm patterns were characterized by season to establish means and trends. Individual storm characteristics and spatial correlation patterns within storms were quantified. Rainfall patterns, although highly variable from year to year, show rainfall to be greatest in the midsummer months with high intensity, convective thunderstorms. While these summer storms yield relatively low rainfall depths, they occur more frequently than during other seasons. Frontal storms with moderate rainfall amounts are typical of the winter and spring months. The fall months generally have low rainfall totals and storms during this time occur less frequently than during the other months. For larger storm events, defined here as those where at least one rain gage in the network measured 25.4 mm or greater during the event, the mean storm depth weighted over the mean storm coverage of 295 km2 was 20.6 mm, while the mean storm duration was 7.2 h. For these larger events, the summer storms are separated by the least time between events (mean of 116 h) while the fall events are separated by the greatest time (mean of 291 h). For summer events, rain gage depths for individual storm events collected by gages separated by 1.9 km or less are likely to be highly correlated (r iÝ 0.9). This distance increases to 9.2 km for the winter. High correlations (r iÝ 0.9) are expected up to distances of 5 km throughout most of the year, except summer. This analysis establishes the basis for detailed modeling across this and other watersheds in the region.