Changing patterns of daily precipitation totals at the Coweeta Hydrologic Laboratory, North Carolina, USA
A pattern of increasing frequency and intensity of heavy rainfall over land has been documented for several temperate regions and is associated with climate change. This study examines the changing patterns of daily precipitation at the Coweeta Hydrologic Laboratory, North Carolina, USA, since 1937 for four rain gauges across a range of elevations. We analyse seasonal total rainfall, number of rain days and the frequency of heavy rainfall. We compare these with several teleconnections, including the Bermuda High Index (BHI), the West BHI, the North Atlantic Oscillation (NAO) and the El Niño-Southern Oscillation. Our data show a tendency for increased variability, including major periods of drought, with fewer rain days recently, especially in summer. Only autumn tended to have increases in rainfall frequency and magnitude; this is the season when orographic enhancement is at its strongest. The major driver of precipitation at Coweeta is the strength of the Bermuda High. The strength of the NAO is important in summer. The results are relevant to the southeast United States in general, given that the region comes under the influence of similar air masses during the year. The findings are applicable to the wider Appalachian Mountains and to other mountainous regions where there is significant orographic enhancement.