Changing characteristics of precipitation for the contiguous United States

Using the US collection from the Global Historical Climatology Network Daily (GHCN-D) precipitation data for the contiguous United States (CONUS), this study examines the changing characteristics of precipitation during 1951–2013. In addition to mean precipitation, all precipitation events are divided into three categories: light, moderate, and heavy based on percentile thresholds. The historical trends are established for precipitation total, frequency and intensity, as well as for total and frequency of different intensity categories. Results show that from 1951 to 2013, mean precipitation increased at 1.66 % per decade, a higher rate than previous estimates. About one third of the increase is attributed to frequency change, whereas the other two thirds are attributed to an intensity increase. There was a slight decrease in light precipitation, a small increase in moderate precipitation, and much higher increase for heavy precipitation. Spatially, eastern and northern parts of the CONUS experienced higher rates of increase, whereas western regions experienced less increase. A statistically significant positive correlation exists between mean precipitation and precipitation change, suggesting the wet regions experienced more precipitation increase than dry regions. Seasonally, precipitation increased most for the fall, less in other seasons. Particularly, there were significant decreasing trends in summer precipitation for many parts of western and central CONUS. Regional frequency analysis is used to examine the change in extreme precipitation events with return intervals longer than a year. Results show that extreme precipitation events increased for most of the CONUS with the exception of the west region. These changes were a result of both a shift in the mean state and the shape of the precipitation data distribution.