Contribution of daily contiguous rainfall areas to warm season precipitation in the north central United States

Increases in damage associated with floods in the North Central U.S. call for a better understanding of the precipitation events that lead to these floods. Analysis of long records of historical observations of regional precipitation provides an opportunity to document both the basic characteristics and trends in temporal and spatial precipitation characteristics. Previous studies with this goal have used relatively short time scales, station data with coarse, non-uniform resolution with no regard to the spatial patterns or correlation among stations. I use a dataset developed as input to the Variable Infiltration Capacity (VIC) hydrologic model (Liang et al., 1994, 1996) by Maurer et al. (2002) which uses both horizontal interpolation and elevation corrections. This produces a 1/8° grid of daily precipitation from 1950 through 2010 over the entire coterminous United States (CONUS). The North American Regional Reanalysis (NARR) reported by the National Center for Environmental Prediction (NCEP) will also be used to analyze specific meteorological variables that are not available in the VIC dataset. A procedure called the method for object-based diagnostic evaluation (MODE) will allow me to identify precipitation events of certain contiguous size and rainfall depth. Research performed for completion of this thesis has led me to the following findings: 1) 90th percentile precipitation events, while not characterized as extreme, actually contribute 50-70% of the total warm season precipitation events in the North Central United States. 2) A 90th percentile event, depending on the location within the region of interest, is either ¼” or &half” of total daily precipitation. 3) 90th percentile events have increased from the first to the second half of the past 61 years. 4) The main environmental indicators of these rainfall events are Convective Available Potential Energy (CAPE) and water vapor flux convergence, which provide insight into the characteristics of warm season precipitation in the region. 5) These 90th percentile events are quite common and can happen many times per month during the warm season. 6) These events, more often than not, occur in a series on consecutive days within a narrow corridor rather than as an isolated event which can lead to potential flooding problems