A Statistical Methodology to Discover Precipitation Microclimates in Southeast Louisiana: Implications for Coastal Watersheds

Abstract

This study quantifies the spatial distribution of precipitation patterns on an annual basis for southeast Louisiana. To compile a long-term record of 24-h rainfall, rainfall reports collected by National Weather Service (NWS) cooperative observers were gathered from National Climatic Data Center (NCDC) archives, private collections of observational data held at regional and local libraries, NWS offices, and local utility providers. The reports were placed into a digital database in which each station?s record was subjected to an extensive quality control process. This process produced a database of daily rainfall reports for 59 south Louisiana stations for the period 1836?2002, with extensive documentation for each site outlining the differences between the study?s data and the data available from the NCDC Web page. A statistical methodology was developed to determine if the four NCDC climate divisions for southeast Louisiana accurately depict average monthly rainfall for the area. This method employs cluster analysis, using Euclidean distance as the measure of dissimilarity for the clustering technique. To resolve missing rainfall observations, an imputation scheme was developed that uses the two most similar stations (based on Euclidean distance) to determine appropriate values for missing rainfall observations. Results from this testing structure show statistical evidence of precipitation microclimates across south Louisiana at higher spatial scales than those of the NCDC climate zones. Quantifying the spatial extent of daily precipitation and documenting historical trends of precipitation provides critical design information for regional infrastructure within this highly vulnerable area of the central Gulf Coast region.