Thursday, 13 January 2005: 3:30 PM
Discovery of Annual and Seasonal Precipitation Micro-Climates within South Louisiana: Impacts for Coastal Management
Understanding precipitation cycles and their impacts on ecosystems is critical to coastal and estuary management projects. The plight of south Louisiana coastal lands and the health of her marine ecosystems has been widely publicized with at least 40 million dollars a year since 1991 going to coastal restoration activities from the federal Coastal Wetlands Planning, Protection, and Restoration Act (CWPPRA) more commonly known as the Breaux Act. Federal and Louisiana officials estimate an additional 14 billion dollars will be needed to fully implement the strategies outlined by the Coast 2050 publication to restore the central Gulf ecosystems. Fundamental to these efforts is an understanding of historical rainfall patterns, particularly their spatial characteristics and the historical trends of drought and flood cycles. To investigate annual and seasonal patterns of precipitation, statistical analysis was performed on a dataset of daily rainfall observed at 63 south Louisiana stations from 1836 to 2002. Each station record was examined for data quality and continuity with special attention to time periods surrounding station relocation or equipment exchange. Mean Areal Precipitation (MAP) sheets were compiled for every month from 1836 to 2002 to document the daily rainfall across south Louisiana and neighboring portions of southern and coastal Mississippi. Using these MAP sheets, missing data was examined to see if a reasonable value could be substituted to extend the continuity of a stationís rainfall record. With data quality and continuity checks completed, a series of statistical tests were conducted to determine an accurate scheme to form station groups. To group stations together, each station was required to have a normal distribution of monthly average rainfall, a statistically equivalent variance, and a statistically equivalent mean when compared with other stations in the group. As a result of the Shapiro-Wilk Test, the F-Test, and the Student T-test, eight station groups were formed within the study region of south Louisiana. To define seasonal rainfall patterns across the study region, statistical tests were conducted for twelve, six, and three month intervals. For the six month intervals, group rainfall averages and pooled variances were calculated for each interval beginning with January-July and ending with December-May. For the three month intervals, group rainfall averages and pooled variances were calculated for January-March and concluded with December-February. To test the hypothesis of a statistically significant difference in mean rainfall between the eight groups for a twelve, six, and three month intervals, the Student T-test was conducted. The results obtained from this test show statistical evidence of annual and seasonal precipitation micro-climates across south Louisiana existing on spatial scales smaller than the climate regions defined by NOAA climate publications. The development of these historical rainfall statistics should improve the accuracy of the data provided to coastal zone hydrologic models resulting in improved simulations of groundwater flow and river discharge for coastal restoration projects.