Comparison of Extreme Rainfall Frequency in Lubbock, Texas using Gauge and Radar Data

Precipitation return periods are used for a variety of city planning purposes – wastewater infrastructure and floodplain management in particular. An accurate estimate of extreme precipitation frequency is important when determining how much money to allocate for dealing with these often disruptive events. Due to the localized nature of thunderstorm precipitation in the West Texas region, extreme precipitation events that occur within Lubbock County often are not recorded by the Automated Surface Observing System (ASOS) rain gauge located at Lubbock International Airport despite causing significant effects within the City of Lubbock. As a result, it is possible that the airport rain gauge data does not provide a complete picture of the actual frequency of extreme rain events in the City of Lubbock. In this study, an analysis of the 10-, 50-, and 100-year return period for daily precipitation amounts will be completed using two data sources, the traditional rain gauge data approach and WSR-88D data, which has better spatial resolution. It is anticipated that using radar data to determine the extreme rainfall return periods will provide a more accurate picture of the extreme rainfall climatology for the region.

Archived rain gauge data from the Lubbock International Airport from the National Climatic Data Center (NCDC) will be used to compute the 10-, 50-, and 100-year daily rain events using a peak-over-threshold technique for fitting extreme value distributions. The peak-over-threshold technique was chosen in favor of the generalized extreme value distribution method because it incorporates multiple extreme events within a single year while the latter uses only the largest extreme event in a given year. It is anticipated that more than one extreme rainfall event will have occurred in a given year. The second step of the analysis will be to evaluate peak daily rainrates using archived WSR-88D data from the NCDC. 1-hour precipitation estimates based on the KLBB (Lubbock, TX) radar site will be used to compute 24-hour radar-estimated rain totals which exceed the 10-, 50-, and 100-year return period daily rain totals found using the gauge data. The frequency of the radar estimated extreme rain events will be compared with the events found in the ASOS rain gauge data to see whether using a single weather station underestimates the frequency of extreme rain events in the Lubbock area.

In addition to the comparison between the gauge and radar data return period information, a trend analysis will be completed to assess whether a long-term increase or decrease in extreme rainfall events is occurring in the region.