Revised Rainfall Frequency Analysis for Houston

A statistical analysis of rainfall data for four Houston area stations is presented. A similar analysis was performed on the same stations in 1961 by the U.S. Weather Bureau. Both methods used the Gumbel Type I distribution to predict design storms for particular durations (1 hr. to 24 hrs.) and for particular return periods (2 to 100 yrs.). A Comparison of the design storms calculated in each of the studies identified rainfall rate changes which have occurred over the past two decades. The largest changes found were associated with the 24 hr. event. The downtown station recorded a 13 decrease in the 24 hr. 100-yr. storm over the past 20 years, while Conroe, Galveston, and Hobby stations (outside of Houston) recorded an increase of 15 percent for the same storm. These changes can be linked to the heavy urban development in the Downtown area, and to changing climatic patterns along the Gulf Coast. Drainage designs for the affected areas should be adjusted upward to account for these changes.