Precipitation Intensity-Duration-Frequency Functions for the Bannu Region NWFP Pakistan (RESEARCH NOTE)

Abstract

The function of precipitation intensity-duration-frequency is needed for the planning and design of water resource projects. Short duration precipitation data are hardly available. However the total hourly-recorded available precipitation data for different parts of NWFP from different departments have been collected and analyzed for the present study. The data from WAPDA is found to be more authentic. Making use of the data, functions of intensity-duration-frequency for precipitation are developed for the Bannu region, representing the lower hilly and plane areas in NWFP. The IDF curves are plotted for 2, 5, 10, 25, 50 and 100-year return periods. The theoretical intensities of precipitation calculated by the developed functions are in close agreement with those recorded at the stations through automatic gages. Only 7 % variation is observed for most of the time. The values of the constants k, b and exponents n, m in the IDF function are calculated from the observed precipitation data. The correctness of the developed function is ascertained through its comparison with existing equations for depth duration developed for the world’s largest rainfall events. The function developed is found to produce more realistic results for regions in NWFP. The developed function may be used in the same region in a radius of about 100 km. For design practices regarding the prediction of precipitation in the future, instead of consulting 26 years of data available for the same region on hourly basis.