Estimation of probable maximum precipitation for a 2-day duration: Part 2 — north Indian region

Summary

In a previous study the authors have estimated the probable maximum precipitation (PMP) for a 2-day duration using Hershfield's formulaX _PMP =X _n +k _m σ _n for stations in the southern Indian region. In this paper, the study is extended to estimate the PMP for stations in the north Indian region, north of 20°N. Maximum annual 2-day rainfall data for an 80-year period, from 1901, were obtained for 286 stations in the region. A mathematical relationship between the frequency factor (k _m ) and the mean annual extreme rainfall (X _n ) was developed to bek _m = 18.15 exp (−0.0448X _n ). This equation was used to obtaink _m for different values ofX _n and, subsequently, to estimate 2-day PMP values for the 286 stations. Using these PMP estimates, a generalised chart was prepared, showing the spatial distribution of 2-day PMP. It was found that 2-day PMP over the north Indian region varied from 60 cm to 130 cm, and the average ratio of the 2-day PMP to the highest observed 2-day rainfall was found to be 1.91. The results show that there have been instances when almost 2-day point PMP have occurred at some of the stations in the region. These results indicate that the statistically estimated PMP rainall are not therefore, mere theoretical estimates, but they can occur under optimum meteorological conditions.