ESTIMATION OF PROBABLE MAXIMUM PRECIPITATION FOR A 2-DAY DURATION .2.NORTH INDIAN REGION

In a previous study the authors have estimated the probable maximum pr ecipitation (PMP) for a 2-day duration using Hershfield's formula X(PM P) = X(n)BAR + k(m)sigma(n) for stations in the southern Indian region . In this paper, the study is extended to estimate the PMP for station s in the north Indian region, north of 20-degrees-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 fr equency factor (k(m)) and the mean annual extreme rainfall (X(n)BAR) w as developed to be k(m) = 18.15 exp (- 0.0448 X(n)BAR). This equation was used to obtain k(m) for different values of X(n)BAR and, subsequen tly, to estimate 2-day PMP values for the 286 stations. Using these PM P estimates, a generalised chart was prepared, showing the spatial dis tribution of 2-day PMP. It was found that 2-day PMP over the north Ind ian region varied from 60cm to 130cm, and the average ratio of the 2-d ay PMP to the highest observed 2-day rainfall was found to be 1.91. Th e 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 therefo re, mere theoretical estimates, but they can occur under optimum meteo rological conditions.