A study of heavy rainstorms Over North Bengal

Abstract

A detailed study of all the heavy rainstorms over North Bengal has been made with a view to finding out whether the rainstorm of October 1968, believed to be unprecedented, has actually contributed the suggesting this study highest depths of precipitation over this area. In all, 85 heavy rainstorms have been selected during the period 1901-1968 and analysed by isohyetal method.

Depth-duration curves have been drawn for rainstorms of2-day and of1onger durations and the enveloping curve has been obtained. Depth-area-duration curves for very heavy rainstorms, considered important for any design work in river valley projects, have also been drawn, It has been revealed that the rainstorm of 11-13 June 1950 has contributed the highest depths of precipitation for 1-day to 3-day durations over the area under study during the period.

Synoptic situations associated with June 1950 and October 1968 rainstorms along with those of other comparable rainstorms have been described. The coefficient of variability of Rainfall for each of the months May to October and for annual rainfall have been computed in respect of 17 stations of North Bengal.

Probable maximum depths of precipitation in one day have been obtained by duration-curve method. A regression equation has also been formul8;ted for obtaining average depths of precipitation over North Bengal  from rainfall data of three selected stations.