Estimation of Probable Maximum Precipitation in the context of climate change

Probable Maximum Precipitation (PMP) is the maximum depth of precipitation at a location for a given duration that is meteorologically possible. It is a crucial information for any water infrastructure, such as dams, culverts, drainage network in order to ensure a desirable probability of exceedance. This paper proposes a technique for estimation of PMP, suitable in the context of climate change. Out of several available methods, Hershfield method is considered as a convenient and effective statistical method of PMP estimation, provided sufficiently long precipitation records are available. The most crucial step in Hershfield method is the precise estimation of frequency factor (K) and its enveloping technique. There is no universally accepted enveloping technique of K. Different values of K and different types of enveloping techniques have been suggested and used by various investigators across the world. We introduce an upgradation in the existing enveloping technique in order to bring clarity and universality in the estimation, particularly in the context of climate change. This updated enveloping technique and the conventional Hershfield method-both are applied to develop PMP maps for the entire Indian mainland over the past century (1901-2000). Comparison between the proposed and existing methods of PMP estimation reveals a better estimation of spatio-temporal variation of PMP, avoiding unusual overestimation of PMP in the low rainfall extreme regions of India by existing Hershfield method. In brief, the contributions of this paper are as follows: • An upgradation of the existing Hershfield Method [1] by introducing a new enveloping technique for the frequency factor (K). • The single envelope curve in the existing Hershfield method is modified as a composite curve, consisting of a straight-line portion and an exponentially decaying portion. • Development of PMP maps over India using both Hershfield method and the proposed technique.