Probable Maximum Precipitation Study for New Jersey : Final Report

Abstract

The Study provides Probable Maximum Precipitation (PMP) depths for all drainage basins within New Jersey and those with contributory areas in adjacent states that drain into NJ. PMP depths provided in the Study supersede the current Hydrometeorological Reports (HMRs) PMP depths from HMR 51 (Schreiner and Riedel, 1978) and HMR 52 (Hansen et al., 1982). These prior reports by the National Weather Service do not incorporate significant storm events that have occurred over the last 40 years. The Study incorporates these events and reflects the most current practices used for defining PMP, including comprehensive storm analyses procedures and an improved understanding of the weather related to extreme rainfall throughout the region.

PMP is a deterministic estimate of the theoretical maximum depth of precipitation that can occur over a specified area and is used to compute the Probable Maximum Flood (PMF). Parameters to estimate PMP were developed following the storm-based approach as discussed in the HMRs and subsequently refined in the numerous site-specific, statewide, and regional PMP studies completed since the early 1990s.

Methods used to derive PMP values for this Study included consideration of numerous extreme rainfall events that have been appropriately adjusted to each grid point and represent each storm type (Local, General, and Tropical). The large number of storm events provides enough data from which to derive the PMP. The process of combining maximized storm events by storm type into a hypothetical PMP design storm results in a reliable PMP estimation by combining the worst-case combination of meteorological factors in a physically possible manner.