The hydro‐meteorological estimation of probable maximum precipitation under varying scenarios in Sri Lanka

Abstract

Probable maximum precipitation (PMP) is widely used as an input in rainfall-runoff modelling to estimate probable maximum flood (PMF), which is required for the design of spillways of large dams. In relation to dam safety studies at 32 dam sites, an analysis was done of extreme rainfalls in Sri Lanka, which is influenced by the Asian monsoon system and cyclonic effects. Accordingly, the Hershfield's statistical method, which is one of the recommended procedures of the World Meteorological Organization (WMO), was used for estimating PMP. It is also a technique that can be readily used in design office practice. However, it is of significant value and scientific interest to explore what the outcome would have been if the physically based hydro-meteorological procedure had been adopted. For this purpose, long series of annual maximum daily rainfall data from seven stations were analysed. The research shows that the maximum moisture and corresponding wind run or the use of maximum moisture alone are two scenarios, which yield results compatible with the statistical PMP. Although globally there is a tendency to exclude wind maximization, this does not automatically apply to a country like Sri Lanka, which experiences cyclonic rainfall and special attention should be paid to precipitation efficiency. These results are further confirmed by a frequency analysis based on the generalized extreme value (GEV) distribution. An approximate value of PMP could be in the order of 2.0-3.0 times the maximum observed daily rainfall. However, this aspect needs further investigation when observed maxima are near PMP storms.

Effects of climate change on probable maximum precipitation: A sensitivity study over the Alabama‐Coosa‐Tallapoosa River Basin

“…Probable maximum precipitation (PMP) is defined as “ the greatest depth of precipitation for a given duration meteorologically possible for a design watershed or a given storm area at a particular location at a particular time of year ” [ World Meteorological Organization , ], and it represents the largest rainfall that could physically occur under a series of adverse atmospheric conditions [ Casas et al ., , ; Douglas and Barros , ; Schreiner and Riedel , ; Fernando and Wickramasuriya , ]. Distinguished from the statistically based T ‐year extreme rainfall estimate that associates depth with annual exceedance probability (AEP = 1/ T ) [see Kao and Ganguly , ], PMP is the deterministic upper bound of extreme storms.…”

PMP and PMF estimations in sparsely-gauged Andean basins and climate change projections

“…Therefore, this factor is not taken into consideration, which reduces the methodology to equation (4), where the maximization is determined only by the moisture factor, as explained in Section 2.5.2. As a consequence of this assumption, lower PMP estimations are obtained, as Fernando and Wickramasuriya (2010) concluded.…”

“…Table 2 indicates that the HM2 method gives PMP values 35% smaller than the HM1 method for the BL period; this could change if we also included the amplification by a wind factor in order to evaluate more possibilities, as proposed by Fernando and Wickramasuriya (2010). These authors conclude that the double-maximized HM2 method is similar to Hershfield's PMP estimation.…”

An improved moisture and wind maximization method for probable maximum precipitation estimation and its application to a small catchment in China

“…The conventional moisture maximization method involves only the moisture factor (e.g., moisture content or precipitable water) (Chavan and Srinivas, ). Wind, as a typical dynamic factor with easy access, is combined with the moisture maximization method to develop the MWM approach (Fernando and Wickramasuriya, ; Boota et al ., ). The MWM approach involves maximizing wind and moisture conditions that affect the occurrence of rainstorms, the moisture and wind maximization factor (MWMF) is expressed by Equation , but before use, surface dew point data corresponding to observed storms should be collected for precipitable water calculation (Fernando and Wickramasuriya, ; Boota et al ., ). where W d is the precipitable water corresponding to the 12‐hr persistent dew point, mm; W m is the maximum precipitable water corresponding to the highest dew point within the study duration, mm; V d is the average 12‐hr persistent wind speed for the observed storm, m/s; and V m is the maximum average observed wind speed within the study duration, m/s.…”