An Update to Probable Maximum Precipitation Accounting for More Than Moisture Availability Alone: A Case Study of Nepal.

The moisture maximization approach, the most common technique for estimating Probable Maximum Precipitation (PMP), assumes that the upper limit of extreme precipitation can be estimated by maximizing atmospheric moisture availability alone. However, several atmospheric variables often play a role in the occurrence of extreme precipitation. In this paper, a generalization is proposed to incorporate other relevant atmospheric variables with a two-step multifactor maximization approach. In the first step, the dominant atmospheric variables are screened. In the second step, the maximization ratio for each variable is calculated separately and then combined as a weighted average to obtain a combined maximization ratio. When applied to a case study in Nepal, the multifactor maximization approach results in PMP estimates substantially different (up to 4x) from the conventional moisture maximization approach in regions where the PMP is particularly sensitive to factors other than atmospheric moisture availability.