Spatial extent of precipitation extremes in hydrology

Abstract

Precipitation extremes are a space-time phenomenon that influences many engineering design decisions. The occurrence of precipitation extremes is, however, rare and with values that can deviate notably from ”normal” observations. For design purposes, an estimate of areal rainfall depth for a corresponding return period is needed. Traditionally, point rainfall extreme value statistics are transferred to areal statistics using the concept of area reduction factors. These are, in general, based on simple assumptions without considering the effects of climate change. Area Depth Duration Frequency (ADDF) curves are a mathematical function relating the area of a location to the depth and frequency of a rainfall event for a certain temporal duration and return period. The calculation of the ADDF curves is, however, not straightforward, as, in contrast to point precipitation, areal precipitation is not measured but must be estimated. This work considers precipitation as a spatial phenomenon, without purely point statistics, and aims to assess areal precipitation extremes for the present and future time periods along their expected change with climate change.