Abstract
AbstractDetermining the impact of catchment flooding requires an estimate of extreme spatial rainfall intensity. Current flood design practice typically converts a point estimate of rainfall intensity into a spatial rainfall intensity using an areal reduction factor, assumed constant across an entire region. Areal reduction factors do not explicitly consider regional variations in extreme rainfall. Here, a new approach for spatial estimates of extreme rainfall is introduced that directly incorporates the spatial area (A) into an intensity-frequency-duration relationship (IFD). This IFDA approach uses spatial rainfall fields to overcome shortcomings of the areal reduction factor by explicitly incorporating spatial variations in the extreme rainfall intensity. The IFDA approach is evaluated for 11 case study regions in Australia, across climates (tropical to Mediterranean), areas (25–7,225 km2), durations (1–4 days), and average recurrence intervals (ARI 2–100 years). The change in extreme spatial rainfall...
Highlights
Of all natural disasters, floods have the highest global cost and affect the most people (Kousky and Walls 2014; Miller et al 2008; Strömberg 2007)
It is this spatial variation in intensity-frequencyduration area (IFDA) that produces the different IFDA curve behaviors exhibited in Figs. 3(a and b)
An IFDA, which is calculated directly from spatial rainfall fields, adds the extra dimension of area to an IFD curve to account for spatial variation over a catchment
Summary
Floods have the highest global cost and affect the most people (Kousky and Walls 2014; Miller et al 2008; Strömberg 2007). A key input for estimating flood risk is the spatial intensity of extreme rainfall events over a catchment. Current techniques for estimating extreme spatial rainfall rely on the use of an areal reduction factor (ARF) to convert intensity estimates of extreme point rainfall to extreme spatial rainfall. It is common practice to ignore the spatial variation in rainfall intensity and assume a fixed ARF applies over large regions. The aim of this paper is to introduce a new approach that explicitly incorporates the area and variation of spatial rainfall, referred to as intensity-frequencyduration area (IFDA). The IFDA approach uses spatially interpolated rainfall grids to directly provide an estimate of how spatial rainfall intensities vary with duration, frequency, and area for a location. An IFDA adds the extra dimension of area (A) to an IFD curve to account for spatial variation in intensity over a catchment
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