Determining 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

more »

... e 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 km 2 ), durations (1-4 days), and average recurrence intervals (ARI 2-100 years). The change in extreme spatial rainfall with respect to area varies markedly within each region suggesting that constant areal reduction factors for a region are inappropriate. Constant areal reduction factors are shown to underestimate extreme spatial rainfall intensities by 5-15%. The IFDA approach avoids these biases and is a promising new technique for use in design flood estimation. individual papers. This paper is part of the Journal of Hydrologic Engineering, © ASCE, ISSN 1084-0699. © ASCE 04015074-1 J. Hydrol. Eng. J. Hydrol. Eng., 2016, 21(3): 04015074 Downloaded from ascelibrary.org by The University of Adelaide on 04/27/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015074-2 J. Hydrol. Eng. J. Hydrol. Eng., 2016, 21(3): 04015074 Downloaded from ascelibrary.org by The University of Adelaide on 04/27/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015074-9 J. Hydrol. Eng. J. Hydrol. Eng., 2016, 21(3): 04015074 Downloaded from ascelibrary.org by The University of Adelaide on 04/27/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015074-10 J. Hydrol. Eng. J. Hydrol. Eng., 2016, 21(3): 04015074 Downloaded from ascelibrary.org by The University of Adelaide on 04/27/16. Copyright ASCE. For personal use only; all rights reserved. Assumes spatial interpolated estimates are appropriate © ASCE 04015074-11 J. Hydrol. Eng.