The Impact of Rainfall Space‐Time Structure in Flood Frequency Analysis

Abstract

Flood hydrologic response is influenced by rainfall structure (i.e., variability in space and time). How this structure shapes flood frequency is unknown, and flood frequency analyses typically neglect or simplify potentially important aspects of rainfall variability. This study seeks to understand how rainfall structure impacts flood frequency. We use stochastic storm transposition combined with a 15‐year record of hourly, 4‐km2 radar rainfall to generate 10,000 synthetic extreme rain events. These events are resampled into four “scenarios” with differing spatial and temporal resolutions, which are used as input to a distributed hydrologic model. Analysis of variance is used to identify the proportions of total flood peak variability attributable to spatial and to temporal rainfall variability under two antecedent soil moisture conditions. We simulate peak discharges for recurrence intervals of 2 to 500 years for 1,343 subwatersheds ranging in size from 16 to 4,400 km2 in Turkey River in the Midwestern United States, which is situated in a typically humid continental climactic region. Antecedent soil moisture modulates the role of rainfall structure in simulated flood response, particularly for more frequent events and large watershed scales. Rainfall spatial structure is more important than temporal structure for drainage areas larger than approximately 2,000 km2 (approximately 200 km2) for wet (dry) initial soil conditions, especially when soils are dry, while the reverse is true for smaller subwatersheds. The results appear to be related to the differing propensities for surface and subsurface runoff production as a function of basin scale, event magnitude, and soil saturation. Our results suggest that hydrologic model‐based flood frequency analyses, and particularly efforts attempting to spanning a range of scales, must carefully consider rainfall structure.

Temperature effects on the spatial structure of heavy rainfall modify catchment hydro-morphological response

“…Spatio-temporal rainfall variability has been shown to play an important role in the hydro-morphological response of small-to medium-sized catchments (i.e. of the order of 10 1 -10 3 km 2 ), affecting streamflow and sediment transport volumes, peaks, and time to peaks (Arnaud et al, 2011;Bahat et al, 2009;Coulthard and Skinner, 2016;Kampf et al, 2016;Morin et al, 2006;Paschalis et al, 2014;Singh, 1997;Yakir and Morin, 2011;Zhu et al, 2018;Zoccatelli et al, 2011). Heavy rainfall events at these spatial scales have the potential to cover a given catchment entirely, thus increas-N. Peleg et al: Temperature effects on the spatial structure ing the sensitivity of the hydro-morphological response to the extreme event itself (Do et al, 2017;Sharma et al, 2018;Wasko and Sharma, 2017).…”

Temperature effects on heavy rainfall modify catchment hydro-morphological response

“…Spatio-temporal rainfall variability has been shown to play an important role in the hydro-morphological response of small to medium size catchments (i.e. in the order of 10 1 -10 3 km 2 ) affecting streamflow and sediment transport volumes, peaks and time to peaks (Arnaud et al, 2011;Bahat et al, 2009;Coulthard and Skinner, 2016;Kampf et al, 2016;Morin et al, 2006;Paschalis et al, 2014;Singh, 1997;Yakir and Morin, 2011;Zhu et al, 2018;Zoccatelli et al, 2011). Heavy rainfall events at these scales have the potential to cover a given catchment entirely, thus increasing the sensitivity of the hydro-morphological response to the extreme event itself (Do et al, 2017;Sharma et al, 2018;Wasko and Sharma, 2017).…”

“…Therefore, rainfall fields at high spatial and temporal resolution, at the scales appropriate to simulate rainfall convective features (i.e. 1 km and 10 min, or finer), are needed for hydrological and geomorphological climate change impact studies (Coulthard and Skinner, 2016;Gires et al, 2015;Li and Fang, 2016;Morin et al, 2006;Ochoa-Rodriguez et al, 2015;Peleg et al, 2015;Skinner et al, 2019;Zhu et al, 2018).…”

Application of storm transposition to the Middle Cedar Watershed

“…The research presented by Zhu et al ran 20 storm events for return periods ranging from 2 to 5 years, as determined by RainyDay for generic wet and dry soil moisture conditions (Zhu et al, 2018). This paper, in tandem with the work by Hayden et al, shows the possibilities for detailed analysis of watershed responses to varied flooding in hydrologic models using SST.…”

“…A study performed in Iowa's Turkey River Watershed examined the relationship of spatial and temporal distribution on the watershed for a variety of antecedent soil moisture conditions (Zhu, Wright, & Yu, 2018). This study used RainyDay to transpose storms with return periods ranging from 2-to 500-year events onto the Hillslope Link Model for the Turkey River…”