Abstract. The impact of spatial and temporal variability of rainfall on hydrological response remains poorly understood, in particular in urban catchments due to their strong variability in land use, a high degree of imperviousness and the presence of stormwater infrastructure. In this study, we analyze the effect of storm scale, position and movement in relation to basin scale and flow-path network structure on urban hydrological response. A catalog of 279 peak events was extracted from a high-quality observational dataset covering 15 years of flow observations and radar rainfall data for five (semi)urbanized basins ranging from 7.0 to 111.1 km2 in size. Results showed that the largest peak flows in the event catalog were associated with storm core scales exceeding basin scale, for all except the largest basin. Spatial scale of flood-producing storm events in the smaller basins fell into two groups: storms of large spatial scales exceeding basin size or small, concentrated events, with storm core much smaller than basin size. For the majority of events, spatial rainfall variability was strongly smoothed by the flow-path network, increasingly so for larger basin size. Correlation analysis showed that position of the storm in relation to the flow-path network was significantly correlated with peak flow in the smallest and in the two more urbanized basins. Analysis of storm movement relative to the flow-path network showed that direction of storm movement, upstream or downstream relative to the flow-path network, had little influence on hydrological response. Slow-moving storms tend to be associated with higher peak flows and longer lag times. Unexpectedly, position of the storm relative to impervious cover within the basins had little effect on flow peaks. These findings show the importance of observation-based analysis in validating and improving our understanding of interactions between the spatial distribution of rainfall and catchment variability.
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Contrasting rainfall-runoff characteristics of floods in desert and Mediterranean basins
Abstract. Catchment-scale hydrological studies on drylands are lacking because of thescarcity of consistent data: observations are often available at the plotscale, but their relevance for the catchment scale remains unclear. Adatabase of 24 years of stream gauge discharge and homogeneoushigh-resolution radar data over the eastern Mediterranean allows us to describe the properties of floods over catchments spanning from desert toMediterranean climates, and we note that the data set is mostly of moderateintensity floods. Comparing two climatic regions, desert and Mediterranean,we can better identify specific rainfall-runoff properties. Despite the large differences in rainfall forcing between the two regions, the resulting unitpeak discharges and runoff coefficients are comparable. Rain depth andantecedent conditions are the most important properties to shape floodresponse in Mediterranean areas. In deserts, instead, storm core propertiesdisplay a strong correlation with unit peak discharge and, to a lesser extent,with runoff coefficient. In this region, an inverse correlation with meancatchment annual precipitation suggests also a strong influence of localsurface properties. Preliminary analyses suggest that floods in catchmentswith wet headwater and dry lower section are more similar to desertcatchments, with a strong influence of storm core properties on runoffgeneration.
more » « less- Award ID(s):
- 1632048
- PAR ID:
- 10113327
- Date Published:
- Journal Name:
- Hydrology and Earth System Sciences
- Volume:
- 23
- Issue:
- 6
- ISSN:
- 1607-7938
- Page Range / eLocation ID:
- 2665 to 2678
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The relationship between catchment storage and discharge is nonlinear. The dynamicity of this relationship is dependent on the distance of the storage measurement from the stream, the depth of the soil moisture (SM) measurement, antecedent SM storage, and precipitation characteristics. Understanding the relative influence of these factors is critical for interpreting runoff generation processes and predicting discharge. In this study, we used a hysteresis index approach and analysed the nonlinear dynamics of catchment storage–discharge relationship across points, hillslope and catchment scales, and their controlling factors. A small headwater forested catchment located in the southern part of the Sierra Nevada region, California, was selected as a case study. In this Mediterranean catchment, the anticlockwise class IV hysteresis loop, indicating an earlier discharge peak than SM, was observed as a prevalent hysteresis class across all the scales, irrespective of seasons (i.e., dry vs. wet) and years (i.e., normal vs. drought). A few clockwise hysteresis loops were observed at the shallow depths (10 and 30 cm) of upslope and lower slope topographic positions. Further, we found a shorter lag time between SM peak to discharge peak at 60 and 90 cm soil depths during the wet season, and during the drought period. The shorter lag at the deeper depth was due to the presence of subsurface flow during high antecedent SM storage conditions and preferential flow through the soil pores during the drought periods. The variability in hysteresis at catchment and hillslope scales was controlled by peak rainfall intensity and antecedent SM storage. However, rainfall characteristics (intensity and depth) were major governing factors for most of the point scale locations. Overall, the current study highlighted the role of SM sensor's location in characterizing storage–discharge behaviour.
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/hess-23-2665-2019
