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Nick Van De Giesen - One of the best experts on this subject based on the ideXlab platform.
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the influence of rainfall and catchment critical scales on urban Hydrological Response sensitivity
Water Resources Research, 2019Co-Authors: Elena Cristiano, Marie-claire Ten Veldhuis, Daniel B. Wright, James A Smith, Nick Van De GiesenAbstract:Interactions between spatial and temporal variability of rainfall and catchment characteristics strongly influence Hydrological Response. In urban areas, where runoff generation is fast due to high imperviousness degree, it is especially relevant to capture the high spatiotemporal rainfall variability. Significant progress has been made in the development of spatially distributed rainfall measurements and of distributed Hydrological models, to represent the variability of catchment's characteristics. Interactions between rainfall and basin scales on Hydrological Response sensitivity, however, needs deeper investigation. A previous study investigated the Hydrological Response in the small urbanized catchment of Cranbrook (8 km 2 , London, UK) and proposed three dimensionless “scale factors” to identify if the available rainfall resolution is sufficient to properly predict Hydrological Response. We aim to verify the applicability of these scale factors to larger scales, with a distinct physiographic setting, in Little Sugar Creek (111 km 2 , Charlotte, USA), to identify the required rainfall resolution and to predict model performance. Twenty-eight events were selected from a weather radar data set from the National Weather Radar Network, with a resolution of 1 km 2 and 15 min. Rainfall data were aggregated to coarser resolutions and used as input for a distributed Hydrological model. Results show that scale factors and associated thresholds are generally applicable for characterization of urban flood Response to rainfall across spatiotemporal scales. Additionally, application of scale factors in observation-based analysis supports identification of event characteristics that are poorly captured and critical improvements that need to be made before the model can benefit from high-resolution rainfall.
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critical scales to explain urban Hydrological Response an application in cranbrook london
Hydrology and Earth System Sciences, 2018Co-Authors: Elena Cristiano, Marie-claire Ten Veldhuis, Santiago Gaitan, Susana Ochoa Rodriguez, Nick Van De GiesenAbstract:Abstract. Rainfall variability in space and time, in relation to catchment characteristics and model complexity, plays an important role in explaining the sensitivity of Hydrological Response in urban areas. In this work we present a new approach to classify rainfall variability in space and time and we use this classification to investigate rainfall aggregation effects on urban Hydrological Response. Nine rainfall events, measured with a dual polarimetric X-Band radar instrument at the CAESAR site (Cabauw Experimental Site for Atmospheric Research, NL), were aggregated in time and space in order to obtain different resolution combinations. The aim of this work was to investigate the influence that rainfall and catchment scales have on Hydrological Response in urban areas. Three dimensionless scaling factors were introduced to investigate the interactions between rainfall and catchment scale and rainfall input resolution in relation to the performance of the model. Results showed that (1) rainfall classification based on cluster identification well represents the storm core, (2) aggregation effects are stronger for rainfall than flow, (3) model complexity does not have a strong influence compared to catchment and rainfall scales for this case study, and (4) scaling factors allow the adequate rainfall resolution to be selected to obtain a given level of accuracy in the calculation of Hydrological Response.
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Critical scales to explain urban Hydrological Response
Hydrology and Earth System Sciences Discussions, 2018Co-Authors: Elena Cristiano, Marie-claire Ten Veldhuis, Santiago Gaitan, Susana Ochoa Rodriguez, Nick Van De GiesenAbstract:Rainfall variability in space and time, in relation to catchment characteristics and model complexity, plays an important role in explaining the sensitivity of Hydrological Response in urban areas. In this work we present a new approach to classify rainfall variability in space and time and we use this classification to investigate rainfall aggregation effects on urban Hydrological Response. Nine rainfall events, measured with a Dual polarimetric X-Band radar at the CAESAR Site (Cabauw Experimental Site for Atmospheric Research, NL), were aggregated in time and space in order to obtain different resolution combinations. The aim of this work was to investigate the influence that rainfall and catchment scales have on Hydrological Response in urban areas. Three dimensionless scaling factors were introduced to investigate the interactions between rainfall and catchment scale and rainfall input resolution in relation to the performance of the model. Results showed that (1) rainfall classification based on cluster identification well represents the storm core, (2) aggregation effects are stronger for rainfall than flow, (3) model complexity does not have a strong influence compared to catchment and rainfall scales for this study case, (4) scaling factors allow to select the adequate rainfall resolution to obtain a given level of accuracy in the calculation of Hydrological Response.
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spatial and temporal variability of rainfall and their effects on Hydrological Response in urban areas a review
Hydrology and Earth System Sciences, 2016Co-Authors: Elena Cristiano, Marie-claire Ten Veldhuis, Nick Van De GiesenAbstract:In urban areas, Hydrological processes are characterized by high variability in space and time, making them sensitive to small-scale temporal and spatial rainfall variability. In the last decades new instruments, techniques, and methods have been developed to capture rainfall and Hydrological processes at high resolution. Weather radars have been introduced to estimate high spatial and temporal rainfall variability. At the same time, new models have been proposed to reproduce Hydrological Response, based on small-scale representation of urban catchment spatial variability. Despite these efforts, interactions between rainfall variability, catchment heterogeneity, and Hydrological Response remain poorly understood. This paper presents a review of our current understanding of Hydrological processes in urban environments as reported in the literature, focusing on their spatial and temporal variability aspects. We review recent findings on the effects of rainfall variability on Hydrological Response and identify gaps where knowledge needs to be further developed to improve our understanding of and capability to predict urban Hydrological Response.
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Spatial and temporal variability of rainfall and their effects on Hydrological Response in urban areas -– a review
2016Co-Authors: Elena Cristiano, Marie-claire Ten Veldhius, Nick Van De GiesenAbstract:Abstract. In urban areas, Hydrological processes are characterised by high variability in space and time, making them sensitive to small-scale temporal and spatial rainfall variability. In the last decades new instruments, techniques and methods have been developed to capture rainfall and Hydrological processes at high resolution. Weather radars have been introduced to estimate high spatial and temporal rainfall variability. At the same time, new models have been proposed to reproduce Hydrological Response, based on small-scale representation of urban catchment spatial variability. Despite these efforts, interaction between input variability and model resolution remains poorly understood, and further investigations are needed. This paper presents a review of our current understanding of Hydrological processes in urban environments as reported in the literature, focusing on their spatial and temporal variability. We review recent findings on the effects of rainfall variability on Hydrological Response and identify gaps where knowledge need to be further developed to improve our understanding of and capability to predict urban Hydrological Response.
P. J. Wallbrink - One of the best experts on this subject based on the ideXlab platform.
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effects of differing wildfire severities on soil wettability and implications for Hydrological Response
Journal of Hydrology, 2006Co-Authors: Stefan H. Doerr, W. H. Blake, Richard A Shakesby, C.j. Chafer, Geoffrey Humphreys, P. J. WallbrinkAbstract:Abstract Fire-induced or enhanced soil water repellency is often viewed as a key cause of the substantial increases in runoff and erosion following severe wildfires. In this study, the effects of different fire severities on soil water repellency are examined in eucalypt forest catchments in the Sandstone Tablelands near Sydney, burnt in 2001 and 2003. At sites affected by different fire severities and in long-unburnt control sites, repellency persistence was determined in situ and in the laboratory for surface and subsurface soil samples (n=846) using the Water Drop Penetration Time (WDPT) test. All long-unburnt samples were found to be water repellent, with severe to extreme persistence (>900 s) being dominant for surface (0–2.5 cm) and slight to moderate persistence (10–900 s) for subsurface (2.5–5 cm) soil, indicating naturally very high ‘background’ levels of repellency. In contrast to the generation or enhancement of repellency usually reported following forest fires of similar severity in previous studies, burning caused widespread destruction of repellency. The mineral soil depth to which repellency was destroyed (0.5–5 cm) was found to increase with burn severity. Below this charred wettable layer, persistence of pre-existing water repellency increased. Two years after the fire, the frequency of extreme repellency persistence was reduced in the surface and subsurface. However, recovery to pre-fire repellency levels had not been achieved. The associated Hydrological impacts of these fire effects are more complex than simply the enhancement of overland flow, runoff and soil erosion with increasing fire severity. For forest fires sufficiently severe to remove foliage and ground litter above already repellent soil, a more severe burn, in which there is destruction of surface soil repellency, would result in lower runoff Response compared to a burn insufficiently severe to destroy surface repellency. During storms intense enough to saturate the wettable surface rapidly, this layer may, however, be removed by overland flow, with potentially severe implications for soil fertility and seedbed survival, post-fire ecosystem recovery, and downstream sedimentation and water quality. The results demonstrate that existing fire severity classifications are not well suited to predicting fire impacts on soil Hydrological Responses and highlight the need for a new fire severity evaluation scheme. A scheme encompassing not only foliage and ground cover status, but also changes to surface and subsurface soil Hydrological properties, would provide a better prediction of the immediate Hydrological effects of wildfires on catchments such as flash flooding and erosion, and also of their time-to-recovery than current classifications allow. Such a scheme could prove invaluable given the future increase in fire frequency and severity predicted for many regions.
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Effects of differing wildfire severities on soil wettability and implications for Hydrological Response
Journal of Hydrology, 2006Co-Authors: Stefan H. Doerr, W. H. Blake, G. S. Humphreys, Richard A Shakesby, C.j. Chafer, P. J. WallbrinkAbstract:Fire-induced or enhanced soil water repellency is often viewed as a key cause of the substantial increases in runoff and erosion following severe wildfires. In this study, the effects of different fire severities on soil water repellency are examined in eucalypt forest catchments in the Sandstone Tablelands near Sydney, burnt in 2001 and 2003. At sites affected by different fire severities and in long-unburnt control sites, repellency persistence was determined in situ and in the laboratory for surface and subsurface soil samples (n=846) using the Water Drop Penetration Time (WDPT) test. All long-unburnt samples were found to be water repellent, with severe to extreme persistence (>900 s) being dominant for surface (0-2.5 cm) and slight to moderate persistence (10-900 s) for subsurface (2.5-5 cm) soil, indicating naturally very high 'background' levels of repellency. In contrast to the generation or enhancement of repellency usually reported following forest fires of similar severity in previous studies, burning caused widespread destruction of repellency. The mineral soil depth to which repellency was destroyed (0.5-5 cm) was found to increase with burn severity. Below this charred wettable layer, persistence of pre-existing water repellency increased. Two years after the fire, the frequency of extreme repellency persistence was reduced in the surface and subsurface. However, recovery to pre-fire repellency levels had not been achieved. The associated Hydrological impacts of these fire effects are more complex than simply the enhancement of overland flow, runoff and soil erosion with increasing fire severity. For forest fires sufficiently severe to remove foliage and ground litter above already repellent soil, a more severe burn, in which there is destruction of surface soil repellency, would result in lower runoff Response compared to a burn insufficiently severe to destroy surface repellency. During storms intense enough to saturate the wettable surface rapidly, this layer may, however, be removed by overland flow, with potentially severe implications for soil fertility and seedbed survival, post-fire ecosystem recovery, and downstream sedimentation and water quality. The results demonstrate that existing fire severity classifications are not well suited to predicting fire impacts on soil Hydrological Responses and highlight the need for a new fire severity evaluation scheme. A scheme encompassing not only foliage and ground cover status, but also changes to surface and subsurface soil Hydrological properties, would provide a better prediction of the immediate Hydrological effects of wildfires on catchments such as flash flooding and erosion, and also of their time-to-recovery than current classifications allow. Such a scheme could prove invaluable given the future increase in fire frequency and severity predicted for many regions. © 2005 Elsevier Ltd All rights reserved.
Elena Cristiano - One of the best experts on this subject based on the ideXlab platform.
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Evaluating critical rainfall and catchment scale influence on Hydrological Response in urban areas
2020Co-Authors: Elena Cristiano, M. C. Ten Veldhuis, Daniel B. Wright, James A Smith, N. Van De GiesenAbstract:Rainfall spatial and temporal variability are key points in the prediction of Hydrological Response. At the same time, catchment scale and characteristics also play important roles, especially in urban areas, where the high level of imperviousness combined with intense and localised rainfall causes fast Responses (Ochoa-Rodriguez et al., 2015). New instruments such as weather radars have been developed in recent decades able to better capture the spatial and temporal variability of storm events. At the same time, large improvements have been made to create high-resolution Hydrological models that are able to represent the catchment with a high level of detail. However, the interactions between rainfall and catchment variability and their effects on the Hydrological Response remains poorly understood. In this work, we aim to evaluate the critical space and time scales that characterize rainfall variability and catchment characteristics in relation to Hydrological Response in urban areas. Critical scales based on dimensionless parameters developed in a previous work (Cristiano et al, 2018) will be evaluated for two urban areas in different climatological regions, one in Europe and one in the US.
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the influence of rainfall and catchment critical scales on urban Hydrological Response sensitivity
Water Resources Research, 2019Co-Authors: Elena Cristiano, Marie-claire Ten Veldhuis, Daniel B. Wright, James A Smith, Nick Van De GiesenAbstract:Interactions between spatial and temporal variability of rainfall and catchment characteristics strongly influence Hydrological Response. In urban areas, where runoff generation is fast due to high imperviousness degree, it is especially relevant to capture the high spatiotemporal rainfall variability. Significant progress has been made in the development of spatially distributed rainfall measurements and of distributed Hydrological models, to represent the variability of catchment's characteristics. Interactions between rainfall and basin scales on Hydrological Response sensitivity, however, needs deeper investigation. A previous study investigated the Hydrological Response in the small urbanized catchment of Cranbrook (8 km 2 , London, UK) and proposed three dimensionless “scale factors” to identify if the available rainfall resolution is sufficient to properly predict Hydrological Response. We aim to verify the applicability of these scale factors to larger scales, with a distinct physiographic setting, in Little Sugar Creek (111 km 2 , Charlotte, USA), to identify the required rainfall resolution and to predict model performance. Twenty-eight events were selected from a weather radar data set from the National Weather Radar Network, with a resolution of 1 km 2 and 15 min. Rainfall data were aggregated to coarser resolutions and used as input for a distributed Hydrological model. Results show that scale factors and associated thresholds are generally applicable for characterization of urban flood Response to rainfall across spatiotemporal scales. Additionally, application of scale factors in observation-based analysis supports identification of event characteristics that are poorly captured and critical improvements that need to be made before the model can benefit from high-resolution rainfall.
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Effects of rainfall and catchment scales on Hydrological Response sensitivity in urban areas
2019Co-Authors: Elena CristianoAbstract:Spatial and temporal rainfall variability play an important role in generation of pluvial flooding. In urban areas, this phenomenon has increased in the last decades, due in particular to an intensification of urbanization and imperviousness degree. In fact, population is growing and moving from rural areas to cities, which are becoming more and more urbanized and densely populated. The increase of urbanization and related increase of imperviousness degree, combined with short and intense rainfall events, caused by climate changes, result in a fast Hydrological Response, with high probability of flooding. Hydrological models can represent the overall flow behaviour but they remain poorly capable of predicting flow peaks, especially in urban areas. In view of this, a better knowledge of the Hydrological Response of the urban catchment is needed to improve flood prediction and prevent damages caused by pluvial flooding. Due to the high variability of catchment characteristics at small scale, urban runoff processes are particularly sensitive to spatial and temporal variability of rainfall. For this reason, high resolution data are required for accurate runoff estimation. Rainfall is generally measured with rain gauges, which provide accurate measurements in a specific point, but they are not able to fully describe rainfall variability in space. New technologies, such as weather radars, have been used in recent decades to estimate rainfall intensity. Although these instruments provide an indirect measurement of rainfall and require good calibration and error corrections, they can provide rainfall distribution in space and time, which is fundamental to investigate the Hydrological Response. Rainfall characteristics, such as intensity, total depth, storm velocity and intermittency, strongly affect the Hydrological Response of the system and it is important to properly characterize them to estimate the runoff. Catchment characteristics, such as drainage area, drainage network, imperviousness degree and slope, and their representation in Hydrological models also play an important role in the prediction of Hydrological Response. At present, combined effects of rainfall and catchment characteristics and scales on urban Hydrological Response needs further investigations…
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critical scales to explain urban Hydrological Response an application in cranbrook london
Hydrology and Earth System Sciences, 2018Co-Authors: Elena Cristiano, Marie-claire Ten Veldhuis, Santiago Gaitan, Susana Ochoa Rodriguez, Nick Van De GiesenAbstract:Abstract. Rainfall variability in space and time, in relation to catchment characteristics and model complexity, plays an important role in explaining the sensitivity of Hydrological Response in urban areas. In this work we present a new approach to classify rainfall variability in space and time and we use this classification to investigate rainfall aggregation effects on urban Hydrological Response. Nine rainfall events, measured with a dual polarimetric X-Band radar instrument at the CAESAR site (Cabauw Experimental Site for Atmospheric Research, NL), were aggregated in time and space in order to obtain different resolution combinations. The aim of this work was to investigate the influence that rainfall and catchment scales have on Hydrological Response in urban areas. Three dimensionless scaling factors were introduced to investigate the interactions between rainfall and catchment scale and rainfall input resolution in relation to the performance of the model. Results showed that (1) rainfall classification based on cluster identification well represents the storm core, (2) aggregation effects are stronger for rainfall than flow, (3) model complexity does not have a strong influence compared to catchment and rainfall scales for this case study, and (4) scaling factors allow the adequate rainfall resolution to be selected to obtain a given level of accuracy in the calculation of Hydrological Response.
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Critical scales to explain urban Hydrological Response
Hydrology and Earth System Sciences Discussions, 2018Co-Authors: Elena Cristiano, Marie-claire Ten Veldhuis, Santiago Gaitan, Susana Ochoa Rodriguez, Nick Van De GiesenAbstract:Rainfall variability in space and time, in relation to catchment characteristics and model complexity, plays an important role in explaining the sensitivity of Hydrological Response in urban areas. In this work we present a new approach to classify rainfall variability in space and time and we use this classification to investigate rainfall aggregation effects on urban Hydrological Response. Nine rainfall events, measured with a Dual polarimetric X-Band radar at the CAESAR Site (Cabauw Experimental Site for Atmospheric Research, NL), were aggregated in time and space in order to obtain different resolution combinations. The aim of this work was to investigate the influence that rainfall and catchment scales have on Hydrological Response in urban areas. Three dimensionless scaling factors were introduced to investigate the interactions between rainfall and catchment scale and rainfall input resolution in relation to the performance of the model. Results showed that (1) rainfall classification based on cluster identification well represents the storm core, (2) aggregation effects are stronger for rainfall than flow, (3) model complexity does not have a strong influence compared to catchment and rainfall scales for this study case, (4) scaling factors allow to select the adequate rainfall resolution to obtain a given level of accuracy in the calculation of Hydrological Response.
G. Nord - One of the best experts on this subject based on the ideXlab platform.
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how does initial soil moisture influence the Hydrological Response a case study from southern france
Hydrology and Earth System Sciences, 2018Co-Authors: M. Uber, J.p. Vandervaere, I. Braud, C. Legout, G. Molinié, Maik Heistermann, G. NordAbstract:Abstract. The Cevennes–Vivarais region in southern France is prone to heavy rainfall that can lead to flash floods which are one of the most hazardous natural risks in Europe. The results of numerous studies show that besides rainfall and physical catchment characteristics the catchment's initial soil moisture also impacts the Hydrological Response to rain events. The aim of this paper is to analyze the relationship between catchment mean initial soil moisture θ ini and the Hydrological Response that is quantified using the event-based runoff coefficient ϕev in the two nested catchments of the Gazel (3.4 km 2 ) and the Claduegne (43 km 2 ). Thus, the objectives are twofold: (1) obtaining meaningful estimates of soil moisture at catchment scale from a dense network of in situ measurements and (2) using this estimate of θ ini to analyze its relation with ϕev calculated for many runoff events. A sampling setup including 45 permanently installed frequency domain reflectancy probes that continuously measure soil moisture at three depths is applied. Additionally, on-alert surface measurements at ≈10 locations in each one of 11 plots are conducted. Thus, catchment mean soil moisture can be confidently assessed with a standard error of the mean of ≤1.7 vol % over a wide range of soil moisture conditions. The ϕev is calculated from high-resolution discharge and precipitation data for several rain events with a cumulative precipitation Pcum ranging from less than 5 mm to more than 80 mm. Because of the high uncertainty of ϕev associated with the hydrograph separation method, ϕev is calculated with several methods, including graphical methods, digital filters and a tracer-based method. The results indicate that the Hydrological Response depends on θ ini : during dry conditions ϕev is consistently below 0.1, even for events with high and intense precipitation. Above a threshold of θ ini = 34 vol % ϕev can reach values up to 0.99 but there is a high scatter. Some variability can be explained with a weak correlation of ϕev with Pcum and rain intensity, but a considerable part of the variability remains unexplained. It is concluded that threshold-based methods can be helpful to prevent overestimation of the Hydrological Response during dry catchment conditions. The impact of soil moisture on the Hydrological Response during wet catchment conditions, however, is still insufficiently understood and cannot be generalized based on the present results.
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How does initial soil moisture influence the Hydrological Response? A case study from southern France
Hydrology and Earth System Sciences, 2018Co-Authors: M. Uber, J.p. Vandervaere, I. Braud, M. Heisterman, C. Legout, G. Molinié, G. NordAbstract:The Cévennes-Vivarais region in southern France is prone to heavy rainfall that can lead to flash floods which are one of the most hazardous natural risks in Europe. The results of numerous studies show that besides rainfall and physical catchment characteristics the catchment's initial soil moisture also impacts the Hydrological Response to rain events. The aim of this paper is to analyze the relationship between catchment mean initial soil moisture e-ini and the Hydrological Response that is quantified using the eventbased runoff coefficient ev in the two nested catchments of the Gazel (3.4 km2) and the Claduègne (43 km2). Thus, the objectives are twofold: (1) obtaining meaningful estimates of soil moisture at catchment scale from a dense network of in situ measurements and (2) using this estimate of e-inito analyze its relation with ev calculated for many runoff events. A sampling setup including 45 permanently installed frequency domain reflectancy probes that continuously measure soil moisture at three depths is applied. Additionally, onalert surface measurements at 10 locations in each one of 11 plots are conducted. Thus, catchment mean soil moisture can be confidently assessed with a standard error of the mean of 1:7 vol% over a wide range of soil moisture conditions. The ev is calculated from high-resolution discharge and precipitation data for several rain events with a cumulative precipitation Pcum ranging from less than 5mm to more than 80 mm. Because of the high uncertainty of ev associated with the hydrograph separation method, ev is calculated with several methods, including graphical methods, digital filters and a tracer-based method. The results indicate that the Hydrological Response depends one ini: during dry conditions ev is consistently below 0.1, even for events with high and intense precipitation. Above a threshold of e ini D 34 vol% ev can reach values up to 0.99 but there is a high scatter. Some variability can be explained with a weak correlation of ev with Pcum and rain intensity, but a considerable part of the variability remains unexplained. It is concluded that threshold-based methods can be helpful to prevent overestimation of the Hydrological Response during dry catchment conditions. The impact of soil moisture on the Hydrological Response during wet catchment conditions, however, is still insufficiently understood and cannot be generalized based on the present results.
M. Uber - One of the best experts on this subject based on the ideXlab platform.
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how does initial soil moisture influence the Hydrological Response a case study from southern france
Hydrology and Earth System Sciences, 2018Co-Authors: M. Uber, J.p. Vandervaere, I. Braud, C. Legout, G. Molinié, Maik Heistermann, G. NordAbstract:Abstract. The Cevennes–Vivarais region in southern France is prone to heavy rainfall that can lead to flash floods which are one of the most hazardous natural risks in Europe. The results of numerous studies show that besides rainfall and physical catchment characteristics the catchment's initial soil moisture also impacts the Hydrological Response to rain events. The aim of this paper is to analyze the relationship between catchment mean initial soil moisture θ ini and the Hydrological Response that is quantified using the event-based runoff coefficient ϕev in the two nested catchments of the Gazel (3.4 km 2 ) and the Claduegne (43 km 2 ). Thus, the objectives are twofold: (1) obtaining meaningful estimates of soil moisture at catchment scale from a dense network of in situ measurements and (2) using this estimate of θ ini to analyze its relation with ϕev calculated for many runoff events. A sampling setup including 45 permanently installed frequency domain reflectancy probes that continuously measure soil moisture at three depths is applied. Additionally, on-alert surface measurements at ≈10 locations in each one of 11 plots are conducted. Thus, catchment mean soil moisture can be confidently assessed with a standard error of the mean of ≤1.7 vol % over a wide range of soil moisture conditions. The ϕev is calculated from high-resolution discharge and precipitation data for several rain events with a cumulative precipitation Pcum ranging from less than 5 mm to more than 80 mm. Because of the high uncertainty of ϕev associated with the hydrograph separation method, ϕev is calculated with several methods, including graphical methods, digital filters and a tracer-based method. The results indicate that the Hydrological Response depends on θ ini : during dry conditions ϕev is consistently below 0.1, even for events with high and intense precipitation. Above a threshold of θ ini = 34 vol % ϕev can reach values up to 0.99 but there is a high scatter. Some variability can be explained with a weak correlation of ϕev with Pcum and rain intensity, but a considerable part of the variability remains unexplained. It is concluded that threshold-based methods can be helpful to prevent overestimation of the Hydrological Response during dry catchment conditions. The impact of soil moisture on the Hydrological Response during wet catchment conditions, however, is still insufficiently understood and cannot be generalized based on the present results.
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How does initial soil moisture influence the Hydrological Response? A case study from southern France
Hydrology and Earth System Sciences, 2018Co-Authors: M. Uber, J.p. Vandervaere, I. Braud, M. Heisterman, C. Legout, G. Molinié, G. NordAbstract:The Cévennes-Vivarais region in southern France is prone to heavy rainfall that can lead to flash floods which are one of the most hazardous natural risks in Europe. The results of numerous studies show that besides rainfall and physical catchment characteristics the catchment's initial soil moisture also impacts the Hydrological Response to rain events. The aim of this paper is to analyze the relationship between catchment mean initial soil moisture e-ini and the Hydrological Response that is quantified using the eventbased runoff coefficient ev in the two nested catchments of the Gazel (3.4 km2) and the Claduègne (43 km2). Thus, the objectives are twofold: (1) obtaining meaningful estimates of soil moisture at catchment scale from a dense network of in situ measurements and (2) using this estimate of e-inito analyze its relation with ev calculated for many runoff events. A sampling setup including 45 permanently installed frequency domain reflectancy probes that continuously measure soil moisture at three depths is applied. Additionally, onalert surface measurements at 10 locations in each one of 11 plots are conducted. Thus, catchment mean soil moisture can be confidently assessed with a standard error of the mean of 1:7 vol% over a wide range of soil moisture conditions. The ev is calculated from high-resolution discharge and precipitation data for several rain events with a cumulative precipitation Pcum ranging from less than 5mm to more than 80 mm. Because of the high uncertainty of ev associated with the hydrograph separation method, ev is calculated with several methods, including graphical methods, digital filters and a tracer-based method. The results indicate that the Hydrological Response depends one ini: during dry conditions ev is consistently below 0.1, even for events with high and intense precipitation. Above a threshold of e ini D 34 vol% ev can reach values up to 0.99 but there is a high scatter. Some variability can be explained with a weak correlation of ev with Pcum and rain intensity, but a considerable part of the variability remains unexplained. It is concluded that threshold-based methods can be helpful to prevent overestimation of the Hydrological Response during dry catchment conditions. The impact of soil moisture on the Hydrological Response during wet catchment conditions, however, is still insufficiently understood and cannot be generalized based on the present results.
