Antonia Sebastian

Examining the impact of land use/land cover characteristics on flood losses

Characteristics of the built environment and overall local-level land use patterns are increasingly being attributed to greater surface runoff, flooding and resulting economic losses from flood events. Specific configurations of impervious surfaces and land cover may be as important to determining a communitys flood risk as baseline environmental conditions. This study addresses this issue by statistically examining the impacts of adjacent land use and land cover (LULC) on flood damage recorded on parcels within a coastal watershed in southeast Texas. We analyse empirical models to identify the influence of different LULCs surrounding over 7900 properties claiming insured flood losses from 1999–2009. Results indicate that specific types of surrounding LULCs impact observed flood losses and provide guidance on how neighbourhoods can be developed more resiliently over the long term.

Delineating the Reality of Flood Risk and Loss in Southeast Texas

AbstractAlthough the 100-year floodplain is the traditional indicator of risk from flooding and a catalyst for mitigation decisions in the United States, increasing evidence indicates that this boundary is not sufficient in representing actual economic losses caused by floods. Although studies have demonstrated that up to 50% of losses occur outside floodplain boundaries, as of this writing it is believed little or no research has been conducted on the precise spatial characteristics of these losses or offers an alternative approach for depicting flood exposure at the local level. This perceived lack of inquiry is addressed by spatially examining the pattern of insured flood loss within the Clear Creek watershed near Houston as a first step in better understanding the relationship between floodplain boundaries and actual loss. First, property damage claims are mapped under the National Flood Insurance Program over an 11-year period from 1999 to 2009 and then these points of loss are analyzed in relation t...

Dynamic Modeling of Storm Surge and Inland Flooding in a Texas Coastal Floodplain

The purpose of this study is to analyze the combined effects of storm surge and inland rainfall on the floodplain of a coastal bayou in the Houston area by using dynamic hydraulic modeling. Most existing floodplains in the Houston area are defined using only rainfall as an input into steady-state hydraulic models and do not consider the impact of hurricane-induced storm surge on the floodplain. HEC-RAS, a one-dimensional flow model, was run for both steady- and unsteady-states to analyze the additional effect storm surge has on the coastal floodplain. Storm surge and rainfall data from Hurricane Ike were utilized to run an unsteady hydraulic model on Horsepen Bayou near Galveston Bay. The dynamic model generated a good match between the modeled hydrograph and measured data in the watershed. Additionally, a timing sensitivity analysis was completed by shifting the timing of the storm surge both earlier and later in time. The dynamic model revealed that the timing of both rainfall and storm surge play a sig...

Trends in flood losses in Europe over the past 150 years

Adverse consequences of floods change in time and are influenced by both natural and socio-economic trends and interactions. In Europe, previous studies of historical flood losses corrected for demographic and economic growth (‘normalized’) have been limited in temporal and spatial extent, leading to an incomplete representation of trends in losses over time. Here we utilize a gridded reconstruction of flood exposure in 37 European countries and a new database of damaging floods since 1870. Our results indicate that, after correcting for changes in flood exposure, there has been an increase in annually inundated area and number of persons affected since 1870, contrasted by a substantial decrease in flood fatalities. For more recent decades we also found a considerable decline in financial losses per year. We estimate, however, that there is large underreporting of smaller floods beyond most recent years, and show that underreporting has a substantial impact on observed trends.Flooding may cause loss of life and economic damage, therefore temporal changes need assessment. Here, the authors show that since 1870 there has been an increase in area inundated by floods in Europe, but a reduction in fatalities and economic losses, although caution that smaller floods remain underreported.

Flood Risk Delineation in the United States: How Much Loss Are We Capturing?

AbstractThe 100-year floodplain is the traditional indicator of flood risk and the area in which specific flood mitigation requirements are required to occur in the United States. However, recent s...

Case study results from southeast Houston, Texas: identifying the impacts of residential location on flood risk and loss

Despite the increasing economic losses from floods in coastal communities, little observational research has been done at a fine spatial scale to identify the relative influence of residential location in predicting adverse economic impacts. In response, this study conducts a parcel-level analysis of flood losses to identify the influence of specific location-based variables on property damage from multiple flood events. We statistically isolate the effect of multiple location-based characteristics on insured flood claims associated with two major coastal storms for over 7813 properties within the Clear Creek watershed southeast of Houston, Texas. Results indicate that location-based variables are among the strongest predictors for both, where seemingly subtle shifts in location add up to large dollar losses from flooding. These findings provide an increased understanding of the role of physical location within a flood-vulnerable region and how residential choice can be a major factor in exacerbating actual property loss.

A Copula-based bayesian network for modeling compound flood hazard from riverine and coastal interactions at the catchment scale: An application to the houston ship channel, Texas

Traditional flood hazard analyses often rely on univariate probability distributions; however, in many coastal catchments, flooding is the result of complex hydrodynamic interactions between multiple drivers. For example, synoptic meteorological conditions can produce considerable rainfall-runoff, while also generating wind-driven elevated sea-levels. When these drivers interact in space and time, they can exacerbate flood impacts, a phenomenon known as compound flooding. In this paper, we build a Bayesian Network based on Gaussian copulas to generate the equivalent of 500 years of daily stochastic boundary conditions for a coastal watershed in Southeast Texas. In doing so, we overcome many of the limitations of conventional univariate approaches and are able to probabilistically represent compound floods caused by riverine and coastal interactions. We model the resulting water levels using a one-dimensional (1D) steady-state hydraulic model and find that flood stages in the catchment are strongly affected by backwater effects from tributary inflows and downstream water levels. By comparing our results against a bathtub modeling approach, we show that simplifying the multivariate dependence between flood drivers can lead to an underestimation of flood impacts, highlighting that accounting for multivariate dependence is critical for the accurate representation of flood risk in coastal catchments prone to compound events.

Impacts of Hurricane Storm Surge on Infrastructure Vulnerability for an Evolving Coastal Landscape

AbstractPredicting coastal infrastructure reliability during hurricane events is important for risk-based design and disaster planning, including delineating viable emergency response routes. Previ...