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51.
Determining the extent of flooding is an important role of the hydrological research community and provides a vital service to planners and engineers. For large river systems located within distant settings it is practical to utilize a remote sensing approach. This study combines a remote sensing and geomorphic approach to delineate the extent of a large hurricane generated flood event in the lower Pánuco basin (98,227 km2), the seventh largest river system draining into the Gulf of Mexico. The lower Pánuco basin is located within the coastal plain of eastern Mexico and has a complex alluvial valley. Data sources included a Landsat 5TM and Landsat 7ETM+ scene, and topographic and particle size data from fieldwork and laboratory analysis. The Landsat 5TM image was acquired after the peak of a large flood event in 1993, whereas the Landsat 7ETM+ scene was acquired during the dry season in 2000. The increasing number of days between flood crest and the date of flood image acquisition along the river valley provided the opportunity to examine several methods of flood delineation and to consider differences in floodplain geomorphology. Backswamp environments were easily delineated in flooded reaches within the Panuco and Tamuin valleys, whereas in the Moctezuma valley more sophisticated methods were required because of the greater time between image acquisition and flood peak, and the complex floodplain topography. This included Principal Component (PC) analysis and image classification. Within the floodplain, residual Holocene terraces complicated flood mapping. Classification of both images allowed consideration of the influence of permanent standing water. Although the flooded areas were greater in the lower reaches of the study area, because this portion of the valley contained large floodplain lakes, the amount of inundation was actually lower. Remote sensing offers the ability to examine large alluvial valleys in distant settings but does not imply that geomorphic criteria should be excluded. Indeed, because of heterogeneous floodplain topography this study illustrates the importance of including field based geomorphic analysis so that the complexity of distinct floodplain environments are considered. The findings from this study are significant because most remote sensing data obtained for the purpose of flood mapping will not coincide with the flood crest. Thus, this study provides an appropriate method for mapping flood inundation in large and complex floodplain settings after flood crest recession. 相似文献
52.
A Note on the Drag of the Sea Surface at Hurricane Winds 总被引：7，自引：0，他引：7
V. K. Makin 《Boundary-Layer Meteorology》2005,115(1):169-176
Based on the solution of the turbulent kinetic energy balance equation for the airflow in the regime of limited saturation by suspended sea-spray droplets, some experimental evidence, and simple arguments, a resistance law of the sea surface at hurricane winds is derived. It predicts the reduction of the drag coefficient for the wind speed exceeding hurricane values of 30–40 m s -1 in agreement with field data. 相似文献
53.
A feasible methodology for landslide susceptibility assessment in developing countries: A case-study of NW Nicaragua after Hurricane Mitch 总被引：1，自引：0，他引：1
Marta Guinau Raimon Palls Joan Manuel Vilaplana RISKNAT Research Group 《Engineering Geology》2005,80(3-4):316-327
In October 1998, Hurricane Mitch triggered a large number of landslides (mainly debris flows) in Honduras and Nicaragua, resulting in a high death toll and in considerable damage to property. In recent years, a number of risk assessment methodologies have been devised to mitigate natural disasters. However, due to scarcity of funds and lack of specialised personnel few of these methodologies are accessible to developing countries. To explore the potential application of relatively simple and affordable landslide susceptibility methodologies in such countries, we focused on a region in NW Nicaragua which was among the most severely hit during the Mitch event. Our study included (1) detailed field work to produce a high-resolution inventory landslide map at 1 : 10,000 scale, and (2) a selection of the relevant instability factors from a Terrain Units Map which had previously been generated in a project for rural development. Based on the combination of these two datasets and using GIS tools we developed a comparative analysis of failure-zones and terrain factors in an attempt to classify the land into zones according to the propensity to landslides triggered by heavy rainfalls. The resulting susceptibility map was validated by using a training and a test zone, providing results comparable to those reached in studies based in more sophisticated methodologies. Thus, we provide an example of a methodology which is simple enough to be fully comprehended by non-specialised technicians and which could be of help in landslide risk mitigation through implementation of non-structural measures, such as land planning or emergency measures. 相似文献
54.
This article describes the challenges confronting local authorities who must decide if and when to initiate evacuations from
tropical cyclones. This problem can be decomposed into the behavior of the hurricane that is relevant to evacuation and the
behavior of evacuees that is relevant to the hurricane. The uncertain behavior of these two systems can be modeled in an evacuation
management decision support system (EMDSS). The hurricane EMDSS described here displays information about the minimum, most,
and maximum probable evacuation time estimates (ETEs) in comparison to the earliest, most, and latest probable estimated times
of arrival (ETAs) for storm conditions. In addition, EMDSS calculates the cost of false positive (the economic cost of an
evacuation) and false negative (lives lost in a late evacuation) decision errors. EMDSS is being used in experiments to assess
different information displays, team compositions, community characteristics, and hurricane scenarios. In addition, it will
be used in training and actual hurricane operations. Finally, definition of the program’s requirements has identified further
research needed to build a better empirical base for its input data. 相似文献
55.
This study examines the effect of severe wind events on the mean and variance of housing price indices of six metropolitan
statistical areas (MSA) that are vulnerable to hurricanes and/or tornadoes. The research focuses on three areas that experienced
significant tornado activity (Fort Worth-Arlington, Nashville, and Oklahoma City) and three hurricane-prone areas (Corpus
Christi, Miami, and Wilmington, NC). An econometric time series model that captures the housing market responses to severe
windstorms is utilized. The model estimates changes in the local housing price index (HPI) as a function of several control
variables as well as dichotomous variables that correspond to the tornadoes and hurricanes. As expected, the statistical findings
indicate an immediate but short-lived decline in housing prices following a tornado or hurricane. Somewhat surprising is the
result that the impact on the housing market is remarkably consistent whether the wind event was a hurricane or a tornado.
Hurricanes and tornadoes are vastly different in terms of the point probabilities of a hit, the scope of the affected area
and the lead time that supports last minute preparation to mitigate damage. It appears that the market response to destruction
of real property does not distinguish between the types of wind event that produced the damage to the region. Results suggest
that windstorms result in an immediate one-half to two percent reduction in total MSA housing value. This corresponds to a
range of $34 million to $580 million in lost housing value. Estimates indicate some differences in how long market values
continue to decline in the periods following the wind event; however, most of the decline occurs within four quarters after
the windstorm. These differences can be attributed to the particular time series characteristics of the specific housing markets
and their respective housing price indices. The market serves the purpose of integrating and normalizing the losses. In so
doing the market provides a metric— a method for calibrating and comparing structural damage caused by different phenomenon.
相似文献
| Yongsheng WangEmail: |
56.
The oceanic mixed layer (OML) response to an idealized hurricane with different propagation speeds is investigated using a
two-layer reduced gravity ocean model. First, the model performances are examined with respect to available observations relative
to Hurricane Frances (2004). Then, 11 idealized simulations are performed with a Holland (Mon Weather Rev 108(8):1212–1218,
1980) symmetric wind profile as surface forcing with storm propagation speeds ranging from 2 to 12 m s−1. By varying this parameter, the phasing between atmospheric and oceanic scales is modified. Consequently, it leads to different
momentum exchanges between the hurricane and the OML and to various oceanic responses. The present study determines how OML
momentum and heat budgets depend on this parameter. The kinetic energy flux due to surface wind stress is found to strongly
depend on the propagation speed and on the cross-track distance from the hurricane center. A resonant regime between surface
winds and near-inertial currents is clearly identified. This regime maximizes locally the energy flux into the OML. For fast-moving
hurricanes (>6 m s−1), the ratio of kinetic energy converted into turbulence depends only on the wind stress energy input. For slow-moving hurricanes
(<6 m s−1), the upwelling induced by current divergence enhances this conversion by shallowing the OML depth. Regarding the thermodynamic
response, two regimes are identified with respect to the propagation speed. For slow-moving hurricanes, the upwelling combined
with a sharp temperature gradient at the OML base formed in the leading part of the storm maximizes the oceanic heat loss.
For fast propagation speeds, the resonance mechanism sets up the cold wake on the right side of the hurricane track. These
results suggest that the propagation speed is a parameter as important as the surface wind speed to accurately describe the
oceanic response to a moving hurricane. 相似文献
57.
Development of storm surge which led to flooding in St. Bernard Polder during Hurricane Katrina 总被引：2，自引：0，他引：2
Hurricane Katrina caused devastating flooding in St. Bernard Parish, Louisiana. Storm surge surrounded the polder that comprises heavily populated sections of the Parish in addition to the Lower 9th Ward section of Orleans Parish. Surge propagated along several pathways to reach levees and walls around the polder's periphery. Extreme water levels led to breaches in the levee/wall system which, along with wave overtopping and steady overflow, led to considerable flood water entering the polder. Generation and evolution of the storm surge as it propagated into the region is examined using results from the SL15 regional application of the ADCIRC storm surge model. Fluxes of water into the region through navigation channels are compared to fluxes which entered through Lake Borgne and over inundated wetlands surrounding the lake. Fluxes through Lake Borgne and adjacent wetlands were found to be the predominant source of water reaching the region. Various sources of flood water along the polder periphery are examined. Flood water primarily entered through the east and west sides of the polder. Different peak surges and hydrograph shapes were experienced along the polder boundaries, and reasons for the spatial variability in surge conditions are discussed. 相似文献
58.
Wetlands are the second-most valuable natural resource on Earth but have declined by approximately 70 % since 1900. Restoration and conservation efforts have succeeded in some areas through establishment of refuges where anthropogenic impacts are minimized. However, these areas are still prone to wetland damage caused by natural disasters. Severe storms such as Hurricane Irma, which made landfall as a Category 3 hurricane in southwest Florida (USA) on September 11, 2017, can cause the destruction of mangroves and other wetland habitat. Multispectral images from commercial satellites provide a means to assess the extent of the damage to different wetland habitat types with high spatial resolution (2 m pixels or finer) over large areas. Using such images presents a number of challenges, including deriving consistent and accurate classification of wetland and non-wetland vegetation. Machine learning methods have demonstrated high-accuracy mapping capabilities on small spatial scales, but require a large amount of robust training data. Meanwhile, ambitious efforts to map larger areas at finer resolutions may use hundreds of thousands of images, and therefore encounter Big-Data processing challenges. Large-scale efforts face the dilemma of adopting traditional mapping methods that may lend themselves to Big Data analytics but may result in accuracies that are inferior to new methods, or move to machine learning methods, which require robust training data. Given these considerations, we describe a version of the traditional Decision Tree (DT) approach and compare two common machine learning methods to derive land cover classes using a WorldView-2 image collected on November 12, 2018 to include one growing season after Hurricane Irma affected this area. Specifically, we compared the Support Vector Machine [SVM] and Neural Network [NN] methods, trained and validated with separate ground-truth datasets collected during a robust field campaign. Overall accuracies were only marginally different (85 % NN vs 83 % each DT and SVM), but healthy mangroves were more accurately identified with the DT (91 % vs 88 % NN and 86 % SVM), and degraded mangroves were more accurately identified with NN (62 % vs 57 % NN and 38 % DT). These results, combined with their respective training requirements, have implications for the direction with which large-scale high-resolution mapping of coastal habitats proceeds. 相似文献
59.
Potential impacts of 0.5 and 1.0 m of relative sea level rise (RSLR) on hurricane surge and waves in southeast Louisiana are investigated using the numerical storm surge model ADCIRC and the nearshore spectral wave model STWAVE. The models were applied for six hypothetic hurricanes that produce approximately 100 yr water levels in southeastern Louisiana. In areas of maximum surge, the impact of RSLR on surge was generally linear (equal to the RSLR). In wetland or wetland-fronted areas of moderate peak surges (2-3 m), the surge levels were increased by as much as 1-3 m (in addition to the RSLR). The surge increase is as much as double and triple the RSLR over broad areas and as much as five times the RSLR in isolated areas. Waves increase significantly in shallow areas due to the combined increases in water depth due to RSLR and surge increases. Maximum increases in wave height for the modeled storms were 1-1.5 m. Surge propagation over broad, shallow, wetland areas is highly sensitive to RSLR. Wave heights also generally increased for all RSLR cases. These increases were significant (0.5-1.5 m for 1 m RSLR), but less dramatic than the surge increases. 相似文献
60.
A hydrodynamics-based surge scale for hurricanes 总被引：2，自引：0，他引：2
Record hurricane surges over the last several years have demonstrated the need for an improved surge hazard warning scale for hurricanes. Here, a simple hydrodynamics-based surge scale for hurricane surge hazard is presented. This surge scale incorporates readily available meteorological information along with regional-scale bathymetry into a single measure of expected surge levels at the coast. We further outline an approach for estimating expected flood inundation and damages based on the alongshore extent of high surges during hurricanes. Comparisons between this new surge scale and historical hurricane observations show a measurable improvement over existing surge indices, including the Saffir-Simpson scale. It is anticipated that the proposed surge scale will improve public awareness of surge hazard and assist governments in communicating critical decisions regarding evacuation and emergency response. 相似文献