![]() In addition, policy totals in Texas began declining well before Biggert-Waters 2012, federal legislation that raised NFIP premiums for some policyholders. This decline occurred despite several large floods in Texas during that time, which tend to sharply increase flood-insurance penetration in other areas of the country. Numbers of policies peaked in 2008 and have declined every year since that time. Notably, and in contrast to the trend nationwide, the number of NFIP policies both in Harris County and in Texas has declined during the past several years (Figure 2). Texas represents about 12% of NFIP policies nationwide and about 10% of annual premiums to NFIP. Texas-wide, there are 593,115 policies in force, covering $161.2 billion, with $ 364.0 million in premiums. Over 40% of Texas NFIP policies are from Harris County. We also examined repetitive flood losses.Īs of June 30, 2017, Harris County policyholders held 249,212 NFIP flood insurance policies, covering $70.34 billion of assets, and generating $138.4 million in annual premiums. For the analysis here, we identified current policies and past claims in the City of Houston, Harris County, and Texas as a whole. We obtained databases of NFIP policies nationwide back to 1994 and insurance claims back to 1972. Since 1964, Harris County has had 27 federally declared disasters related to flooding and/or coastal storms. Texas has a long history of damaging flooding, and Houston has seen some of the worst of it, well before Harvey. History of Flood Damage and Exposure in Harris County More than that over 50% of estimated inundation occurred outside of any mapped flood zone. 29 completely filled Harris County’s 500-year floodplain. The 13.44% of inundation in the 500-year floodplain is very similar to the total portion of the study area in the mapped 500-year zone, suggesting that on average, flooding on Aug. About two-thirds of the inundation is outside of FEMA’s Special Flood Hazard Area, which is the so-called “100-year” floodplain, or area with a 1% or greater chance of flooding in any given year. ![]() In Table 1, the percentages of total flooded area illustrate the great intensity of flooding resulting from Harvey. Distribution of flood inundation in Harris County, Texas in different mapped flood zones. Reservoirs are overflowing, streams and rivers surging high over the surrounding floodplains, and highways and roads are now themselves rivers. The resulting inundation map shows the striking extent of flooding in Houston and provides context for the on-the-ground photos coming out of the area. Finally, we further compared the surface water extent with known pre-storm extents by flood-zone in order to determine flooding extent in each area in the portion of the county we assessed. We overlaid the resulting map on flood-zone boundaries from FEMA’s National Flood Hazard Layer and on other geographical data. In addition, this radar imagery is sensitive to standing water, making it an ideal tool for mapping the extent (but not depth) of flood water covering an area.Ī Sentinel-1 satellite passed over Houston on August 29, which we used to create a map that highlights water and flood inundation on the surface. The Sentinel-1 satellites carry radar sensors, which can scan the surface at night and through cloud cover. The Sentinel-1 system, which consists of two satellites, was launched by the European Space Agency. ![]() (2) Analyzed data from the US National Flood Insurance Program (NFIP) to look at the nature and pattern of flood exposure in Harris County, including Houston. 29, at the peak of flooding in many areas. (1) Processed radar data from the Sentinel-1A satellite from Aug. Our team in the Natural Hazards Research and Mitigation Group at the University of California, Davis conducted two sets of analyses to provide preliminary information on the pattern of flooding and to provide some context on historical flood damages in the Houston area. Even measurement of the flooding by visible-light based satellite has been impossible because the remnants of Hurricane Harvey have stalled over the Gulf Coast for the past week, dumping record precipitation and obscuring the skies from satellite view. The inundation is so widespread that detailed assessment has not yet been possible. At the present moment, little quantitative information is available about the extent of flooding or economic damages. The flooding now unfolding in the Houston area is a human and economic disaster likely to rank with Hurricanes Katrina and Sandy among the worst in US history. Located in Harris County, Texas, Houston is the 4 th most populous city in the US. By Nicholas Pinter, Nicholas Santos, and Rui Hui ![]()
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