Harvey Now Driving Catastrophic Flooding Across Houston Metropolitan Region

(For media statement, click here)

Michael Young, senior director – Product Management, RMS

Hurricane Harvey is now driving catastrophic flooding across the entire Houston Metropolitan region. The behavior of the storm is almost without precedent, and Harvey has already broken all U.S. records for tropical cyclone-driven extreme rainfall with observed cumulative amounts of 51 inches (129 centimeters) – far exceeding Allison in 2001, along with Claudette in 1979, and Amelia in 1978, not only in volume but also regional extent.

While we will continue to refine our modeling parameters for the Category 4 wind and storm surge that Harvey generated on Saturday, our clear focus is now on the inundation of Houston, the fourth largest city in the U.S. The storm has achieved a paradigm shift, and we have mobilized all our capabilities to apply the tools, data and processes developed for the RMS U.S. High Definition (HD) Flood Model to provide insights to the extent and severity of the flooding, with Houston as our top priority.

RMS modelers have run the new RMS U.S. HD Flood Model in real time to simulate the precipitation, run-off, and pluvial and fluvial flows across the Houston domain to support a pipeline of flood deliverables for our clients. The model estimates that the economic loss from this event could be as high as US$70-$90 billion in total from wind, storm surge and inland flood. The estimate for wind and storm surge continues to be very modest within this total, with analysis of our preliminary event recreations suggesting than less than 10 percent of this economic loss will be driven by wind and storm surge damage to property and offshore platforms.

This estimate includes damage to all residential, commercial, industrial, and automotive risks in the area, as well as possible inflation from area-wide demand surge. It is worth noting that these wind and storm surge losses are very modest for a U.S. landfalling Category 4 hurricane, due to the fact that the most intense winds did not directly impact the most populated areas.

The figure below shows a high-fidelity hazard inundation map resulting from this effort, and this map has been provided to RMS clients. This map is based on the total forecast rainfall amounts – now estimated to be up to 55 inches in some areas – and shows, on a street-by-street basis, vast tracks of land that are may be covered in water at some point during the event.

Figure 1. RMS modeled flood inundation in south Texas, based on rainfall forecast totals out to August 31

Unlike Harvey’s wind footprint, which did not affect the most highly populated coastal areas, Harvey’s flood footprint sits squarely over Houston. The exposed value is indeed vast – there are over seven million properties with over $1.5 trillion in value in the Houston area. This is almost 10 times more exposed value, in today’s prices, than what was affected by Hurricane Katrina some 12 years ago.

Our models project that the overall economic loss will be US$70-$90 billion. The majority of these losses will be uninsured given that private flood insurance is limited. However, the insured losses will be significant, yet will remain uncertain for some time as private coverage is not consistent, with significant variations in how coverage is provided by individual insurers.

Coverage for some of the residential losses has been provided by the National Flood Insurance Program (NFIP). RMS estimates that approximately 500,000 NFIP policies will be affected by Harvey, and the losses to the program will be very significant – potentially the largest event to date. However, NFIP penetration rates are as low as 20 percent in the Houston area, and thus most of the losses will be uninsured which will rekindle the public policy debate around this issue.

RMS will continue to model the event as it continues to unfold, including updates to our economic loss estimates in the coming week.

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