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Impacts of Hurricanes

Hurricanes and tropical storms can cause major damage and loss of life due to the heavy rains, strong winds, and storm surge. Hurricanes are among the most important and devastating natural disasters. The two most common measures of hurricane impact are deaths and economic loss. Death tolls from extreme hurricanes can be staggering – over 20,000 lives were lost in the 1780 Antilles hurricane, perhaps as many in 400,000 died as a result of 1970’s Bohla cyclone in Bangladesh, and more than 10,000 perished during 1998’s Hurricane Mitch [1],[2]. While the largest single-event death tolls in the recorded history of natural hazards are attributable to epidemics, famine, floods and droughts [3], more deaths are attributable globally to hurricanes in an average year than any other natural hazard [4]. For North America and the Caribbean, Rappaport and Fernández-Partagás [2] estimate as many as 500,000 deaths may be attributable to hurricanes since European contact in 1492, including the loss of over 20,000 in the 1780 Antilles storm, 10,000 as a result of 1974’s hurricane Fifi in Honduras, and 8,000 to 12,000 during the 1900 storm in Galveston, Texas.

Storm Surge

Among the most damaging features of a hurricane is its storm surge. In areas prone to large surge, wind surge is the main component. But, ocean level rise due to pressure drop, waves breaking at the shore, and strong currents also contribute to surge. By definition, "storm surge" is the vertical water elevation above normal levels. While, "flood elevation" (sometimes called "storm tide") is the vertical water elevation above some datum, for example above mean sea level. So, flood elevation includes both storm surge and normal tide level.

Definition of storm surge and flood elevation.Definition of storm surge and flood elevation.
Flooding near Galveston, TX during Hurricane Ike in 2008 (photo courtesy of C. Parrish, U.S. Airforce).Flooding near Galveston, TX during Hurricane Ike in 2008 (photo courtesy of C. Parrish, U.S. Airforce).

What Impacts Surge Magnitude?

Hurricanes can be described in terms of their intensity, size, speed, and landfall location. Of these, intensity, size, and landfall location most influence surge magnitude along continuous coasts. Hurricane intensity is typically defined as the hurricane's maximum wind speed, or Category. But, hurricane central pressure better indicates surge potential [5]. The figure below shows that:

  1. Surge increases with increasing intensity.
  2. Surge increases with increasing size.
  3. Surge is larger when landfall is over a wider continental shelf.
Definition of storm surge and flood elevation.Definition of storm surge and flood elevation.

Why Are Surges Usually Higher on the Upper Texas Coast?

In Texas, the continental shelf changes dramatically. To the south, the shelf is narrow. To the north, the shelf is much wider. Because wind surge is only generated in shallow waters, larger surge may be generated when the continental shelf is wider. As an illustration, in 2008 Hurricane Ike, a very large Category 2 storm, made landfall in Galveston, TX. Highest recorded surges were on the order of 5 m (16 ft). The figure below shows what the surge would have been if Ike had taken a different path. If Ike had hit along the lower Texas coast, the surge would have been half as high.

PeakEstimated peak surge if Hurricane Ike made landfall instead at the location shown. Values are shown as percent of the peak historical surge. Actual landfall location for Hurricane Ike is shown as a black diamond. Dashed line is 30-m depth contour—a measure of continental shelf width. Surge values estimated using Irish and Resio [6].

Waves

Hurricanes bring with them large, destructive waves. Hurricane waves at the coast are generated by hurricane winds. Some waves, called "swell," are created while the hurricane is offshore. These waves then travel the ocean to reach the coast. Other waves, called "wind seas," are created at the coast while the hurricane makes landfall. The primary difference between wind seas and swell is that more time passes between each consecutive swell wave. High surge allows large waves to move further inshore, bringing their destructive power to homes and other structures onshore. Large coastal waves have very high velocities that are much more destructive than the velocities associated with surge alone.

Waves breaking at the shore during Hurricane Ike in 2008 (photo courtesy of P.M. Johnson).Waves breaking at the shore during Hurricane Ike in 2008 (photo courtesy of P.M. Johnson).

What Impacts the Size of Hurricane Waves?

The size of hurricane waves increase with increasing hurricane intensity, size, and speed (e.g., Alves et al., 2004 [7]). When waves approach the shore, they interact with the sea bottom. This interaction causes the waves to first increase in size, until the depth becomes too shallow and the wave "breaks." During breaking, waves decrease in size. Waves will also break against structures, like the Galveston seawall, a house, or a pier.

Hurricane waves tend to be smaller in areas protected from the ocean. For example, large ocean swell may not be able to move all the way into a coastal bay like Galveston or Corpus Christi Bay.

Large ocean waves at Huntington Beach, California do not propagate into bay area (photo B. Perry).Large ocean waves at Huntington Beach, California do not propagate into bay area (photo B. Perry).

Hurricane Wind Damage

Billions of dollars in damages have been caused by hurricane winds [8],[9],[10]. Although the number of deaths (compared to storms such as the Galveston hurricane of 1900) has significantly dropped, wind damage greatly affects structures [10]. Approximately 16% of wind related deaths between 1970 and 1999 were caused by hurricanes [10]. In comparison, drowning (some caused by storm surge) caused 82% of deaths for the same time period [10].

Precipitation

Tropical Cyclones (TCs) frequently produce extreme precipitation. TC precipitation (TCP) accounts for a considerable portion of both total annual precipitation and extreme precipitation along the Atlantic and Gulf of Mexico coasts in United States [11],[12],[13]. TCP causes inland flooding that can result in significant economic damage and loss of life [14],[15].

At a larger scale, there is an increasing trend in North Atlantics TCs’ contribution to both annual total rainfall and extreme rainfall events (i.e., top 5% of rainfall events) from 1979 to 2005 [16]. Kunkel et al. [13] reported that TCrelated extreme precipitation events in the eastern U.S. doubled during 1994-2008 as compared to the long-term (1895-2008) average. Knight and Davis [12] also showed that the TCP contribution to extreme precipitation increased during 1972 to 2007 due to increases in both storm frequency and intensity. Nogueica and Keim [17] found increasing trends in both annual TCP volume and affected area in the eastern U.S. since 1995, which are attributed to increases in TC frequency. Generally, these large-scale studies show increases in TCP in recent years, both in terms of extreme precipitation and the contribution to annual precipitation. Increases in TC frequency are responsible for much of this trend. However, there is no evidence of an increase in TC-related precipitation in Texas (based on 1950-2009) [18].

Generally, the front half and right side of the TC receive more frequent and intense precipitation than the rear half and the left side. The largest TCP events in Texas are associated with slow moving or stalled TC systems.

Spatial distribution of monthly TC precipitation (mm)(1950-2009) a. June, b. July, c. August, d. September, e. October (created by Zhu and QuiringSpatial distribution of monthly TC precipitation (mm)(1950-2009) a. June, b. July, c. August, d. September, e. October (created by Zhu and Quiring [18]).

What impacts precipitation and inland flooding?

Tropical cyclones (TC) are one of the primary causes of severe riverine flooding in Texas [19],[20]. Many of the recent TCs with more than a billion dollars in losses have made landfall near Houston (e.g., Tropical Storm Allison, Hurricane Rita, and Hurricane Ike) (http://www.ncdc.noaa.gov/billions/).

Riverine flooding is a hazard that causes major destruction and loss of life in the United States [21]. Texas is a state that has been frequently influenced by severe riverine flooding [19],[22]. The rapid urbanization in this region has also increased its vulnerability to riverine floods [23],[24]. Past studies about TC precipitation and flooding have focused on the historical patterns and trends in extreme precipitation and discharge for all of Texas [19],[25] or have focused on just one watershed [23]. Although the Houston area is frequently influenced by TCs [18], few studies have examined the impact of tropical cyclone precipitation (TCP) on discharge and flooding in watersheds near Houston. 

Many TC systems travel towards the north and west after landfall. Typically TCP intensity gradually decreases as the TC moves inland. However, sometimes TC re-intensify because of interactions with other weather systems or local conditions. These inland TCP events can generate large amounts of precipitation in western and northern Texas, such as the >500 mm/day of TCP that fell in western Texas from Hurricane Alice (1981), or the clusters of TCP extremes (~250 mm/day) in northern Texas associated with TS Dean (1995) and TS Erin (2007). Antecedent soil moisture conditions are one of the factors that led to the re-intensification of TS Erin (2007) [26].

In other cases inland TCP maxima are associated with TCs that become stalled due to weak steering winds or interactions with mid-latitude weather systems (TS Claudette in 1979 and TS Delia in 1973). Other TCs that generated extreme amount of precipitation did so because they reversed course (TS Alison in 2001 and Hurricane Beulah in 1967). TS Claudette and TS Alison are associated with the record daily TCP in Texas (~1000 mm) and the heavy precipitation and slow movement caused major inland flooding.

The 10 hurricanes/tropical storms that have caused the most precipitation in Texas (between 1950-2009) (created by Zhu and QuiringThe 10 hurricanes/tropical storms that have caused the most precipitation in Texas (between 1950-2009) (created by Zhu and Quiring [18]).

Reference

[1] Emanuel, K., Divine Wind: The History and Science of Hurricanes. Oxford University Press. 296. 2005.

[2] Rappaport, E.N. and J.s.J. Fernández-Partagás, History of the Deadliest Tropical Cyclones Since the Discovery of the New World, in Hurricanes: Climate and Socioeconomic impacts, H.F. Diaz and R.S. Pulwarty, Editors. Springer-Verlag: Berlin, Germany. p. 93-108. 1997.

[3] CRED. Emergency Events Database. Available from: http://www.emdat.be/index.html. 2008.

[4] Murnane, R.J., Introduction, in Hurricanes and Typhoons: Past, Present and Future, R.J. Murnane and L. Kam-Biu, Editors. Columbia University Press: New York. p. 1-10. 2004.

[5] Irish, J.L., and Resio, D.T., Reply to Discussion of ‘A hydrodynamics-based surge scale for hurricanes’, Ocean Eng., 37(11-12), 1085-1088, 2010a.

[6] Irish, J.L., and Resio, D.T., A hydrodynamics-based surge scale for hurricanes, Ocean Eng. [Special Issue, Interagency Performance Evaluation TaskForce (Hurricane Katrina), Z. Demerbilik, (ed.)], 37(1), 69-81, 2010b.

[7] Alves, J.H.G.M., Tolman, H.L., and Chao, Y.Y., Forecasting hurricane-generated wind waves at NOAA/NCEP, JCOMM Technical Report 29, WMO/TD-1319, 2004.

[8] Elsner, J.B. and A.B. Kara, Hurricanes of the North Atlantic: climate and society. New York: Oxford University Press. 488. 1999.

[9] Emanuel, K.A., Divine wind :the history and science of hurricanes. New York: Oxford University Press. 2005.

[10] Willoughby, H.E. and M.E. Rahn, Parametric Representation of the Primary Hurricane Vortex. Part I: Observations and Evaluation of the Holland (1980) Model. Monthly Weather Review, 132(12): p. 3033-3048. 2004.

[11] Knight, D. B., and R. E. Davis, Climatology of tropical cyclone rainfall in the southeastern United States, Phys. Geogr., 28(2), 126–147, 2007.

[12] Knight, D. B., and R. E. Davis, Contribution of tropical cyclones to extreme rainfall events in the southeastern United States, J. Geophys. Res. Atmos., 114, 2009.

[13] Kunkel, K. E., D. R. Easterling, D. A. R. Kristovich, B. Gleason, L. Stoecker, and R. Smith, Recent increases in U.S. heavy precipitation associated with tropical cyclones, Geophys. Res. Lett., 37, L24706, 2010.

[14] Pielke, R. A., M. W. Downton, and J. B. Miller, Flood damage in the United States, 1996–2000: a reanalysis of National Weather Service estimates, University Corporation for Atmospheric Research, Boulder, CO, USA. 2002.

[15] Rappaport, E. N., Loss of life in the United States associated with recent Atlantic tropical cyclones, Bull. Am. Meteorol. Soc., 81(9), 2065–2073, 2000.

[16] Lau, K. M., Y. P. Zhou, and H. T. Wu, Have tropical cyclones been feeding more extreme rainfall?, J. Geophys. Res. Atmos., 113(D23), 2008.

[17] Nogueira, R. C., and B. D. Keim, Annual Volume and Area Variations in Tropical Cyclone Rainfall over the Eastern United States, J. Climate, 23(16), 4363–4374, 2010.

[18] Zhu, L., and S. M. Quiring, Variations in tropical cyclone precipitation in Texas (1950 to 2009), J. Geophys. Res. Atmos., 118, 3085–3096, 2013.

[19] Villarini, G. and J.A. Smith, Flooding in Texas: Examination of Temporal Changes and Impacts of Tropical Cyclones. JAWRA Journal of the American Water Resources Association, 2013.

[20] Bradley, A.A. and J.A. Smith, The Hydrometeorological Environment of Extreme Rainstorms in the Southern Plains of the United States. Journal of Applied Meteorology, 33(12): p. 1418-1431.1994.

[21] Pielke, R.A. and M.W. Downton, Precipitation and damaging floods: Trends in the United States, 1932-97. Journal of Climate, 13(20): p. 3625-3637. 2000.

[22] Ashley, S.T. and W.S. Ashley, Flood fatalities in the United States. Journal of Applied Meteorology and Climatology, 47(3): p. 805-818. 2008.

[23] Olivera, F. and B.B. DeFee, Urbanization and its effect on runoff in the Whiteoak Bayou watershed, Texas. Journal of the American Water Resources Association, 43(1): p. 170-182. 2007.

[24] Brody, S.D., et al., A spatial-temporal analysis of section 404 wetland permitting in Texas and Florida: Thirteen years of impact along the coast. Wetlands, 28(1): p. 107-116. 2008.

[25] Smith, J.A., et al., Catastrophic rainfall and flooding in Texas. Journal of Hydrometeorology, 1(1): p. 5-25. 2000.

[26] Evans, C., Schumacher, R. S. and T. J. Galarneau, Sensitivity in the Overland Reintensification of Tropical Cyclone Erin (2007) to Near-Surface Soil Moisture Characteristics. Monthly Weather Review, 138: 3848-3870. 2011.

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