Browsing by Subject "Tropical Cyclone"
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Item Investigation of Variations and Impacts of Tropical Cyclone Precipitation in Texas (1950-2009)(2013-07-30) Zhu, LaiyinThis dissertation examines the causes of variations in tropical cyclone precipitation (TCP) and the relationship between TCP and river discharge in Texas. The dissertation has three major objectives: 1) investigate the spatial and temporal variations of TCP in Texas from 1950 to 2009, 2) construct seasonal statistical forecast models for TCP and identify the primary factors controlling TCP in Texas, and 3) examine how TCP contributes to the extreme precipitation and river discharge in watersheds surrounding the city of Houston. An automated extraction method is developed to identify TCP from 60 years of precipitation data from Cooperative Observing Network gauges. Texas receives an average of 123.5 mm of TCP/year, which is ~13% of the state?s mean annual precipitation. September is the month with the most TCP, and it receives an average of 18.5 mm. Long-term trends (>50 years) in TCP are evident at some locations, but there are no statistically significant long-term trends in aggregated annual TCP metrics. Despite the lack of long-term trends, TCP metrics show some spectral power at periodicities of ~2-3 years, ~5-8 years, and >10 years. Areas within 400 km of the coast have higher risk of extreme daily TCP (>100 mm), but inland Texas can also occasionally experience extreme TCP. In some areas in southeastern Texas the probability of receiving >100 mm of daily TCP in any given year is ~0.30 (i.e., daily TCP exceeds 100 mm, on average, 1 out every 3 years). The best seasonal forecast models of TCP can explain >20% variance based on three or fewer predictors. ENSO is the most important control of TCP in Texas. La Ni?a, the major driver in all TCP models, reduces the vertical wind shear in the Caribbean and tropical Atlantic and therefore generates more precipitating storms in Texas. Maximum Potential Velocity (MPV) in the Gulf of Mexico and vorticity in the Atlantic Hurricane Development Region (MDR) are also important predictors of TCP and they can increase the R2 by ~0.2. The negative relationship between MPV and vorticity with the TCP are due to the fact that TCs with weaker wind speed and slower translation speed tend to contribute much more to both extreme and total TCP. Sea level pressure in the Gulf of Mexico, SST in the Caribbean and North Atlantic Oscillation are also identified as useful predictors in some of the models. TCP is associated with many of the annual maximum discharge events in watersheds near Houston. Urbanization can significantly increase river discharge generated by TCP. Both the annual maximum discharge and 90 percentile discharge have increased significantly in many watersheds in Houston. Although no long-term trend can be observed in the TCP and TCP-related extreme discharge, there may be an increased risk of floods from TCP because of the statistically significant increases in annual maximum discharge that have been observed. There are also increased uncertainties in flood risk because extreme precipitation, including TCP, is projected to become more variable in the future.Item The Impact of Tropical Cyclones on the Geomorphic Evolution of Bolivar Peninsula, TX(2012-07-16) Hales, BillyAnnually, tropical cyclones do tremendous damage and are agents of long-term coastal change. To test this idea of different tropical cyclones delivering consistent coastal change, a landform with such evolution is needed. One such landform is a spit. What contributions do tropical cyclones give toward the evolution of a spit, and do tropical cyclones give the same kinds of impacts? To determine if tropical cyclones have similar impacts, shoreline and volumetric change from four storms impacting Bolivar Peninsula are considered. Being a southwest-trended spit at a length of 33.5 kilometers, storm impacts are measured in the form of one dimensional shoreline and two dimensional volumetric change. These impacts are abstracted into shoreline change and volumetric change patterns. These patterns are identified and compared for differences between each storm and similarity among all storms. Results indicate that shoreline accretionary zones vary alongshore. Results from Hurricane Ike indicate an accretionary zone ten kilometers from the distal end. Shoreline change patterns for Hurricane Rita show an unstable accretionary zone at four kilometers from the distal end. Results for Tropical Storm Fay indicate an unstable accretionary zone that begins at the distal end and continues to the middle of the spit. In terms of similarity for shoreline change, all patterns from storms demonstrated erosion near Rollover Fish Pass. One dimensional volumetric change patterns were entirely erosive for Hurricanes Rita and Ike, and Tropical Storm Fay had by small zones of accretion near the distal portion of the spit. Tropical Storm Josephine demonstrated an accretion zone between the middle and distal portion of the spit. Results from two dimensional volumetric change patterns suggest a threshold for inland penetration. Tropical Storm Fay showed a ten to twenty meter wide pattern of erosion around five kilometers from the distal end and near the proximal end of the spit, and Hurricane Rita demonstrated a twenty meter wide pattern of erosion near the distal end. Hurricane Ike had erosive penetration of up to 200 meters around fifteen kilometers from the distal end. Results suggest that certain storms reinforce the standard spit growth model, and others work against it.