Dam failures, floods, landslides

Laura

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FOTCM Member
I've been watching a few recent flood videos on the weather site I frequent and it strikes me that flooding is really seriously catastrophic even if it comes due only to a lot of rain and no particularly devastating storms or other activity. There are so many cities and communities built on waterways, and so many floods of late, it just feels like the planet is trying to wash itself.
 

c.a.

The Living Force
FOTCM Member
3 May 2019
The global mean sea level currently measures 77 millimeters higher than in 1993 when the satellite sea level record began. According to the Fifth Assessment Report from the United Nations’ Intergovernmental Panel on Climate Change, the global mean sea level is expected to continue rising throughout the 21st century. With 126 million Americans—40% of the total population of the United States—living along the coasts, rising seas could cause widespread property and socioeconomic damage in the coming century.

Coastal communities require adaptation and mitigation strategies for both frequent, minor flooding and extreme, high-water events (i.e., major flooding). Yet community responses differ for each type of flooding: Regular low-grade floods inflict chronic, cumulative damages, whereas extreme floods create substantial, acute losses. One challenge of strategic planning is that many statistical models struggle to simultaneously characterize both minor and major flood events resulting from rising sea levels.

To address this challenge, Ghanbari et al. developed a new model to facilitate a nonstationary analysis of coastal flood frequency. The mixture probability model simultaneously evaluates minor and major flooding under higher sea levels. The study incorporated data from 68 tidal monitoring locations around the country to estimate the type and frequency of flooding throughout the contiguous United States for both the present and future. The study also reports on flood exposure for 20 coastal cities.

The authors found that, generally, flood return periods shorten as sea level rises. For example, if sea levels climb by 15.24 centimeters, a 500-year flood will become a 10-year flood along the Pacific coasts. Throughout the country, coastal regions will experience increases in minor and major flood frequency if sea levels continue to rise. If sea levels rise by approximately 61 centimeters, the authors report that the majority of coastal communities will experience major floods multiple times (2–6 days) and more than 150 days of minor flooding per year, unless adaptation and mitigation strategies are adopted to increase flood thresholds in coastal cities.

The study found that not all regions would flood similarly in response to higher sea levels. The Pacific coast would see the most significant amplification in major flood frequency, followed by the southeast Atlantic coastline. The Gulf of Mexico and northeast Atlantic regions, however, would experience more frequency amplification in minor floods. Of the 20 cities the study assessed, the authors found that New York City would experience the highest increase in both minor and major flooding; Miami had the second-highest exposure.

The study represents a new approach for assessing flood risks associated with sea level rise and highlights the importance of planning for both chronic and acute flooding. The results offer actionable information to decision-makers in coastal communities throughout the United States. (Earth’s Future, https://doi.org/10.1029/2018EF001089, 2019)
—Aaron Sidder, Freelance Writer
Mississippi River to remain out of its banks into at least mid-June in Louisiana
May 11, 2019 6-7 minute read Snip:
Parts of the south-central United States hammered by severe weather and flash flooding this week will face long-term river flooding through the rest of May and even into June.

Southeastern Texas, including the Houston area, was hit hard by a couple rounds of flooding downpours, damaging winds and large hail this week. Ten inches of rain fell in Sugar Land, Texas, on Tuesday alone.

One more round of drenching thunderstorms and torrential downpours will target areas from eastern Texas to the lower Mississippi Valley through Saturday night before dry weather finally returns for Sunday and Monday. Another dry spell is expected later in the new week.



Even with the return of dry weather, the flooding on the Mississippi River will continue to get worse into the middle to latter portion of the month.

“River flooding may continue into June as floodwaters in rivers farther north travel southward and add onto the ongoing flooding along the lower Mississippi River,” AccuWeather Meteorologist Brett Rathbun said.

Rathbun added that rain and thunderstorms may return by Tuesday and Wednesday of next week, and that any additional rainfall during the rest of May will only make the flooding situation worse.

Moderate to major flooding is already occurring along nearly the entire length of the Mississippi River from the Iowa/Illinois border to west of New Orleans, Louisiana.

In addition, flooding is taking place along the Missouri, Sabine, Wabash and White rivers, as well as other creeks and streams in the central and southern United States.



 
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