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DISASTER 101 – FLOODING

When most people think of natural disasters, the first thing to come to mind is not likely flooding. However, flooding is the most common natural disaster. Flooding occurs in all 50 states, accounts for 40% of natural disasters, averages 5 billion dollars in damage each year, and claimed an average of 75 lives per year over the last 30 years.

Worldwide, statistics are similar.

According to the 30 year average, flooding is responsible for the most weather-related fatalities.

TYPES OF FLOODING

River and Lake Flooding

River and lake flooding is probably what most people envision when they think of floods. Heavy rainfall or snowmelt can cause water levels to rise overflowing banks and levees. River flooding is common in the Midwest as rain and snowmelt swells the tributaries that feed into larger rivers downstream. Once the water level crests the river banks, the area that is inundated can be widespread. Low lying areas, saturated soils, and urban areas can further exacerbate the effects of the overflow and take days to dissipate.

California experienced flooding in February when a weekend of storms increased runoff from Anderson Lake and flooded low-lying areas of San Jose. The early year storms also prompted the evacuation of over 88,000 people near the weakened Oroville Dam.

In May of 2017, heavy rainfall over the Midwest caused widespread flooding. Nearly 15 inches of rain fell over multiple states, saturating soils, and swelling multiple rivers above historic levels. Numerous levees were breached which flooded towns causing an estimated $1.7 billion dollars in damages to homes, businesses, and infrastructure.

40% of all natural disasters are flooding.

Coast Guard overflight of South Carolina flooding

Coastal Flooding and Storm Surge

A form of flooding happens regularly along coastlines due to the cycle of rising and lowering tides. Tides are a regular rise and fall of sea level caused by the gravitational interplay of the sun, moon, and earth. Occasionally, these tides can be exceptionally high. An increase of just a few feet is more than enough for tides to breech natural and man-made barriers. Many coastal cities are very near, or in some cases lower than, sea level making them especially prone to any change in sea level.

Storm surge can also cause extreme coastal flooding. The surge develops during severe weather, hurricanes, and tropical storms raising sea level as much as 25 feet. Sea level rise is the result of the low atmospheric pressure found in these storms which has a similar effect on sea level rise as the gravitational pull on tides. High winds common with these storms also cause large waves to batter the coast and push water farther inland. In worst case scenarios, the storm surge strikes the coast during a high tide cycle, increasing the flooding exponentially. Storm surge flooding is responsible for 90% of hurricane related deaths and the majority of the damage to structures.

In August of 2017, Hurricane Harvey alone caused over $125 billion dollars in damage and killed 89 people. The majority of the devastation caused by Harvey was a direct result of the widespread flooding of the Houston area.

Flash Floods

Flash floods can result from a variety of causes, but the common denominator is that they develop quickly and are normally caused by heavy rainfall. These floods can also be the result of snow melt, dislodged ice, inadequate urban drainage, or dam breaks. The actual volume of water carried in a flash flood is usually less than other flood types but the water is channeled down confined spaces which causes it to move with devastating force and speed. Because of this speed, flash floods are very dangerous, easily carrying mud, rocks, and trees in its flow. A Weather Channel article stated that, “water flowing at 7 mph has the equivalent force per unit area as air blowing at EF-5 tornado wind speed.” Whereas, “water moving at 25 mph has the pressure equivalent of wind blowing at 790 mph, faster than the speed of sound.”

 

BASIC SAFETY AND PREPAREDNESS

Ready.gov provides many helpful tips.

Be Mindful

  • Stay tuned to phone alerts, TV, or radio for weather updates, emergency instructions, or evacuation orders.
  • Avoid walking or driving through flood waters. 6 inches of moving water can knock a person over, and one foot of moving water can sweep a vehicle away. According to the Environmental Protection Agency, the leading cause of flood-related injury and death is individuals attempting to drive through flood waters.
  • Do not drive over bridges that are over fast-moving floodwaters. Floodwaters can scour foundation material from around the footings and make the bridge unstable.
  • If there is a chance of flash flooding, move immediately to higher ground.

Protect your home

  • Know your flood risk, avoid building in flood plains, and consider buying flood insurance.
  • If you have to evacuate due to flooding, and if safety permits, turn off all the utilities to your home and attempt to move valuables to the highest possible level.

SOURCES

https://www.ready.gov/floods
https://www.nssl.noaa.gov/education/svrwx101/floods/types/
https://www.ncdc.noaa.gov/billions/events/US/2017-2018
http://www.floodsite.net/juniorfloodsite/html/en/student/thingstoknow/hydrology/floodtypes.html
https://weatherology.com/articles/106/The+Dangers+of+Flash+Floods.html
https://weather.com/storms/severe/news/power-flood-water-20130704
https://www.livescience.com/23913-flood-facts.html

bark beetle tree

California Tree Mortality At An Unprecedented Level

Tree Mortality Overview

According to U.S. Forest Service study done in the summer of 2017, about 6.3 billion dead trees are still standing in 11 Western states, an increase of half a billion from five years ago. 103 million trees have died in California alone since 2010. So what’s happening to the trees? Well, established trees are normally fairly resilient to seasonal changes in their environment, but the last five years of drought in CA coupled with climate change impacts have imposed several stressors acting on the trees at the same time. Most native California trees are fairly resilient to drought, but a prolonged drought weakens the trees and exposes them to pests and disease that a healthier tree could normally fight off. A recent story by the CBS San Francisco discussed the situation in the Sierra National Forest with two Forestry experts there. They stated that there are more dead trees than live ones and will be dealing with the tree mortality there for many years to come.

Tree Mortality Danger

When a tree dies, its wood dries out and becomes very flammable.  When building a campfire, there’s a reason we use downed wood instead of chopping down live trees. Healthy, living trees have a relatively high moisture content.  This helps trees survive a wildfire and slows the progress of that wildfire. When tree death occurs from old age or other reasons, standing dead or fallen trees provide a large amount of dry fuel for wildfires, encouraging fire growth and hindering efforts to put it out. Not only are decomposing trees more flammable, they can also present a safety hazard to firefighters. Specifically, dead trees can fall during fires (which have resulted in deaths), and fallen trees can be an obstacle preventing vehicles and firefighters from reaching or escaping a wildfire.

bark beetle-caused tree mortality

Bark Beetle impact from 2012 US Forest Service report

What’s Happening to the Trees?

Established trees are fairly resilient to seasonal changes in their environment, so it is difficult to understand exactly what is causing so much tree death in California. Perhaps not surprisingly, several stressors have been acting on the trees at the same time.

Drought:

California saw a five-year historic drought that only just ended this last year. Most native California trees are fairly resilient to drought, but this prolonged drought weakened the trees and made them more susceptible to beetles and disease. Two deadly invaders that a healthier tree could normally fight off.

tree mortality in Julian

Tree death (brown trees) near Julian in San Diego County

Pests:

Tree bark is the main defense for trees against pests, disease, and fires. Bark beetles burrow into the bark and expose the trees to other pests or diseases, and can reduce their fire resiliency. Different types of bark beetles act as pests to different types of trees. The Pines and Conifers in the Sierra Nevada Mountains have been decimated by these beetles. Beetle-kill trees have been blamed for prolonging the firefight on the Beaver Creek Fire in Northern Colorado and also the Cedar Fire in California’s Southern Sierra Nevada Range. Tree deaths due to these beetles have been attributed to several major campaign fires across the west over the past few summers. The map above shows hard-hit beetle kill timber forests across the west (in red), which includes both the Cedar and Beaver Creek fire areas.

Disease:

The coast live oak trees have been exposed to Sudden Oak Death, which is caused by a non-native tree fungus. This fungus and other non-native diseases are responsible for an estimated 5 – 10 million oak tree deaths. Many dead trees were identified in the areas where the Soberanes fire near Big Sur is currently burning and have likely contributed (along with major drought) to its acreage eclipsing 100,000 this week.

Plans for Tree Death Prevention

Drought, pests, and disease all put stress on otherwise healthy trees.  When these stresses are combined, we can expect to see continued tree death at unprecedented scales. California has programs to both reduce the amount of tree death and to remove dead trees as a means of reducing fire danger.  Lately, resources have been too scarce to keep up with the levels of tree deaths plaguing the state. Learn more about the epidemic and what is being done to prevent further problems here.


Sources:

www.fs.fed.us

www.fire.ca.gov

www.yale.edu

The Denver Post

Editor’s Note: This article was originally published in September 2016 and was updated in September 2017

Tree Death Fuels California Wildfires

Tree Death Adds Fuel to the Fire

A record 66 million trees have died in California since 2010, adding a huge fuel threat to an already dangerous fire landscape.  Not only are decomposing trees more flammable, they can also present a safety hazard to firefighters. Specifically, dead trees can fall during fires (which have resulted in deaths), and fallen trees can be an obstacle preventing vehicles and firefighters from reaching the fire.

Dead Wood Danger

When a tree dies, its wood dries out and becomes very flammable.  When building a campfire, there’s a reason we use downed wood instead of chopping down live trees. Healthy, living trees have a relatively high moisture content.  This helps trees survive a wildfire and slows the progress of that wildfire. When tree death occurs from old age or other reasons, standing dead or fallen trees provide a large amount of dry fuel for wildfires, encouraging fire growth and hindering efforts to put it out.

Bark Beetle impact from 2012 US Forest Service report

Bark Beetle impact from 2012 US Forest Service report

What’s Happening to the Trees?

Established trees are fairly resilient to seasonal changes in their environment, so it is difficult to understand exactly what is causing so much tree death in California. Perhaps not surprisingly, several stressors have been acting on the trees at the same time.

 

Drought:

California has been in an historic drought for the past five years. Most native California trees are fairly resilient to drought, but a prolonged drought weakens the trees and exposes them to pests and disease that a healthier tree could normally fight off.

Tree death (brown trees) near Julian in San Diego County

Tree death (brown trees) near Julian in San Diego County

Pests:

Tree bark is the main defense for trees against pests, disease, and fires. Bark beetles burrow into the bark and expose the trees to other pests or diseases, and can reduce their fire resiliency. Different types of bark beetles act as pests to different types of trees. The Pines and Conifers in the Sierra Nevada Mountains have been decimated by these beetles. Beetle-kill trees have been blamed for prolonging the firefight on the Beaver Creek Fire in Northern Colorado and also the Cedar Fire in California’s Southern Sierra Nevada Range. Tree deaths due to these beetles have been attributed to several major campaign fires across the west over the past few summers. The map above shows hard-hit beetle kill timber forests across the west (in red), which includes both the Cedar and Beaver Creek fire areas.

Disease:

The coast live oak trees have been exposed to Sudden Oak Death, which is caused by a non-native tree fungus. This fungus and other non-native diseases are responsible for an estimated 5 – 10 million oak tree deaths. Many dead trees were identified in the areas where the Soberanes fire near Big Sur is currently burning and have likely contributed (along with major drought) to its acreage eclipsing 100,000 this week.

Plans for Tree Death Prevention

Drought, pests, and disease all put stress on otherwise healthy trees.  When these stresses are combined, we can expect to see continued tree death at unprecedented scales. California has programs to both reduce the amount of tree death and to remove dead trees as a means of reducing fire danger.  Lately, resources have been too scarce to keep up with the levels of tree deaths plaguing the state. Learn more about the epidemic and what is being done to prevent further problems here.


Sources:

www.fs.fed.us

www.fire.ca.gov