Natural Threats & Hazards
These events are emergencies caused by forces extraneous to man in elements of the natural environment. Natural hazards are often interrelated. For example, flash flooding often occurs in areas burnt by wildland fires because there is less vegetation to slow the flow of water.
Unlike other parts of the country, thunderstorm wind gusts here in the Southwest almost always exceed 40 mph. The strongest wind gusts can exceed 100 mph, and can produce damage similar to a tornado!
STRAIGHT-LINE WIND is a term used to define any thunderstorm wind that is not associated with rotation, and is used mainly to differentiate from tornadic winds. Straight-line winds can travel dozens of miles away from the thunderstorm that produced them.
A DOWNBURST is a strong downdraft resulting in an outward burst of damaging straight-line winds on or near the ground, sometimes producing damage similar to a strong tornado.
TORNADOES do occur in Arizona. Unfortunately, many of them here are not detectable by radar because they are either too small, hidden by interfering mountains, or develop from the ground up. While they do not last long, they can occur with little or no warning, and can do considerable damage.
More information on Damaging Winds
Drought creates environmental conditions that increase the risk of other hazards such as wildfire, flash flood, landslides and debris flow. Drought is a result of a natural decline in the expected precipitation over an extended period of time, typically one or more seasons in length. A drought’s severity depends on numerous factors, including duration, intensity, and geographic extent as well as regional water supply demands. While the Sonoran Desert’s arid climate has subjected Maricopa County to drought conditions throughout its history, water management efforts have mitigated water shortages for the past century.
More information on Drought
Thunderstorms frequently produce downbursts, straight line winds, and tornadoes. All three of these wind types can create dust storms or “haboobs". Dust Storms are unexpected, unpredictable and can sweep across desert landscapes at any time. During an average year, generally one to three dust storms will move into the Phoenix area, usually lasting a few minutes to an hour. They often come with no warning and can significantly reduce visibility, resulting in deadly multi-vehicle accidents on roadways. You can endure these brief but powerful windstorms if you know how to react.
More information on Severe Wind and Dust Storms
Maricopa County frequently exceeds temperatures of 110 degrees Fahrenheit in the summer months, but is fortunate enough to have relatively low humidity. Extreme Heat can cause serious or even fatal medical conditions. Common hazards associated with extreme heat include heat cramps, heat syncope, heat exhaustion, and heat stroke.
The National Weather Service is using Heat Risk as a determining factor for watches and warnings. Heat Risk considers factors such as location, time of year, and duration to assess Heat Risk.
More Information on Extreme Heat
Extreme Heat Resources
Three types of storms trigger flooding in Maricopa County: tropical storm remnants, winter rains, and summer monsoons.
LOCALIZED FLOODING is a result of excessive precipitation/storm runoff over a short period of time. In addition to heavy rain; poorly designed, maintained, altered, or blocked control measures often contribute to these localized floods.
FLASH FLOODS result from storm runoff from local or distant mountainous areas moving quickly through normally dry washes and riverbeds. These common types of floods are fast moving and often short lived.
More Information on Flooding and Flood Insurance
Maricopa County is particularly susceptible to land subsidence and earth fissures. SUBSIDENCE is the gradual sinking of land that eventually forms a bowl shape. An EARTH FISSURE is a crack in the earth’s surface associated with land subsidence. Both result from the removal or depletion of underground fluids, such as groundwater, or from the excessive use of surface water. Both can cause drainage problems, breach canals, and alter flood patterns or flood control measures. They can also damage underground utilities, infrastructure, roadways, and building foundations.
In areas burned by forest and brush fires, a lower threshold of precipitation may initiate landslides. In a LANDSLIDE masses of rock, earth and/or debris move down a slope. DEBRIS and MUD FLOWS are rivers of rock, earth, and other debris saturated with water. All can be caused by a variety of factors, including earthquakes, heavy rainfall, volcanic eruptions, fire, and by land mismanagement, particularly in mountain, canyon, and coastal regions.
All 50 states are at some risk of EARTHQUAKES. Large earthquakes in Arizona are rare, but not unheard of. Since 1850, Arizona has had more than 20 earthquakes with magnitudes of 5.0 or higher. The U.S. Geological Survey reports that the largest earthquake on record in Arizona measured 5.6 in July 1959. Maricopa County rarely has earthquakes, but they do happen. Often quakes in other counties are felt here, like the 2015 quake in Yavapai County near Black Canyon City. Three earthquakes from magnitudes 3.2 to 4.1 were felt 45 miles away in Phoenix.
More Information on Subsidence and Earth Fissures
More Information on Landslides
More Information on Earthquakes
Monsoon Season is the most dangerous time of year weather-wise in the Southwest. Although the Monsoon brings welcome rains and relief from the summer heat, the thunderstorms that come with the Monsoon bring their own hazards. Lightning, severe wind, dust storms, and flooding can all accompany thunderstorms, causing injuries and property damage.
More information on Monsoon Storms
Wildfires often begin unnoticed but quickly spread and produce a noticeable dense smoke that can be seen for miles. Although many in the valley live in urban areas, other areas have what is called a “Wildland Urban Interface”, which creates an environment where fire can move readily between structures and vegetation. Residential and commercial expansion into these areas can increase the likelihood that wildfires may threaten structures and people, and are both dangerous and costly to fight.
Wildfires can be started by nature through lightning strikes and dry, hot weather conditions, but can also be human-caused by accident, carelessness or criminal intent. Maricopa County’s summer high temperatures and dry climate provide a combustible environment for all of these ignition methods. The lingering effects of a wildfire may include soil erosion, landslides, and reduced food for the local animal population.
More Information on Wildfires