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Floods & Climate Change – What Do We Know?

How to Prepare for an Extreme Weather Disaster – Tips from a Preparedness Expert

With Climate Change, rising temperatures now produce more deadly extreme weather patterns. Get Ready Now! Check out the weather map on this page (it is interactive so you can move to another ocean area). Find out more about floods in your area from National Weather Service.

What and Where is a Flood?

A flood is basically an overflow of water onto land that is usually dry. That seems simple enough but the causes are not so simple. Floods can develop gradually over hours or days, or they can occur very quickly with little warning. The duration can also vary, lasting days, weeks, or even longer. There are two basic types of floods: flash floods and the more widespread river floods. Floods are the most common natural disaster around the world. They can cause major property damage, loss of life, and destroy livelihoods. And climate change has increased the risk of major flooding even for areas previously less susceptible to extreme weather events, such as the flooding in Vermont from the remnants of Hurricane Irene or the 2023 flooding that was not caused by a single weather phenomenon, but rather a combination leading to heavy rainfall. This resulted in rivers overflowing their banks and submerging much of the downtown area of the state capital as well as other cities and towns.

What we fear: The news images of massive storm surges sweeping away coastal homes, sudden flash floods turning highways into deadly torrents and desperate people rescued from the roof tops of their homes are what we most often see. Stories of children ripped from their parents’ arms by the ferocity of surging water are nightmares for many who live in areas that have experienced flooding. What can anyone do when a wall of water from the ocean comes ashore or a raging river reaches beyond its banks and the flood plain? And the thought of water slowly coming in our front door and then rising higher and higher on the ground floor as we scramble up the stairs knowing that nothing we do can keep the water out.

What we experience: Predicting floods can be a challenge. The National Weather Service (an agency within the National Oceanic Atmospheric Administration) collects and interprets rainfall data throughout the United States and issues flood watches and warnings. Click here to see the NOAA weather map. We heed the flood watch and flood warnings that come with approaching storms, but our ability to protect our homes and families varies according to the plans and capabilities of the entire community. Sometimes we try to anticipate rising waters with sandbags, cleared storm drains and other limited means, but once the deluge begins, we are often powerless to protect against the inevitable.

Puerto Rico flag remnants tied to wooden swings hanging over floodwaters covering a recreational area.
Hurricane Fiona roared over Puerto Rico on Sunday, Sept. 18, 2022, knocking out power to all of the U.S. territory. The storm brought up to 22 inches of rain, causing life-threatening floods. The blow from Fiona was made more devastating because Puerto Rico had yet to recover from Hurricane Maria, which killed nearly 3,000 people and destroyed the power grid in 2017.⁠ Puerto Rico’s shattered flags seen in a recreational area devastated by the Herrera River in Loíza, Puerto Rico, on Tuesday, Sept. 20, 2022. (Photo: Yadira Hernandez-Pico)

Americares has responded and remained in communities that have historically suffered the worst effects of flooding such as Puerto Rico or New Orleans and the Gulf Coast of the U.S., and we vigorously support preparedness efforts for the vulnerable health systems. Learn more about our work to support Client Resilient Health Clinics.

For decades at Americares, we have seen up close the staggering magnitude of extreme weather losses for families and communities – the personal history and common goods. Access to medicine security and to health services become early casualties as emergency responders rush to provide the basics of food, shelter, clean water and hygiene in the first days. We know that immediate access to primary health services, including mental health support, along with medicines and medical supplies will save lives and restore health. Working with local partners, governments and other nonprofits to meet immediate needs, we then help survivors rebuild health facilities and services and restore hope for the future. No matter where extreme weather disasters strike, we are there and together with our partners, even in the worst times, we can make health happen.

Learn more about health crises from Climate Change: Hurricanes. Extreme Heat. Wildfires.

What are the Causes of Floods?

Sources of the Threat

According to the US Geological Service (USGS), there are two basic types of floods: flash floods and the more widespread river floods. Flash floods generally cause greater loss of life and river floods generally cause greater loss of property. Often people are caught on roads in their cars or on foot during flash floods and when a river overflows its banks it quickly inundates homes and businesses. There is a third type (storm surge) primarily associated with Hurricanes.

Flash Floods: Runoff from excessive rainfall can cause a rapid rise in the water height (stage) of a stream or normally-dry channel. Flash floods are more common in areas with a dry climate and rocky terrain because lack of soil or vegetation allows torrential rains to flow overland rather than sink into the ground. It quickly gathers momentum and sweeps away whatever is in its path.

River flooding: It is generally more common for larger rivers in areas with a wetter climate, when excessive runoff from longer-lasting rainstorms and sometimes from melting snow causes a slower water-level rise over a larger area that can no longer absorb the water. Floods also can be caused by ice jams on a river or high tides, but most floods can be linked to a storm of some kind.

Storm Surges: Storm surge represents a third and increasingly more common source of sudden flooding. Coastal areas that have become more vulnerable to major hurricanes are experiencing the power of ocean water pushed by high winds and high tides as a literal wall of water that smashes onto land with devastating force. The storm surge combined with the increased intensity of torrential rainfall from a hurricane often produce more death and destruction than the winds of the hurricane. Fort Myers, Florida suffered such a blow from storm surge when Hurricane Ian came ashore.

New Types of Threats: “Atmospheric Rivers” have been in the news of late, especially on the West Coast of the U.S. The NOAA describes then as “relatively long, narrow regions in the atmosphere – like rivers in the sky – that transport most of the water vapor outside of the tropics. While atmospheric rivers can vary greatly in size and strength, the average atmospheric river carries an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River. Exceptionally strong atmospheric rivers can transport up to 15 times that amount. When the atmospheric rivers make landfall, they often release this water vapor in the form of significant amounts of rain or snow. “

Three people carrying belongings in flooded street with utility poles on right side and flooded homes and palm trees on the left side.
People carrying their belongings wade through water in a flooded neighborhood in the aftermath of Hurricane Ian in Fort Myers, Florida, on September 29, 2022. – Hurricane Ian left a trail of devastation across Florida with whole neighborhoods reduced to shattered ruins and millions left without power. (Photo by RICARDO ARDUENGO/AFP via Getty Images)

How are Floods Measured?

Data Required

Flood Predictions Use Several Types of Data

  • The amount of rainfall occurring on a real-time basis (i.e. how many inches of rain per hour)
  • The rate of change in river stage on a real-time basis, which can help indicate the severity and immediacy of the threat (in other words how rapidly is the river rising)
  • Knowledge about the type of storm producing the moisture, such as duration, intensity and sheer size, which can help determine possible scale and severity of the flooding. 
  • Knowledge about the characteristics of a river’s drainage basin, such as soil-moisture conditions, ground temperature, snowpack, topography, vegetation cover, and impermeable land area, which can help to predict how extensive and damaging a flood might become.
  • Mapping the Risk against how floods form; The USGS has a wealth of maps that provide detailed information in the prediction of possible flooding. Where is the greatest flood risk in the U.S.? Click here to see a map of areas at risk.

How to Survive a Flood

Prepare for Flooding: Stay Informed

Surviving a flood involves preparation and being informed of the risks.

Before a flood, be alert of your surroundings. We advise staying informed by keeping up-to-date with weather forecasts and flood warnings in your area particularly on your cell phone, and sign up for municipal emergency alerts. Create an emergency plan with your family and neighbors that includes evacuation routes, a communication strategy with family members, and a meeting place in case you get separated. As with all disasters, you may also consider preparing a waterproof “go bag” which would include essential supplies such as water and filtering device, non-perishable food, medications, first aid supplies, flashlights, batteries, important documents, and cash. Protect your home by elevating electrical appliances and utilities, installing check valves to prevent floodwater from backing up into drains, and considering flood insurance if you live in a flood-prone area.

If you find yourself in the middle of flood-like conditions, evacuate immediately if safe to do so or if advised by local authorities, and do not wait for the situation to get worse. Seek a safer area, usually uphill moving away from rivers, streams, and other bodies of water, and avoid walking or driving through flooded roads — if you must cross, make sure the water is not flowing rapidly or displaying currents. As little as six inches of fast-moving water can knock you off your feet, and two feet can sweep away a vehicle. If you are trapped, move to the highest level of your home, avoiding basements and lower floors where flooding is more severe. Stay inside and use a battery-powered radio to remain informed about the flood situation, and contact emergency services if you are in immediate danger.

How Does Climate Change Affect Floods?

The Impact

How do floods form in the first place?

Floods form from excessive water accumulation in an area, which happens as a result of various natural and human-caused processes. These these factors can act independently or in combination to produce flooding, depending on the specific circumstances of the area involved.

Climate change has become a major factor affecting flood patterns around the world in several ways:

  • Intensified Precipitation: A warmer atmosphere holds more moisture, leading to potentially heavier rainfall events. This increases the risk of rivers and streams flooding.
  • Altered Rainfall Patterns: Climate change disrupts historical rainfall patterns as is happening globally from Brazil to India. Some regions experience more frequent downpours, while others see less overall precipitation. This can lead to flooding in areas not traditionally prone to it, while some regions accustomed to seasonal floods might see less frequent occurrences. Thus we have fires in the Amazon and floods in Europe.
  • Sea Level Rise: Melting glaciers and ice sheets contribute to rising sea levels. This increases the risk of coastal flooding, as storm surges from hurricanes and cyclones have a higher base sea level to push against, causing greater inundation in coastal communities. Island nations are especially at risk from rising sea levels.
  • Faster Snowmelt: Rising temperatures can lead to earlier and faster melting of snowpack in mountains. This can cause a sudden surge of water that overwhelms rivers and streams, triggering floods.
  • Coastal Development: Continued development along the immediate coast in the U.S. has removed natural barriers such as sand dunes, natural vegetation, extensive marshes and other wetlands that once acted as a buffer to the ebb and flow of the oceans. The effect of the loss of those natural storm barriers along with the use of landfill and other development measures is now multiplied by rising sea levels and increased storm severity.

Americares on the Frontlines of Flood Response

Our History

Americares learned a great deal from the response to Hurricane Katrina in 2005. The flooding that overwhelmed New Orleans proved to be the most destructive element of the storm. The levees and other flood control measures that had been a part of New Orleans storm preparation along with the loss of natural ocean buffers along the Gulf Coast proved inadequate to counter the destructive force of Katrina. Much of recovery work after Katrina has informed our response to flood disasters since, such as the flooding of Houston from Hurricane Harvey that set a new record of 51 inches of rainfall. With each new crisis, we add new capabilities to support the response.

Our latest flood response in Libya 2023 – an extreme weather front that brought floods to Greece, Turkey and Bulgaria, has proven deadly in Libya, causing the failure of two dams and killing thousands.

Street sign that says "Humanity" and "St. Roch" is surrounded by flood water.
Katrina aftermath in New Orleans.

Our Response Involves Key Areas of Support

When water damage to a health facility destroys equipment, medicine & supplies and renders the facility inoperable when it is most needed, we now work to either reopen the damaged facility quickly or provide a temporary home. In 2016, for example, in Robert, Louisiana (an area that was not known as facing a major flood risk), two separate floods struck within months (the second bringing 4 ft, 3 in. of water) and rendered the Total Family Clinic inoperable. With the clinic facing a complete shutdown, Americares supplied a temporary structure allowing the staff to continue serving their patients.

When flood waters drive people from their homes to temporary shelters, we quickly supply hygiene kits, emergency medicine and supplies for those who had to flee quickly without their personal belongings or medications. Supplies such as mosquito bed nets, insect repellant, water purification and cleaning materials and tetanus vaccine are also important for those who return to their homes in the aftermath and face possible water and vector borne diseases and cleanup injuries. Prior to Hurricane Irma hitting Florida, we had pre-positioned medicine and supplies so we could quickly get them to our local partners immediately after the storm.

Loss of power leads to loss of medicines that require refrigeration such as insulin and vaccines. Supporting the use of solar power, water filtration systems and generators helps keep clinics open to provide critical care.

Keeping our clinic partners up and running during a flood disaster that can last for days, weeks and months underlines the importance of those relationships. It has been the key to our responses in:

In other flood disasters, relief supplies for survivors or medical teams are our focus:

Americares provides a benefit to the community under regular circumstances, but having that relationship with an organization that is an expert in disaster relief and is able to provide boots on the ground is of tremendous value. I don’t think you can put a dollar amount on that.

Heidi W. Bunyan, the chief operations officer of San Jose Clinic in Houston

Temporary Hope Town Clinic sign made on plywood with red spray paint.
Temporary Hope Town Clinic

Preparing for Flood Disasters

Knowing the Threats

Climate change and the resulting extreme weather events create specific challenges for Americares Emergency Response Team and our health care partners, and good planning provides response solutions. Building Resilience into the health system as the threats from climate change multiply becomes more and more critical. Beyond repairs, the next step is to help build Climate Resilient Health Centers. Then we work with communities to develop action plans in preparation for a flood disaster.

In El Salvador, a community facing a continuing threat of flooding has come up with a lo-tech and locally designed early warning system. This kind of innovation comes from the community with the local understanding of what can actually work for them to limit the danger from floods. We lean on local knowledge and experience to build preparedness plans that provide real protection for the community.

Get the Five Steps to Ready and be Prepared for the Next Severe Storm:

5 steps to Ready for Hurricanes - downloadable pdf

As we get ready for the next flood disaster, we know that we can’t do it without you.

Please help your neighbors near and far with a gift right now.

Our Work:
Responding to Extreme Weather and Other Disasters