History of Floods

There are few places on Earth where people need not be concerned about flooding. Any

place where rain falls is vulnerable, although rain is not the only impetus for flood.

A flood occurs when water overflows or inundates land that's normally dry. This can happen

in a multitude of ways. Most common is when rivers or streams overflow their banks.

Excessive rain, a ruptured dam or levee, rapid ice melting in the mountains, or even an

unfortunately placed beaver dam can overwhelm a river and send it spreading over the

adjacent land, called a floodplain. Coastal flooding occurs when a large storm or tsunami

causes the sea to surge inland.

Most floods take hours or even days to develop, giving residents ample time to prepare or

evacuate. Others generate quickly and with little warning. These flash floods can be

extremely dangerous, instantly turning a babbling brook into a thundering wall of water and

sweeping everything in its path downstream.

Disaster experts classify floods according to their likelihood of occurring in a given time

period. A hundredyear

flood, for example, is an extremely large, destructive event that

would theoretically be expected to happen only once every century. But this is a theoretical

number. In reality, this classification means there is a onepercent

chance that such a flood

could happen in any given year. Over recent decades, possibly due to global climate

change, hundredyear

floods have been occurring worldwide with frightening regularity.

Moving water has awesome destructive power. When a river overflows its banks or the sea

drives inland, structures poorly equipped to withstand the water's strength are no match.

Bridges, houses, trees, and cars can be picked up and carried off. The erosive force of

moving water can drag dirt from under a building's foundation, causing it to crack and

tumble.

In the United States, where flood mitigation and prediction is advanced, floods do about $6

billion worth of damage and kill about 140 people every year. A 2007 report by the

Organization for Economic Cooperation and Development found that coastal flooding alone

does some $3 trillion in damage worldwide. In China's Yellow River valley, where some of

the world's worst floods have occurred, millions of people have perished in floods during the

last century.

When floodwaters recede, affected areas are often blanketed in silt and mud. The water and

landscape can be contaminated with hazardous materials, such as sharp debris, pesticides,

fuel, and untreated sewage. Potentially dangerous mold blooms can quickly overwhelm

watersoaked

structures. Residents of flooded areas can be left without power and clean

drinking water, leading to outbreaks of deadly waterborne diseases like typhoid, hepatitis A,

and cholera.

But flooding, particularly in river floodplains, is as natural as rain and has been occurring for

millions of years. Famously fertile floodplains like the Mississippi Valley in the American

Midwest, the Nile River valley in Egypt, and the TigrisEuphrates

in the Middle East have

supported agriculture for millennia because annual flooding has left millions of tons of

nutrientrich

silt deposits behind.

Most flood destruction is attributable to humans' desire to live near picturesque coastlines

and in river valleys. Aggravating the problem is a tendency for developers to backfill and

build on wetlands that would otherwise act as natural flood buffers.

Many governments mandate that residents of floodprone

areas purchase flood insurance

and build floodresistant

structures. Massive efforts to mitigate and redirect inevitable floods

have resulted in some of the most ambitious engineering efforts ever seen, including New

Orleans's extensive levee system and massive dikes and dams in the Netherlands. And

highly advanced computer modeling now lets disaster authorities predict with amazing

accuracy where floods will occur and how severe they're likely to be.

Floods are natural phenomena. They can, however, turn into disasters causing widespread

damage, health problems and even deaths. This is especially the case where rivers have

been cut off from their natural floodplains, are confined to manmade

channels, and where

houses and industrial sites have been constructed in areas that are naturally liable to

flooding.

Floods

Floods are natural phenomena, which have helped to shape natural landscapes, habitats

and ecosystems in floodplains, wetlands and other lowlands. They are impossible to prevent

altogether, although measures may be taken to reduce their frequency and the damage they

cause. Floods can, however, turn into disasters causing widespread damage, health

problems and casualties.

Increased peak flood flow occurs where rivers have been cut off from their natural

floodplains, are confined to a manmade

channel, and where houses and industrial sites

have been constructed in areas that are naturally liable to flooding. Changes in land use in

rural and urban areas can also worsen floods or their effects.

The impacts of major floods in Europe may increase considerably in the future, since society

is becoming more vulnerable to the damage and disruption caused by floods, and because

floods may become more serious and more frequent due to climatic changes.

Major flood events in the Danube River Basin of the recent past ocurred in 2002, 2005,

2006, 2009, 2010, 2013 and 2014. The sustainable management of flood risks is one of the

key areas in which the ICPDR is active; you can learn more about this in our flood

management.

Storms, floods, heat waves, and drought are becoming more frequent and extreme as the

climate warms. In many cities, even a fraction of an inch of rainfall already leads to flooding

and sewage overflows. Flooding on major rivers is expected to become more likely, and

coastal communities will be threatened by rising sea levels. Severe and prolonged drought is

affecting water supply and quality. And deadly heat waves are posing a particular risk to the

young, the elderly, and the poor.

Cities and states need to take concrete steps to prepare local communities for these events.

NRDC's experts draw attention to the reality of climate change by tracking climate impacts

such as extreme weather and sealevel

rise. Most importantly, we work with state and local

officials to recognize, evaluate, and prepare for potential impacts. Onethird

of all U.S.

counties in the Lower 48 states will face water shortages by midcentury; floodplains will grow

by an average of 50 percent, perhaps doubling in size along the East and Gulf coasts; and

extreme rainfall will become far more likely.

The changing climate also increases health risks, the most deadly being a rise in the

frequency and severity of heat waves. NRDC's experts help communities prepare for a

hotter future, urging the adoption of strategies like street plantings and white roofs to

increase cooling

Our experts are analyzing how key state and local agencies are examining and responding

to these challenges. We scrutinize the use of public funds and urge the adoption of

costeffective,

climatesmart

water strategies, such as boosting water efficiency and building

more green infrastructure, like green roofs and street plantings, to absorb rain where it falls.

We are also pushing for reforms to the National Flood Insurance Program and making sure

federal, state, and local agencies account for future climate impacts in their decisions.

In the Midwest, NRDC is working closely with the City of Chicago, Cook County, DuPage

County, and the State of Illinois to develop strategies for dealing with the growing problem of

urban flooding. Rainfall regularly overwhelms the region's stormwater infrastructure, causing

flooding and sewer backups into basements and belowgrade

apartments. Because climate

change means more extreme rainfall, we are helping identify creative ways that green

infrastructure, targeted gray infrastructure improvements, changes in state and local policies,

and innovative financial tools can help prepare the region.