Floods and Drought - Geography

Floods and Droughts

By: Adam Campigotto, Dane Macri, and Matt Morencie

What Causes Floods? • Floods are an excess of water that covers land that is normally dry. • This can be due dam or levee failures, more rain than the landscape can dispose of, torrential rains caused by storms, rapid snow melts, or a blocked river.

Factors To Predict Floods

The Two Main Floods • Flash floods occur when

• Riverine floods occur

heavy rainfall persists for only a short time period (usually only a few hours), yet can cause major damage and death due to their sudden arrival. • Flash floods can also be caused by dam bursts or overflows.

when water rises above its natural banks, often caused by snowmelts in combination with prolonged and heavy precipitation. • Riverine floods take days, weeks, or months to rise to its max and return to normal, much longer than it takes a flash flood to.

What Causes Droughts? • Droughts are caused by a lack of precipitation in an area resulting from weak or less frequent storms and other weather systems than normal. • Most major droughts last for months or years. • What is considered a drought in a rainy location may be enough precipitation for another region.

When Do They Occur? • Floods can occur any time of the year. • Floods occur primarily in the spring season due to ice and snow melting and frequent storms. • In some countries, there are monsoon seasons, a time of great rain, when floods often occur, then a dry season, when drought conditions occur.

• Droughts can occur any time of the year. • In North America, droughts occur most often between March and September, when it is often dry and hot.

Where Do Floods Often Occur? • Floods occur all over the world, except for in Antarctica. Highlands are also unlikely to be struck by flooding.

• They often occur in urban areas where water cannot drain into the soil properly. • Floods usually affect floodplains, low lying, flat areas near large bodies of water.

Major River Floods in 2002

The areas in red are where river floods have occurred this year.

Where Do Droughts Occur? • Areas that have frequent and severe droughts are shown on the map as the darkest shaded areas, and less sever droughts are the lightly shaded areas. • They usually are most severe around the 30° latitudes, where dry, cool air is falling. • Asia, many African countries (I.e. Kenya, Ethiopia, Somalia), are most often affected by droughts.

• Humid areas are prone to short term droughts, whereas arid regions are prone to long term droughts.

Have They Occurred Near Here? • There have been

• In Windsor, there have

floods in Windsor. • The Detroit River and River Canard have exceeded their natural boundaries during the 1970’s.

been many droughts, but none of great severity. • In 2001, Windsor had a drought season, affecting River Canard, crops, and other plants.

Recent Floods. • Morocco has experienced a flash flood recently, killing over 60 people. The flood has cause $1.75 million in damages. • Another flood has recently hit Costa Rica, leaving thousands homeless.

Recent Droughts. • Australia has recently been through drought conditions. The drought is occurring around Sydney. Fires have begun due to the dryness of the land. • Ethiopia is also in a drought, and is expecting over 11 million people to be without food next year due to crop failures.

Destruction by Floods • Floods can cause major structural damage to buildings, kill plants and animals, destroys habitats, and removes soil. • Floods cause many deaths and drown many plants and crops, and hundreds of millions of dollars in damage. • Many nutrients in topsoil are brought downstream or deposited in the ocean.

Hazards of Floods • There are 6 categories to

• Depth is simply how deep

tell how severe floods are in a region. • They are depth of water, duration, velocity, rate of rise, frequency, and seasonality. • Frequency is how often floods occur in an area, which depends greatly on the topography and climate. • Seasonality is the time of year floods often occur.

the water is. • Duration is how long the water lasts for. • Velocity is how quick the water is moving; the faster it moves the more damage done. • Rate of rise is how quickly the depth of the water increases. (important when giving warnings to evacuate areas)

Destruction by Droughts. • Droughts cause major damage to crops and animals, especially if they occur during the region’s growing season. • During a drought not enough water is provided to support living things. Crops can decrease 10%20% during a drought. • Droughts affect reservoirs, water supplies, water tables, and topsoil. Water levels drop, and topsoil becomes dry and less favourable to plants. • Areas that are in a drought are more likely to have wildfires than other regions.

How Often Do They Occur? • Floods can occur anytime of the year. • It is difficult to predict when floods will occur in many regions. It may be decades between floods in certain areas. • Certain regions flood several times a year (5 or more). • There are an average of 100 to 150 extreme floods annually, world-wide.

• Droughts can occur anytime of the year. • Near the equator, regions may experience 2 or more droughts per year.

Weather That Causes Floods. • Floods are caused by melting snow and ice, severe storms, hurricanes, tropical storms, monsoons, or prolonged or sudden rain fall. • El Niño is a major contributor to flooding globally.

Monsoons, Floods and Droughts • Monsoons are seasonal winds that bring heavy rains one part of the year and dry air the other. They occur in parts of Africa, Australia, Asia, and South America causing floods in the wet season, and droughts in the dry season. • During the wet season, the land is heated causing the air to rise, creating a low pressure area. Air currents coming from above a body of water rush in to replace the warm rising air. These winds from off the water carry much water causing heavy rainfall and, usually, flooding.

• During the winter, when the water is warmer than the land, a low pressure system builds over the water, and a high pressure system builds over the land. As the air currents move from the high pressure above the land to the low pressure above the water, little precipitation is brought to the land, because the air is rushing from an area above land, which will have little moisture. This causes the dry season; the time when many droughts occur.

Weather That Causes Droughts. • Droughts occur when weak or less frequent precipitation occurs than normal. • When dry air cools and falls, lowering relative humidity and the level of precipitation, conditions that can bring droughts occur. • During a drought not only is there little precipitation, but the moisture from the soil must also leave into the atmosphere through evaporation and transpiration.

Other Facts • Floods account for 40% of all deaths caused by natural disasters. • In an average year, floods account for about 200 deaths and $2 billion of damage in the U.S. alone. • In 1937 floods removed 300 million tons of topsoil in the Ohio Valley. • The world’s longest drought occurred in Arica, Chile, from October 1903 to January 1918. No rain fell for over 14 years.

THE END Thanks for your Attention!!