Droughts and Floods

Extreme Weather

When it comes to the issue of climate change, many people instantly think about global warming, the recent and average raise in temperature of the Earth’s surface. The media discusses melting ice caps or rising temperatures and debates over whether or not it’s humanity’s fault. While global warming is an important worry that should be dealt with, it is also important to realize that climate change comprises much more than just rising global temperatures. According to the ENSAA, climate change is a long-term change in weather patterns, either in average weather conditions or in the distribution of extreme weather events, in areas like temperature, wind patterns, or rainfall (ENSAA). As a result, even weather “extremes” – that is, weather events varying significantly from average patterns (BBC) – and “normal” weather – temperatures and the number natural events that are a part of an average range –  change periodically as climate changes.

Take rainfall for example. As can be seen in the Img. 1, there has been an overall increase in annual precipitation in the US. The Environmental Protection Agency (EPA) has recorded a general increase of 5.0% precipitation in the United States since 1901 (Note: While there has been an overall increase, some areas like Hawaii and the Southwest has actually seen decreases in precipitation) (EPA). That means that if the amount of rain that is considered “normal” today happened to fall in 1901, it would be considered a severe or even extreme weather event. The same idea holds true for droughts and floods (See Img. 2). The range of extreme droughts and floods is part of a constant fluctuation, and thus should be viewed with an educated eye. Just because levels are higher than the past does not mean that they classify as extreme. At the same time, however, it is important to pay attention to the changing ranges of what “normal” weather is. Normal weather and safe or livable weather are not always the same. 

chart of unusually high precip in lower 48 states from 1895 to 2012

Img. 1

number of natural disasters reported from 1900 - 2012


Img. 2 The number of droughts and floods in the 21st century have more than doubled those in the previous century, showing how the range of what is considered “normal” weather events has shifted. It is important to be critical about these changes and be aware of what is causing them and how they can be prevented.

Extreme Drought

Stop and think: What thoughts come to mind when someone says “drought”?

Perhaps ideas such as “dry,” “desert,” or “hot” were some of the first images or feelings in your head. Maybe even “dead,” with dried-out corn, or “fire” with the forest wildfires in California. One adjective that is not as common and yet is very pertinent is “destructive.”

A droughts, very simply defined, is an extended lack of rainfall. The World Meteorological Organization (WMO) warns how it is easy to miss oncoming signs of drought because of the constant fluctuations of rain between seasons and in overall climate. (WMO) It is also easy for drought to be amplified by lack of preparation and overuse of water resources.  But the effects of drought are able to last long after the drought itself is done because of the damaging nature to crops, soil, etc, especially in cases of severe, extreme, or exceptional drought.

Drought in the United States

wilted corn crop

(Photo from USA Today showing Yutan, Nebraska)

Since the beginning of the 20th century, the US has set up programs to observe and analyze patterns of rainfall and drought. The National Drought Mitigation center and the National Oceanic and Atmospheric Administration jointly publish weekly updates on the US’s drought situation based on “measurements of climatic, hydrologic, and soil conditions” with commentary from climatologists at the U.S. Drought Monitor. These statistics are composed of data from more than 350 sources and are analyzed by 11 rotating climatologists who provide the explanation of the week. ( U.S. Drought Monitor)

In order to have a constant measuring tool when defining drought, climatologists use the following categories to classify levels of drought:

Abnormally Dry (D0) 

Going into drought

  • Short-term dryness slowing planting and growth of crops or pastures
  • Above average fire risk

Coming out of drought

  • some lingering water deficits
  • Pastures or crops not fully recovered.

Moderate Drought (D1)

  • Some damage to crops and pastures
  • High fire risk
  • Streams, reservoirs, or wells low: some water shortages developing or imminent and voluntary water use restrictions requested.

Severe Drought (D2)

  • Crop or pasture losses likely
  • Very high fire risk
  • Water shortages common: water restrictions imposed

Extreme Drought (D3)

  • Major crop/pasture losses
  • Extreme fire danger
  • Widespread water shortages or restrictions

Exceptional Drought (D4)

  • Exceptional and widespread crop/pasture losses
  • Exceptional fire risk
  • Shortages of water in reservoirs, streams, and wells, creating water emergencies.


Below (Img. 3) is a chart complied from the US Drought Monitor’s website that shows the presence of drought in the contiguous US (ie, not including Alaska and Hawaii) since Jan 2000 using the D0 – D4 categories. The normal fluctuations of water seasons and dry seasons can be seen, as drought levels in January are typically lower than those in September. The presence of extreme and exceptional drought in the US has been increasing over time in common dry seasons, and reached all-time highs in summer 2011 and fall 2012. While the cause of the increase in drought can be a variety of factors – less precipitation, changing wind patterns moving rain clouds to different areas, continued effects of previous droughts, etc – the effects include the destruction of crops and pasture lands, severe water shortages, and higher risk of fire (that can further destroy crops and even affect towns). All of these have severe consequences to both the people living in the region experiencing drought and those beyond, who have to use their own resources to make up for those lost.

drought in the 48 lower states 2000 - 2014

Img. 3 Data from: U.S. Drought Monitor

Drought Globally

Most students learn about the severe desertification in the Saharan Desert that has been going on for centuries in middle school. The process of desertification provides a great example of how changing patterns of rainfall and extreme drought can, over time, force humans to change traditional ways of life and even cause migrations to new areas. Unfortunately, these migrations result in more people localized in livable areas, causing strains on established ecosystems and town systems.

The WMO also cites Asia as the area that suffers the most from natural disasters thanks to extreme weather and climate change. Because Asia hosts 60% of the world’s population, the extent of property damage and loss of life is even greater when weather is further aggravated by fast industrialization. As a result, Asian countries continue experiencing record breaking temperatures and natural disasters. (WMO)

Extreme Floods

Like droughts, the growth of number and magnitude of floods is directly connected to rainfall patterns, which effects the volume of water in lakes, rivers, canals, the ocean, and even sewers. “A flood is a situation in which water temporarily covers land where it normally doesn’t.” (FloodSite) According to the WMO, floods can appear in a variety of forms, ranging from small flash floods to large coastal or urban floods. Some main triggers include:

  • Severe thunderstorms
  • Tornados
  • Tropical cyclones
  • Monsoons
  • Melting ice/snow
  • Dam breaks

view overhead of flooding of homes

Floods directly impact the lives of humans, bringing damage and destruction wherever they go. According to the International Federation of Red Cross, floods are the greatest cause of homelessness and affected about as many people as droughts do. (WMO)

Although more data is needed to confirm exactly how climate change and rising temperatures have affected the increase in floods, the European Environmental Agency does remark that the trend of rising temperatures will in fact intensify the water cycle by causing greater evaporation and thus a higher volume of rainfall (EEA). Water can only be absorbed into the ground so fast, which means that when more water falls, the likelihood of floods increases.

The observed increase in damage costs from extreme weather events is mainly due to land use change, increases in population, economic wealth and human activities in hazard-prone areas and to better reporting.  To confirm the exact role played by climate change in flooding trends in past decades, it would be necessary to have more reliable, long-time series data for rivers with a natural flow regime(EEA).


rushing flood waters

foundation disrupted home from flood

Pictures from Izismile showing a flood that hit Poland in Spring 2010.

There are multiple aggravators that cause floods to be more intense, more frequent, and to have a greater affect on humans.

  • Where humans choose to live
  • Living in flood plains (natural areas that rivers expand into during rainfall) – homes and infrastructure is more likely to be affected by floods every time it rains
  • Living in a city -  impermeable surfaces like concrete sidewalks or asphalt roads keep water from being absorbed into the ground and force water to be above the surface until storm drains clear out or until it reaches the limits of the city
  • Human population – with growing populations, more people are affected by floods every time


The EEA offers some ways that floods can be controlled and some of the causes mitigated through new infrastructure. For example, by giving rivers the appropriate amount of space to flood by either lowering flood plains or allowing man-made land along river banks to be re-submerged, floods would be less catastrophic to houses and buildings along the bank. Also, by expanding green infrastructure - a network of natural and semi-natural areas designed and managed to deliver a range of ecosystem services – excess water can be redirected to areas where is can be easily absorbed, thus reducing the water level in towns and cities. (EEA)


The greatest thing that everyone can easily do to help prevent droughts and floods is to be informed. Awareness about what causes or aggravates these natural events is the starting point of understanding what we can do to control or prevent the loss of property or even loss of life that comes from natural disasters. And, by knowing that climate change is one of the greatest influences to the current state of these events, it is also important to use your knowledge of how climate change is happening to make informed decisions and potentially change your own habits.

Jackie Pedroso

Last Updated: October 10, 2016