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Droughts and Heat Waves

Page history last edited by Ian MacLean 12 years, 9 months ago

Droughts and Heat Waves 




Authors: Joe Weiner, Ian MacLean, Jonathan Philipp

Contact: Weiner4@illinois.edu, maclean1@illinois.edu, philipp3@uiuc.edu



Opening Statement




      Worldwide draught cause more deaths than any other weather disaster. The annual average of costs and losses from floods and hurricanes in the United States combined is less than the average annual costs and losses from drought in the United States. On average, drought causes $6-8 billion in losses and other expenses in the United States alone. Drought has caused mass migrations that have shaped the demographics of the United States. During the 1930s over 2.5 million people fled the Great Plains for the west coast because the severity of the drought (www.drought.unl.edu). Drought not only affects humans but thousands of animals also die during drought as shown in the picture to the left. Drought is very relative to location because every place on the earth has a slightly different ecosystem and therefore drought affects each place differently.


Drought in Ethiopia results in animal deaths

Source: www.Guardian.co.uk





    There are three different types of droughts. The first type is meteorological drought is when the precipitation is below average for an extended period of time. The second type is Hydrological drought is an unusual lack of groundwater in an area. The third type of drought is Agricultural drought is when there is a lack of moisture in the soil making crops unable to grow normally.  Drought in the central and eastern United States is based upon spring and summer weather while drought in the west is based on weather during the winter. The main cause of drought is the lack of precipitation.


Three types of drought

Source: www.eea.europa.eu

               One of the leading causes of weather related deaths are heat waves, which often accompany drought. By definition a heat wave is unusually high temperatures over a period of time. On average 237 people die each year from heat related issues because intense heat aggravates many illnesses and causes sunburn, heat cramps, heat exhaustion, and heat strokes (http://www.nws.noaa.gov). One of the worst heat waves in United States history took place in July 1995 where over 1,000 people died during the heat wave. Compared to other heat waves it was relatively short lasting only four days, July 12-15. The reason it was so deadly was because Chicago was near the core of the heat wave, which when added together with urban heat island effect resulted in extremely high temperatures. The diagram to the right shows the amount of deaths during the heat wave. During the 1930s the United States Great Plains suffered through heat waves that led to the droughts in the Dust Bowl that were previously discussed. Some people believe that with global warming we will see an increase in the amount of heat waves, but this is yet to be proven true. Some models actually say the opposite and claim we will have more precipitation then usual with global warming which will reduce the amount of heat waves. The only thing that has been proven so far is that nighttime temperatures in urban areas have been increasing. Either way heat waves or droughts still do occur and affect millions of people every year.







Deaths in Chicago heat wave of 1995

Source: www.eetd.ibl.gov/insurance-research/tech.html







           Droughts and heat waves are some of the most destructive and devastating meteorological phenomena on the planet and yet they are some of the hardest to identify. Throughout history, droughts and heat waves have been a significant area of concern for scientists because they are the number one cause of fatalities worldwide and yet are still quite ambiguous to identify.  A drought is a significant deficit in moisture due to lower than normal rainfall amounts and a heat wave is an extended period of above average temperatures (1). However, it is hard to say exactly when a drought begins or ends because they produce complex effects that accumulate slowly and interact with the resource demands of humans for fresh water.

        Drought can be measured by several different indices but there is no universal amount of rainfall that signifies a drought. A drought is evaluated by measuring the amount of precipitation, temperature, and soil moisture data, for the present and past months. Using this data, meteorologists can calculate a Palmer Drought Severity Index, which presents all of the data in an easy to understand index. Values of the PDSI range from -6.0 (extreme drought) to +6.0 (extreme wet conditions).  Using this index along with several others, the National Drought Monitor releases weekly maps that portray the current drought conditions across the country.



U.S. Drought Monitor for October 28, 2008





       As seen in the map at the right, droughts vary in size and severity depending on the conditions in the region. In the figure shown, there is currently a severe drought in the southeast United States that covers a huge expanse. However, there are also several smaller regions where drought is influencing a few counties. Even though a drought may not be too severe, its societal impacts are still undeniable; on average, droughts cost the U.S. economy 6-8 billion dollars in lost crops and other agricultural resources (2). While droughts are not as easily visible as tornados or hurricanes, they cause a significant amount of damage to our crops and our thus, our economy.  Another reason droughts can be so costly is the length of their lifetime. Depending on the severity, droughts can last years and be devastating to our economy such as the Dust Bowl of the 20’s and 30’s. Others can be as short as a few weeks to a month.  


Major Past droughts




         From year to year there is always at least one region of North America experiencing drought conditions. However, during certain time periods severe droughts arise that last several years and cause fundamental changes to the economy of the United States.  For example, the drought of 1950 in Texas changed the methods for irrigation. Due to the fact that ground water levels dropped 50-100 feet, farmers had to dig wells that fed sprinkler systems in order to keep their crops irrigated. The figure at that right shows the results of these irrigation methods as seen by satellite.

        It is often found that heat waves are found with droughts, however neither directly causes the other. Heat waves on their own are destructive in that they claim around 237 lives a year but when combined with a drought they can be extremely deadly (3).  One way that meteorologists attempt to warn people about heat waves is through the Heat Index. This allows meteorologists to calculate what it “feels like” outside using the temperature, relative humidity, and location.  Depending on the heat index the National Weather Service can issue a heat advisory (3). 

      Briefly, heat waves are formed by the absence of a polar air mass; heating of the surface due to the lack of cloud cover, dry ground, and the vertical mixing of air. Because dry ground is an ingredient for heat waves, there is a large positive feedback between heat waves and droughts. In other words, the presence of a drought intensifies a heat wave and a heat wave intensifies a drought. Therefore, the two often come in a deadly combination.



(1)- www.drought.gov

(2)- www.drought.unl.edu/risk/us/compare.htm





Effects of drought on 1950's Irrigation




NOAA's National Weather Service 
Heat Index






          Although droughts and heat waves have similar characteristics and are often associated with one another, the truth remains that they are quite distinct in both their causes and formation.  At times they may occur simultaneously, one triggered or sustained by the other, but it is not uncommon for one to be present independently of the other due to separate meteorological triggers.  Of course, tangible triggers are difficult to determine in these sorts of weather phenomena thanks to their relative effects depending on the “normal” climate of a given location.  However, once formed the effects of droughts and heat waves can be extremely dangerous. 


Heat Wave Aerial View

          Droughts are some of the most difficult weather phenomena to forecast. The existence of a drought is associated with “large-scale upper-air waves, the jetstream, and subtropical high-pressure systems,” (1).  Specifically, the jetstream is typically located above the affected area, and high-pressure systems exist in the North Atlantic and North Pacific oceans.  Ocean surface temperatures have also been found to potentially predict the occurrence of a drought, but it is still relatively uncertain as to how exactly.  The two high-pressure systems in the oceans are joined by another that will form around the region that the drought will develop.  This will result in a number of things.  First, any moisture from above or below will be directed around the system keeping it dry, and the clear skies sustained by the high pressure will keep the region warm.  These conditions are prolonged due to the dry ground, which prevents evaporation allowing the ground to absorb more of the energy from the sun.  The severity of the drought can be measured by the Palmer Drought Severity Index.  This index is “a measure of moisture deficiency standardized to local climate conditions,” (1) and can normally range from -4 to +4 (2).  Until some form of precipitation finds a way to permeate this system, it has the potential to dramatically decrease the amount of moisture available in the area.  In addition, the warm conditions may escalate, creating the increased probability of a heat wave. 


US Drought Moniter for Thursday August 24, 2006

            The affects of a heat wave can be particularly devastating as the temperatures in a given region rise to dangerous levels.  Again, this is completely relative to the normal conditions of the region.  In general, there are four factors associated with the development of a heat wave, although “all four need not be present simultaneously,” (1).  The first involves the location of the jetstream.  It should be above the affected area disallowing polar air masses to reach the region.  Second, a high-pressure system may exist generally to the east permitting the surface to be heated in the absence of moisture.  A third related factor is a dry ground, which facilitates the heating of the surface.  The fourth and final factor is the amount of vertical mixing of the air.  Specifically, weak vertical mixing produces strong stability and the continuance of humidity near the surface. 


Rising Temperatures


(1) - Severe and Hazardous Weather: An Introduction to High Impact Meteorology (Bob Rauber, John Walsh, Donna Charlevoix)

(2) - http://www.drought.noaa.gov/palmer.html




            Deaths associated with drought are often attributed to food and water shortages rather than from people being directly exposed to the elements and losing their lives.  Droughts do have very high monetary cost though, and according to the chart on the right, from the National Drought Mitigation Center droughts on average cost more than floods and hurricanes in the United States each year (http://drought.unl.edu/risk /us/compare.htm) . In other countries though droughts cause can cause hundreds and thousands of deaths. In poor countries that rely on local agriculture as their main food source a drought can leave the country without food, which leads to starvation and death. Fortunately the United States is a large country and our agriculture industry is expansive and advanced, so unless a drought hits the entire country, which is not common, our food supply will be marginally impacted. Smaller countries are not as fortunate and drought can shut down all agriculture leaving the country vulnerable. Poorer countries often rely on help from other countries, the United Nations, and other international originations to step in and help.

            The worse drought in United States history was from 1930 until 1936, which hit the Great Plains. Combined with the Stock Market crash of 1929 and horrible economic conditions the drought was the worst weather disaster in United States history. Part of the reason the drought was so awful was because of bad farming techniques used leading up to the drought. If better techniques were used it would not have stopped the drought but defiantly could have reduced the damage. The drought became known as the “dust bowl” because it left much of the land covered in dust and not usable for farming. The picture to the right shows what was once a farm in South Dakota that was turned into a dust pile. Over half a million Americans were left homeless because of the drought, while over 2.5 million people fled the Great Plains (http://www.usd.edu/anth/epa/dust.html). This resulted in a huge migration of Americans out of the central plains and into northern cities and California. Many record high temperatures were set during the 1930s drought still remain as record highs today.

            In a normal year about 237 people die directly from heat waves in American alone! Some of the more recent deadly heat waves in United States history were in 1980 and 1995 where about 1,250 and 1,000 people died respectively (http://www.co.pasqu otank.nc.us/departments/911/webpage/heatwaves.htm). Hundreds more people are believed to die ever year from heat related issues such as diseases that were caused by the heat. Some of these heat related diseases are sunburn, heat cramps, heat exhaustion, and heat strokes. Sunburn is a redness that develops on ones skin from lots of exposure to the sun. Heat cramps are painful spasms in the muscles. Heat exhaustion often results in cold skin, sweating, possible vomiting and fainting. Heat strokes result in extremely high body temperature, above 106 ° F, this is the most deadly result of heat. 

            As an example of a recent deadly heat wave, in 1995 the United States Midwest suffered one of its worse heat waves ever on July 12-15. The death toll estimates range from 500 to 1,000 depending what is considered a heat related death! Chicago was located in the core of the heat wave and therefore suffered the worse temperatures and most deaths. (Chicago is also located along Lake Michigan so it has the nighttime urban heat island effect.)  This helped keep the temperatures in the city high even at night. During the heat wave some cities recorded 80° F dewpoint temperature. This produced heat indices that climbed to 120° F (Charlevoix). These conditions combined led to one of the worse heat waves in United States history.








Costs and Losses in the United States












What was once a farm in Oklahoma was turned into a dust pile.



Case Study

   While droughts are by no means the most glorified weather phenomenon, they are by far the most costly and even the most deadly. Droughts are the number one weather related cause of death in the world even though they are rarely publicized as much as other weather phenomena. One such occasion where a drought has left its mark on society was the Dust Bowl of the 1930’s. During this time a drought covered nearly the entire Great Plains for nearly an entire decade. More interesting than the weather behind the drought was the societal impact of it. As it is well understood, the 1930’s were already a period of economic volatility following Black Tuesday October 29, 1929 and the crash of the stock market. Having the destructive forces of drought wreck havoc across the Great Plains only worsened the situation and lead a massive decline in the U.S. economy.

            The Great Plains was primed and vulnerable for a drought because of the poor land management tactics of the 1920’s and before. In fact, the land settlement techniques of even 100 years earlier were partly to blame for the vulnerability of the region. This is because huge areas of land were given away to farmers who knew very little about the climate and fertility of the soil. Also, the first flock of settlers came during a wet cycle and they thought that was the normal climate for the region (1).  As a result, they just tried to grow more and more sucking the vital nutrients out the soil; this lead to soil erosion and massive dust storms capable of traveling across the entire country. As crop prices fell, farmers were forced to grow more and more crops to make enough money. Farming submarginal lands often had negative results, such as soil erosion and nutrient leaching. By using these areas, farmers were increasing the likelihood of crop failures, which increased their vulnerability to drought. Overall, reductions in soil conservation measures and the use of poorer lands made the Great Plains more vulnerable to wind erosion, soil moisture depletion, depleted soil nutrients, and drought. (1)






Dust Storm created from intense drought

As a result of this vulnerability, the Great Plains was struck with the most severe drought in recorded history. While the Dust Bowl is referred to as one long drought, it is actually 4 distinct drought events: 1930–31, 1934, 1936, and 1939–40 that ran together in close succession (2). As seen in the figure, almost all of the Great Plains was ravaged during this time period.  In terms of cost, the Dust Bowl was the second most costly drought in history behind the drought of 1988-89. However, it is difficult to calculate the exact costs because of the other events occurring simultaneously such as the Great Depression. It is estimated that over 2.5 million people migrated from the Great Plains to other areas of the country to escape the wrath of the drought. This led to extensive settlement of the west coast that we see today. Altogether, the most important effect of the Dust Bowl was the devastation that it caused the U.S. economy. In a period of intense economic turmoil, a very low supply of crops such as wheat only worsened the situation. People could not afford to buy the little food that was available and thousands of farmers went homeless because of their low crop yields.

            Overall, the poor land management and farming techniques of previous decades left the Great Plains vulnerable to one of the worst droughts in U.S. history. With dry soil and heavy soil erosion, the diminished rainfall for several years caused extreme drought that led to dust storms, as seen in the figure, that left the Great Plains unviable for farmers. According to most historians and meteorologists, the drought of the 30’s and the “Dust Bowl” was the worst weather related disaster in U.S. history.










(2)- http://www.ncdc.noaa.gov/paleo/drought/drght_temporal.html

PDSI Map for 1934-1939






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