The decade that became known as the “Dirty Thirties” was literally quite what its name implied-dirty! During the period of 1930-1940, located in the heart of the Great Plains of the United States, was a series of massive dust storms and long-term drought. Another well-earned nickname this region was known for was the Dust Bowl. The Great Depression occurred at this time as well and added to the suffering placed upon the many poor farmers of the Southwest region. What could have caused one of the worst and longest droughts in recent U. S. history?
Unfortunately, decades of human influence from bad farming practices, loss of soil moisture, and depletion of vegetation helped create wind-blown erosion that shaped the massive dust storms and severe droughts. Other natural causes were unusual weather patterns: warmer Atlantic and colder Pacific sea-surface temperatures, feedback mechanisms from dry air, and a strong jet stream confined to the north of a continental high pressure system that left little chance for rainfall. Many of the residents of the Great Plains during the Dust Bowl were poor farmers reliant on agriculture to sustain their income and family’s well being.
An usually wet season before the 1930s brought many farmers to the central U. S. to cultivate and settle the area. Unfortunately, the climate and soil conditions changed drastically after the start of the 1930s. Once it began, the severe drought, dry soil, and dust storms made planting crops almost impossible. Farmers with livelihood’s lost and future looking bleak packed up their families to look for better prospects elsewhere. Hundreds of thousands of these individuals started a great migration to places farther west like California. They became known as “Oakies” because many traveled from Oklahoma in their familiar dust-covered trucks.
The novel, “The Grapes of Wrath”, describes the story of a Dust Bowl sharecropping family traveling to California after experiencing hardship from drought coupled with the effects of the Great Depression. Furthermore, its fictional account was in fact very similar to how the real-life farmers and their families were affected. The migration routes and the region at the heart of the Dust Bowl can be seen in Figure 1. However, one positive outcome was that Great Plains farmers, government officials, and scientists learned to develop better farming techniques and practice soil conservation or a sustainable future. Undoubtedly, the decade of the 1930s was one of the greatest disasters in American history attributable to meteorological causes. It became the standard for describing drought. Four specific drought events took place during 1930–1931, 1934, 1936, and 1939–1940. The drought periods that helped produce the creation of the widespread dust storms were characterized by several factors. A mild, moist winter with a shift to dry conditions in mid-April around the central U. S. preceded the start to the beginning of the Dust Bowl.
In addition, another preceding event was rain deficiency in the fall of 1929 on the California coast. Severe dust storms and drought was felt in Oregon, California, Washington even before the Great Plains did. Winds carried the dry air from the interior to the Southwest (Tannehill 1947). Heavy rains that fell in the Great Plains before the 1930s was a short-lived, deceptive event while a national decade long rain deficit occurred in surrounding regions. During 1934, over 80% of the U. S. experienced moderate drought. (Rosenberg, 1978). For example, in Goodwell Oklahoma, they had a nine inch rainfall deficit in 1932 and 1933.
Over the 11 year span from 1930-1940, a large part of the region saw 15% to 25% less precipitation than normal (Hurt 1981, 29). Referring to Figure 2, we can see that specifically the Missouri basin region experienced drought at close to 95% around the time of 1935 to 1940. Figure 2: Percentage of Area in Missouri Basin that experienced severe Drought. Jan. 1895-Mar. 2004. Source:http://www. drought. unl. edu/whatis/palmer/missouri. gif Figure 1: This drought Index details the areas across the United States that were the hardest hit in the 1930s during the Dust Bowl and migration routes.
Source: http://www. spartacus. schoolnet. co. uk/USAdustM. JPG Heat waves were extreme during that time and were caused by the dry land that had no moisture to cool down the high heat. Record setting high temperatures occurred in 1934 (Rauber et al. 2002). Tannehill explains: “… the heat and dryness of the air are caused not only by absence of cloudiness and failure of rain but also to a large extent by air from other than the normal sources” (Tannehill 1947). To add to the problem, plagues of insects that excelled in the dry environment ate the little crops that did grow (Tannehill 1947). It was so heavy and thick. It wasn’t like sand. It was just real heavy, like face powder. Only it was real dark, almost black” (Glover n. d. WGBH American Experience. Surviving the Dust Bowl). Here Glover, a witness of the Dust Bowl, describes what must have been a terrifying event.
As we can see in Image 1, her description is quite similar to the photo that shows a massive, dark dust cloud moving across Colorado. Image 1: A cloud of thick dust, hundreds of feet high moves over farms in Colorado. Source:http://www. weru. ksu. edu/new_weru/multimedia/dustbowl/big/usda18. pg. The atmospheric conditions that lead up to the Dust Bowl of the 1930s were factors that prolonged the life of the severe droughts, strengthened the heat waves, and amassed the massive, unrelenting dust clouds. The Great Plains is known as a transition zone between the humid east and the arid southwest where dust can be blown with gale force, 50 + mph winds from the interior to the Southwest. This dry zone, deplete of moisture in the air and subsoil, helped the series of droughts to “feed upon itself” through feedback mechanisms ( Rauber et al. 2002).
As a result of the lack of water vapor, there was a reduction of evaporation levels so the cooling effect was reduced. Once the opportunity for cooling is reduced, the heat wave is strengthened by radiational heating (energy as electromagnetic waves radiated by the high temperature of the surrounding area) that is increased from the lack of clouds to reflect the sun’s rays (Rauber et al. 2002). Furthermore, a strong high pressure system above (700mb) the Central Plains with a jetstream farther north than its normal position stays stationary as it continues to “feed upon itself”.
The system is usually located more south in normal seasons with a more weakened low-level system that brings summer thunderstorms and precipitation. Rainfall amounts, as earlier mentioned, before the beginning of the droughts were abnormal because of the irregular sea surface temperatures of the Atlantic and Pacific in addition to a departure from the normal weather pattern. This can be explained by the unique connection between the atmosphere and land surface conditions that can help prolong the drought conditions and lower precipitation levels (Schubert et al. 2004).
Another atmospheric condition that created the “Dirty Thirties” was the strong heating near surface air that caused clear skies, along with humid conditions, that left little chance for precipitation to form in drought regions (Rauber et al. 2002). During the dust bowl, the atmospheric conditions helped reinforce the drought circulation patterns allowing for fine soil to be eroded and carried by the strong, continental winds. Figure 3 shows the Palmer Drought Index for July 1934 and its long-term hydrological conditions. In the Great Plains it was below -4, which equals an extreme drought.
This index measures moisture deficiency that is standardized to local climate conditions. It can follow drought periods because it is cumulative to a time periods precipitation amount and temperature’s prior value to the previous indexes. It is a “relative measure” compared to surrounding regions (Rauber et al. 2002). Figure 3: The PDSI for July 1934 of the hydrological conditions of the U. S. Source: http://weather. about. com/od/imagegallery/ig/Global-Warming-Images-Graphs. –5K/Palmer-Index-US-Dust-Bowl-Map. htm Furthermore, a third high pressure ridge developed aloft over the interior of the U.
S with a jetstream that moved further north into Canada. It became confined to the cloudless region north of the continental high pressure with the continued warming of the hot, dry region of dense air that expanded and “clinged” near the surface, reinforced the feedback mechanisms, and blocked the influx of low-level rain from the Gulf (Rauber et al. 2002). Although the end of the Dust Bowl was not clearly identifiable, the return of the rains in a series of 1940 downpours from low pressure systems are considered an indication.
The unusual currents of the flow of the jet stream and SSTs returned to normal (Hurt, 1978). In conclusion, 1941 was the wettest year in the period from 1886 to 1944, which helped mark the end of the droughts and Dust Bowl (Tannehill, 1947). Clearly, the Dust Bowl period was aggravated by human action-it proves we can affect weather through our interaction with nature. Farmers and the government alike seemed to realize this after the end of the “Dirty Thirties”. Soil conservation and changes in farming techniques appeared after 1930s (Rosenberg 1978, 125).
Great Plains farmers implemented terrace, contour, and strip farming. These methods prevented soil erosion while also capturing more moisture that prevented extreme droughts and dust storms from reoccurring. Newly formed laws for soil conservation urged farming districts to unite to combat soil erosion and the misuse of land (Hurt 1981, 74). The severe drought periods caused massive resettlement patterns in the Central Plains and produced lasting effects on the water tables of that region. In addition, the widespread use of vital irrigation in growing crops in agricultural areas was seen after the Dust Bowl ended.
Droughts kill more people every year than any other weather phenomena (Rauber et al. 2002). That is why studying the Dust Bowl and its causes is important to understanding how to prevent similar severe weather events. The dust storms that caused such extreme hardships on the people of the Great Plains did create positive discussions on how to respect our environment and learn to practice sustainable, responsible land use. It also showed the amazing resilience of the American plains farmer who not only survived the Great Depression but the “Black Blizzards” that turned day into night as well.
We must always be cautious for our future as the interconnection between human interaction (greenhouse gases, water depletion, etc. ) and our susceptible atmosphere can perhaps lead to similar, even longer, droughts. Currently, global warming accelerates the drying of the Southwest region of the U. S, in addition with widespread lowering of the water table by irrigation reliant agricultural regions. (Rauber et al. 2002). It makes one wonder if in our lifetime we could we see a “Dust Bowl of the 21st century”?