Return of the Dust Bowl?
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Earlier this year, meteorologists at Accu-Weather, a commercial meteorological firm in Pennsylvania, released an extended outlook that mentioned the possible return of “Dust-Bowl” type conditions to portions of the central United States. The Dust-Bowl era of the 1930s (especially 1934 and 1936) included some of the most severe heat and drought conditions experienced in the central United States during the last century. Many of the climatological records in Michigan for extreme maximum temperatures, including the state’s all-time high temperature of 112°F at Mio (July 13, 1936), were set in the 1930s.
The rationale for the outlook is associated with unusually warm sea surface temperatures over portions of the northwestern Atlantic Basin (The same warm waters that helped fuel a record number of tropical storms and hurricanes last summer and fall.) and relatively cool water in the eastern Pacific. These anomalous sea surface conditions were also thought to be in place during the 1930s and are thought to be associated with a westward shift of the low-level jet stream from just above the surface up to about 4,000 feet. The low-level jet stream is critical as to precipitation climatology across the Great Plains region as it acts to transport large quantities of Gulf of Mexico-origin moisture (the major “raw material” of precipitation) northwestward into the region.
Under the current scenario, the low-level jet stream would shift westward and flow more frequently over sections of arid Mexico (instead of the Gulf), reducing the amount of water transport into the United States and to less precipitation. There is another related issue referred to as an atmospheric “feedback” mechanism. When the earth’s surface is relatively well-watered (i.e. frequent precipitation), a significant amount of incoming solar energy goes into evaporating water. This can account for more than half of the total incident solar radiation. If there is less water to evaporate (i.e. low rainfall), a larger fraction of the incoming solar energy goes directly into heating the ground surface and the air above it, leading to relatively higher air temperatures. In addition, a portion of the water that falls as precipitation in the Great Plains is of local origin (The evaporation took place recently within a few hundred miles.), a phenomenon referred to as “precipitation recycling.” Therefore, prolonged drought can also reduce the amount of water available for future precipitation, which lends some scientific foundation to the old saying, “drought begets drought.”
Overall in this case, the forecasters believe that a reduction in regional precipitation over an extended period (months or years) will lead to a drier, warmer landscape. So does this mean that we will be looking at scenes from the Grapes of Wrath across sections of the central United States anytime soon? Only time will tell. Drought conditions as depicted by NOAA’s Palmer Drought Index are currently reported across large areas of the Rocky Mountain and Great Plains regions and current long lead outlooks do suggest warmer than normal temperatures across large sections of the southern United States (The NOAA long lead forecasters take the dry soil feedback mechanism into account as well.).
One thing is certain. The extreme conditions of the 1930s did not materialize overnight. Many months and even years of anomalous weather were involved, and some of the conditions were associated with poor land management practices that do not exist (or are not allowed) today. It is also worth remembering a helpful old rule-of-thumb adage that I picked up as an undergraduate meteorology student: Never forecast a new record. There is truth to this adage as climatological records represent the most extreme events observed, which means their probability of occurring is extremely small. Hopefully, that will remain true in this case as well.