The drought ravaging U.S. corn crops this summer may remind some of the horrific Texas region droughts of the 1950s. Yet scientists studying those droughts found that today’s droughts in the region are more likely to be much hotter. This double whammy of drought combined with higher temperatures can turbo charge evaporation rates, which dries out soils even more and wreaks havoc with crops and livestock that can suffer immensely in the scorching heat without irrigation or other mitigation efforts.
Natural causes of drought
When, where, and how long droughts last in drought-prone regions of the world is due in part to the natural variations of ocean states that go by a bevy of different names. Some are more colorful than others (El Niño/La Niña; Atlantic Multidecadal Oscillation, Arctic Oscillation, and so forth).
The symphony that plays out each year as each ocean basin strikes a chord for the season can bring soothing rain to some parts of the world and at the same time leave other regions parched and drier than normal. For example, Julio Betancourt and others have published studies that link shifts in the Pacific Ocean turning colder at the same time the Atlantic Ocean turned warmer to severe drought in parts of Texas, Oklahoma, Colorado, Arizona, and New Mexico during the early 1950s. This ocean pattern was associated with severe and long-lasting “mega-droughts” at times in earlier centuries. Relief was finally brought by a strong Pacific Ocean El Niño phase in 1957 to 1958.
Changing character of drought in a warming world
While the various ocean states can influence the places where rain or snow may or may not fall on land, the temperature of the air and the soil in a region play a role as well regarding the severity of the drought. This is where climate change consequences kick in.
I draw upon the example of piñon (Pinus edulis) trees in the U.S. Southwest that experienced their share of rainy and dry periods over the centuries. When comparing the die-off during the 1950s drought compared to the die-off during a 2002 to 2003 drought, researchers found that the latter drought was devastating — around 90 percent of piñon trees died. They pointed to drought, bark beetle damage and higher temperatures as factors, with the latter getting most of the blame. David Breshears and co-authors called this dramatic die-off of ancient trees in the four corners region of the southwest a “global-change-type drought.”
Different definitions of drought and the historic 2012 U.S. drought
Drought can be defined in different ways:
- Meteorological Drought – Below normal precipitation over a period of time
- Agricultural Drought – Dry soils that lead to reduced crop production and plant growth
- Hydrological Drought – water in rivers, lakes, aquifers, and reservoirs fall below average long-term levels.
No matter how it is defined, these conditions often occur at the same time and we use the general term drought. We don’t say the Sahara is in a drought as we expect it to by dry. It is the change from the historical average at a particular location that can be devastating to people, plants, and animals accustomed to certain conditions each season.
Climate assessments have weighed in. The Intergovernmental Panel on Climate Change (IPPC) stated in the 2007 assessment report: “Globally, the area affected by drought has likely increased since the 1970s.” While the recent report of 2012 on extreme events known as the SREX report assessed future risk and stated: “There is medium confidence that droughts will intensify in the 21st century in some seasons and areas, due to reduced precipitation and/or increased evapotranspiration.”
As of July, the percent area of the continental United States afflicted by drought was the largest to date in the 12 years of record keeping. By June the U.S. drought was already the largest moderate to extreme drought since the 1950s, according to the Palmer Drought Severity Index.
Let’s hope natural variability can give a temporary reprieve and take the sting out of these hotter droughts in 2012.
Stay tuned as our series on the 2012 Drought in America next turns to the energy and drought collision in a post by Erika Spanger-Siegfried, followed by more posts touching on topics such as the ability of agricultural systems to adapt to extreme droughts.
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