Crane-Station wrote up a very good post on this topic yesterday here at FDL. I didn’t want to step on their toes, so waited to post mine until today. Hopefully this adds to the discussion and doesn’t duplicate too much.
The National Climate Data Center, in its summary of drought conditions as of the end of June 2012, reported that 55% of the contiguous U.S. was experiencing moderate to extreme drought, as the graphic below shows. This is the largest percentage since December 1956 when 58% of the U.S. experienced similar conditions. The Palmer Drought Index, whose data base goes back 112 years, is relied upon for drought comparisons before 2000.
Figure 1. Drought conditions across the United States as of early July 2012 from the Drought Monitor.
In my last post on drought, I stated, “There’s no widespread crisis to speak of yet, but inhabitants as well as policymakers should monitor conditions as the year progresses.” Well, the NCDC established the case for a widespread crisis with their latest summary, which was not issued until after my post. Crops and livestock are now being negatively affected. The following two charts show corn and soybean prices. The recent peaks are due to worsening conditions across the breadbasket and the USDA’s recent crop downgrade.
Figure 2. Corn (top) and soy (bottom) prices and volume charts for the past 12 months.
1988 was also a very bad year for corn in the U.S. Here is a chart from the USDA comparing 1988 and 2012 corn ratings:
Figure 3. Comparison of corn ratings (good + excellent) as determined by the USDA as of early July 2012.
You can see that conditions in 1988 worsened earlier in the year (solid blue line @30% ~3 weeks before the solid yellow line). It remains to be seen how bad conditions eventually get in 202.
So conditions are the worst since Dec. 1956. How else do today’s conditions compare to earlier droughts? The following graphic from USA Today helps put them in context:
Figure 4. Comparison of extensive drought in U.S. history.
The percentage of the country in moderate to severe drought in June 2012 is the sixth highest since 1900. The 1930s are well known as Dust Bowl years. Conditions aren’t expected to get that bad, even if drought were to dominate the area for the next few years, primarily because of changes in farming practices. Topsoil was easily scoured from the earth in the 1930s and was moved around by winds, sometimes for dozens or hundreds of miles, hence the name ‘Dust Bowl’. The droughts of the mid-1950s were also quite extensive. The U.S. is fortunate that the return period of these conditions was ~55 years.
I’ve also written in my drought posts that the current drought, extensive and intense as it is, is not without historical precedent and that a clear climate change linkage is not available at this time. With generally warmer temperatures and more variable precipitation patterns, one might conclude that drought would be more likely to occur in recent years than in the 1900s. As the USA Today chart shows, that clearly hasn’t happened. The conditions in 2012 are more closely related to the double-dip La Niña that just ended:
Figure 5. Time series of temperature anomalies in the NINO3.4 region. Positive values for 5 consecutive 3-month periods correspond to El Niño events while similar periods with negative values correspond to La Niña events.
This drought is very serious and everybody should treat it as such Part of that statement is acknowledging the lack of a clear anthropogenic climate change signal at this point in time. Conditions aren’t expected to significantly improve in the next couple of weeks. The extent and intensity of drought can expand and worsen within that time. We can also expect higher prices for food starting next year and into 2014 – additional economic headwinds that the U.S. can ill-afford at this time.