It is no surprise that US farmers had trouble with their corn and soybean crops this year – from the slowest planting on record to one of the latest-ever harvests – as above-average precipitation has been a staple in the Midwest for an unheard-of period of time.
October likely marked the 15th straight month in which precipitation was greater than the long-term average in the Midwest, where the majority of US corn and soybeans are grown. Plentiful rainfall is generally good for yields, but it is not ideal during planting or harvest, as waterlogged soils cannot support heavy equipment.
For these purposes, the Midwest is defined by the Midwestern Regional Climate Center as the area bound by Minnesota to the northwest, Missouri to the southwest, Kentucky to the southeast and Michigan to the northeast.
The Midwest has not observed a drier-than-normal month since July 2018, and the 15-month streak of abundant precipitation is incredibly unusual. The next-longest runs in records since 1895 were the eight months beginning December 2007 and the eight months beginning June 1951.
Aside from that, there have been only three six-month periods of above-average precipitation, the most recent being the one beginning November 1978.
The latest streak could come to an end in November, as drier-than-average conditions may prevail in the Midwest, especially in the first half of the month. If realized, this may boost the lagging corn and soybean harvests, allow farmers to prepare fields for next year before the winter, and give the soils a break before the next growing season. (tmsnrt.rs/36qqHWe)
HIGH MOISTURE, SLOW HARVEST
Midwest soil moisture in May hit the highest levels for any month in at least 30 years, and June and April were second and third in that time frame. Moisture levels have come down since then but remain elevated, and it has not been helpful for harvest.
As of Sunday, the US corn harvest was 41% complete, behind the five-year average of 61%. That is the fourth-slowest for the date in records back to 1981, behind 2009, 1992 and 1993.
Soybeans were 62% harvested as of Sunday, below the average of 78%. That is the seventh-slowest behind 2009 and five other years that were 1986 and earlier.
Last year’s growing season was much less stressful weather-wise for US farmers, though heavy rains slowed harvest and prevented a lot of pre-winter field preparation for the spring. Soils during the last three months of 2018 were among the top three wettest since 1989.
If November precipitation is not excessive, farmers may have a shot at fall fieldwork, assuming the ground does not freeze too early. But frozen fields are exactly what is needed in the Northern Plains.
In North Dakota, September rainfall was more than three times the normal rate and October more than two times above. Only 6% of corn and 29% of soybeans had been harvested there as of Sunday, severely behind respective averages of 41% and 91%. The only way equipment can enter the fields is if the ground stays frozen, and that is likely for the next couple of weeks.
Most of the Midwest is set for below-average temperatures in the first half of November, but the trend is less certain beyond that. Longer-range weather models suggest that warmer temperatures may return to the Midwest and Plains later in the month, possibly along with the wetter pattern.
WET IS LESS COMMON
Not only is the recent wet period unusual in length, but wet streaks are rare in general compared with dry ones. As previously mentioned, there have been only six periods since 1895 including the recent one in which precipitation has been above average in the Midwest for six consecutive months or longer.
However, there have been 16 periods since 1895 in which drier-than-average conditions persisted in the Midwest for seven months or longer. The record is 17 months of dryness between March 1930 and July 1931.
There was a 12-month dry stretch beginning in April 1953, and two 11-month periods, one beginning October 1933 and the other April 1976.
But the longer dry streaks have been notoriously absent in recent decades. The last dry stretch of seven months or more was the period between January and July 1988, which was a terrible year to grow corn and soybeans in the United States.
There have been three six-month stretches of dryness in the Midwest since then, the most recent being the one that began in April 2012, another disastrous year for crop yields.
Average precipitation levels in the Midwest have generally risen over the last several decades. Annual totals have risen more than 9% since the early 20th century. The US summer growing season, which is in full swing between May and August, is now 12% wetter, on average.
The largest monthly precipitation increases over that time frame have been observed in April and November, with jumps just over 18%. Only January and September have recently become drier in the Midwest than what was observed in the early 1900s.
Increasing precipitation in the Midwest over time may not explain why drier stretches have been more frequent over the past 125 years. The 17-month streak from 1930-1931 would have still stood if compared with its previous 30-year average rather than the 1981-2010 period, which is now customary in climatology. However, the precipitation deficit would be about 15% less severe.