Wednesday, August 24, 2011
Cornbelt Weather: It Is Always Changing. Right?
As the condition of the corn crop continues to decline, we find a note on the machine shed door that says, “Satan called and wants his weather back.” With several percentage points shifting out of good to excellent, and heading downhill to the fair and poor categories, we are reminded that the corn crop for much of the Cornbelt was planted and grew in adverse conditions. The weather in 2011, and for the past few years for that matter, seems to have been as volatile as the grain market. But are there any statistics to check out that curiosity?
Just like the dynamic moves in the commodity market, scientific data shows that weather is always changing. There have been many ice ages, and many warm spells, and on its way higher, temperatures can make some corrections and head down for a time. Whether Fibonacci numbers work on the weather remains to be seen, however Iowa State University’s Director of its Climate Science Program, Eugene Takle, has accumulated data that he says shows, “Climate change is much more than simply a rise in temperature. Other climate factors, specifically the frequency of extreme precipitation events, rise in humidity, and length of the growing season, are having much more impact on Iowa than changes in annual mean temperature.” His analysis is part of the August issue of the Ag Marketing Resource Center’s report on Energy and Climate. He has looked at several changes that are weather-related:
1) The humidity level in Iowa has risen for the past 35 years as indicated by the changing relationship between the dewpoint temperature and the air temperature. He says in Des Moines, the atmosphere has about 13% more moisture. Its presence fuels convective thunderstorms that provide summer precipitation. With the 3.5ºF increase in the dewpoint temperature, there is a higher probability of rain and lower probability of snow in the winter. He says that increases the recharging of winter soil moisture.
2) Takle says levels of stream have risen in recent years because of changes in precipitation. That has increased the potential for flooding in some regions. He notes that the capacity of the soil allows it to absorb 1.25 inches of rain over the course of a day, but more than that means increased runoff. He says the trend for increased rainfall points to 50% more water in the Mississippi River Basin over a 50 year period, if the prediction comes true in Iowa for a 21% increase in precipitation. Since the 1890’s, Takle says there has been a 57% increase in the number of days per year with more than a 1.25 inch rain in Cedar Rapids, and a 41% increase in Des Moines. In a related note, he says storm cells are more closely tracking with the direction of Iowa’s rivers, which have the potential to dump more water in the watershed and increase the flooding potential.
3) For the eastern part of the Cornbelt soil moisture has been the nemesis for farmers. Too much early and too little late. In Iowa, Takle says soil moisture has not been widely measured over long periods of time, but he says over the past 30 years it has “dramatically” increased. He points to the increase in drainage tile that has been installed in recent years to cope with the additional precipitation. He says one thought is that the large amounts of soil moisture has moved into the atmosphere and contributed to the higher humidity. While soil variations, slope, and subsurface conditions are complicating factors, Takle says the year to year variation of moisture will be more significant than long term trends.
4) Takle says wind speeds over Iowa and the US have been declining over the past 30 years. He says that is a negative for crops because it reduces ventilation and allows more heat stress, longer periods with dew (and that increases pathogen activity.) He is quick to say that the slower wind speeds are closer to the ground, and will not affect the energy output of wind farms.
5) In the Mississippi River Basin over the past 60+ years, Takle says the amount of sunlight reaching the ground has declined because of increased cloud cover. He quotes other researchers who say the trend is likely to continue because of increased levels of greenhouse gases.
6) On the issue of weather variability, Takle says the floods and droughts have the highest impact on the economy, and more research is needed to better understand the precipitation extremes. He says that includes why such extremes are increasing in frequency and whether they will continue.
Summary:
Many changes of Iowa’s climate over the last 30 years have had major economic impacts, some positive and some negative. Most notable are the annual rise in temperature, increase in extreme precipitation, and increase in humidity.
Posted by Stu Ellis on 08/24 at 12:00 AM | Permalink