Warmer, Wetter Weather

Has Implications for Agriculture

By Tracy Sayler

University of Minnesota climatologist Mark Seeley says four weather trends in recent years are affecting northern agriculture: 1) warmer winters; 2) higher minimum temperatures; 3) greater frequency of tropical dew points; and 4) greater annual precipitation, with more frequent heavy rains and greater winter snowfall.

Seeley, a speaker at the recent Prairie Grains Conference, says that while weather over the long-term can be difficult to predict, looking back at weather over the long-term can establish trends. He says there are three drivers of observed climate patterns:

• Natural variability – these are the ‘usual’ factors that affect
  weather, including solar and orbital features, ocean currents, and jet stream patterns.
• Land use/landscape changes – urbanization, drainage, irrigation, deforestation.Greenhouse gases.

The warmer/wetter climate patterns bear out in weather statistics over the decades. For example, of the top 20 warmest January-March periods in Minnesota since 1895, based on aggregate mean temperature (F), 11 have occurred since the late 1980s. And looking at aggregate mean annual snowfall of 46 weather reporting stations in Minnesota, 41 show a positive (increased) snowfall trend from 1890-2001, of which 22 would be considered significant increases.  Only five showed a negative trend (less snow), none of which were significant.

Warmer and wetter holds true in the summer weather statistics over the years as well. There has been a slow but steady upward trend in summer dewpoints over the past century, and the number of intense precipitation events have increased. For example, 2” rains within 24 hours used to occur only about every two years.  However, in the last 15 years (1991-2005) Fosston, MN has had 15 occurrences of at least 2” rains; Pembina and Fargo in N.D. and Baudette, MN have had 16 occurrences, Fergus Falls, 19, and Hallock, Crookston, and Ada, 20.

There is one characteristic that the four climate trends have in common – water vapor, or the gaseous state of water.  And contrary to common belief, the greenhouse effect may have more to do with water vapor than gases such as carbon dioxide or methane. More needs to be understood about this link; however, new research technologies are now allowing climatologists to study the relation of water vapor to the greenhouse effect in more detail than the past, says Seeley.

Nevertheless, while the factors behind climate trends definitely need to be studied, so too do the implications of the climate trends. There have been 62 weather-related disasters costing $1 billion or more in the U.S. over the past 24 years (1980-2004). The cumulative economic consequence of these natural disasters, everything from hurricanes and floods to tornadoes and wildfires, is close to $400 billion. “What’s disturbing is that in 2005 alone the economic consequence of natural disasters was about $200 billion,” says Seeley. 

Seeley says the weather trends also have implications for agriculture and other areas of the economy, both good and bad:

Possible Implications of Warm Winters and Higher Minimum Temperatures

• Change in depth and duration of soil and lake freezing
• Longer outdoor construction season
• Change in overwinter survival rates of insect pests and plant diseases
• Reduced energy use for heating
• Change in animal migration, hibernation, and foraging
• Change in population dynamics of soil microbes

Possible Implications of Increased Frequency in Tropical Dew Points

• Dynamics of pathogen, insect, and microorganism populations
• Efficacy and persistence of herbicides
• Increased workload in heat related health care
• Feeding efficiencies and increased stress on livestock
• Increased demand for air conditioning

Possible Implications of a Wetter Climate

• Irrigation, drainage, runoff, and sediment management
• Change in storm sewer runoff design
• Mitigation of soil erosion
• Increased flooding potential
• Mitigation of blowing snow and management of roads and highways