Forest Insect and Disease Newsletter

Do our trees have enough water?

image: Minnesota drought map 4/24/12

Drought monitor map April 24, 2012

Water enough to ward off opportunistic insects like bark beetles in pines, two-lined chestnut borer in oaks and bronze birch borers in birch this spring. In the forested parts of the state, most areas have been deficient in rainfall for the last ten months. With recent rains and wet snows, it's tough to know how much recharge the soils have gained versus the runoff that may have occurred.  MN Climatology website


Drought in Minnesota

Drought is defined as a period of abnormally dry and/or unusually hot weather sufficiently prolonged for the corresponding deficiency of water to cause a serious hydrologic imbalance. When a serious hydrologic imbalance occurs, soil moisture reserves, groundwater supplies, lake levels and stream flows are negatively influenced. Water-dependent industries including agriculture, public utilities, forestry, and tourism are profoundly affected.

Nearly all of Minnesota is currently undergoing drought.


Overview

Many Minnesota counties are designated as undergoing Moderate to Severe drought. In northeast Minnesota, the drought is due to the lingering impact of precipitation deficits accrued during the 2010 growing season and spotty rainfall in 2011. Elsewhere around the state, significant late-summer and autumn 2011 precipitation shortfalls led to rapidly deteriorating hydrologic conditions.

Precipitation totals for the eight and one-half month period from August 2011 through mid-April 2012 fell short of the historical average by more than six inches for much of the southern one-third of the state and portions of northeast Minnesota (maps below). When compared with the same multi-month period in the historical database, the precipitation totals ranked among the lowest on record in some southern Minnesota counties.

Precipitation totals for the two and one-half month period from February 1, 2012 through mid-April 2012 exceeded the historical average by more than one inch in many counties (maps below). Much of this precipitation fell after the soils thawed, thus leading to topsoil moisture recharge. Nonetheless, subsoil moisture content remains deficient due to the long-term precipitation  deficits. Water levels on many lakes, rivers, and wetlands also remain below average.

 

Multi-month precipitation maps

image: Total Precipitation departure from normal image: Total Precipitation map image: Total Precipitation Historical Rank
image: Minnesota Map total precipitation departure from normal image: Total Precipitation map image: Total precipitation historical rank map