For the People and Wildlife of the Northern Great Plains, Heavy Winter and Spring Precipitation Brings a Taste of the Future

WWF's Northern Great Plains region stretches from Northern Nebraska northward through Eastern Montana and Western North Dakota and into Canada. It has been an exceptionally wet Winter and Spring for the area. As the first figure below indicates, precipitation in November 2010-April 2011 ranked 112^th out of 116 years in the National Oceanic and Atmospheric Administration (NOAA) North West Central Region (Nebraska, Wyoming, South and North Dakota, Montana), making it the 5^th wettest November-April period on record. As the second image indicates, it has been especially wet in eastern Montana, which from 28 February through 28 May received over 150-300% of normal precipitation for the period.

Above: Nov 2010 - April 2011 regional precipitation rankings relative to precipitation for the same period over the 116 year record.

Above: Much of eastern Montana from 28 February through 28 May received over 150-300% of normal precipitation for the period.

From 1 May through 29 May, the city of Billings, Montana, received 9.16 inches (23 cm) of rain, 6.84 inches (17.4 cm) above normal -- and still more rain fell on 29-30 May. In one 24-hour period (straddling 24-25 May) alone, the city received 3.35 inches (8.5 cm)of rain. On 26 May, with 6 days left in the month, the National Weather Service announced that May 2011 already was the wettest month ever recorded in Billings. The wettest month previously was May 1981, when 7.71 inches (19.6 cm) fell.

Among the consequences of the heavy precipitation were record snowpacks in parts of the state. As temperatures have warmed, heavy rains and melting snow are producing widespread flooding across the state, with many rivers seeing the highest May flood crests on record (see Preliminary May Flood Crests, National Weather Service Forecast Office, Billings Montana, 26 May 2011).  For example, as the figure below indicates, the Musselshell River crested at 14.75 feet (4.5 meters) in late May, well beyond the previous record of 12.9 feet  (3.9 meters) set on 22 June 1975. 

Impacts

Anne Schrag, Climate Adaptation Program Officer for WWF’s Northern Great Plains Program describes the consequences of the deep snow for some of the region’s wildlife this winter:

“Deep snow had a significant impact on wildlife and livelihoods in the Montana Glaciated Plains, a priority landscape for WWF’s Northern Great Plains Program.  One species of conservation concern, pronghorn antelope, have small hooves that are not suited to deep snow.  Thus, they search out areas that are snow-free, such as railroads and roadways.  This behavior led to 270 pronghorn being killed in a single collision with a train this past winter.  Hundreds more have also been found lying dead along railways.  Biologists have speculated that the size of the herds in this area may have declined by 50%.  This is sure to take a toll economically as well, since this area is one of the premiere pronghorn and large ungulate hunting regions in the state.

Just west of the [WWF’s Northern Great Plains] priority region, in the northern Rockies, up to 90% mortality rates have been found in mule deer populations, compared with 20% during normal years."

As the snow melts and is augmented by heavy rains, the impacts grow and become more serious for people and communities. Schrag continues:

“… flooded fields are pushing back planting times for farmers; rivers, creeks and streams running above their banks are threatening livestock and property (some cows and horses have been found dead in the area, possibly due to harsh winter conditions); the potential for increased mosquito populations brings with it an increased threat of West Nile virus.”

Flooding has not been confined to rural areas. Some communities such as Roundup on the Musselshell River have suffered serious damage as flood waters course through low-lying areas and into houses, commercial buildings and other structures (see video below). The widespread impacts compelled Montana Governor Brian Schweitzer to declare on 22 May a statewide emergency.

The Climate Connection

Is this evidence of climate change or natural variability?  The answer is that it most likely is both.  According to Global Climate Change Impacts in the United States(2009), a major assessment from the U.S. Global Change Research Program, precipitation has increased in the northern Great Plains over the last several decades. Precipitation is increasing, particularly in the winter and spring. The figure below shows a the long-term trend of increasing precipitation for the West North Central region from March through May 2010 – even before March-May 2011.

More significant is the increase in extreme precipitation events, not just in the Northern Great Plains but nationwide.  The figure below shows the Climate Extreme Index for extreme 1-day precipitation events in Spring, indicating that over the last half century there has been a marked increase in the percentage of the U.S. getting a much greater than normal portion of its precipitation from extreme 1-day events in Spring.

In Billings, for example, more than one third of the rain that fell from 1-29 May this year came on a single day: on 24 May, the city recorded 3.12 inches of rain, an all time daily record for Billings.  According to the National Weather Service, the previous record was 2.91 inches et on 8 June 1997.

Above: The Climate Extreme Index (CEI) "Step 4" for Spring 1910 through 2010 (excluding Spring 2011, for which data is not yet available).  According to the definition, CEI Step 4 is "[t]wice the value of the percentage of the United States with a much greater than normal proportion of precipitation derived from extreme (equivalent to the highest tenth percentile) 1-day precipitation events."

According to Global Climate Change Impacts in the United States:

"Flooding often occurs when heavy precipitation persists for weeks to months in large river basins.  Such extended periods of heavy precipitation have also been increasing over the past century, most notably in the past two to three decades in the United States."

And what about the future? Global Climate Change Impacts in the United States says elevated and increasing concentrations of greenhouse gases in the atmosphere are projected to drive a continuation in these precipitation trends in the Northern Great Plains, particularly in the winter and spring.  Nationwide, the study says:

"For the future, precipitation intensity is projected to increase everywhere, with the largest increases occurring in areas in which average precipitation increases the most...The magnitude of the projected changes in extremes is expected to be greater than changes in averages, and hence detectable sooner."

What do we do?  Only by sharply reducing greenhouse gas emissions can we slow the pace of climate change enough to substantially enhance our long-term prospects for adapting to disruptive impacts.  Meanwhile, we must prepare for the impacts that already are emerging and that will continue to grow. The  most elemental step in preparing ourselves for an era of climate disruption is to recognize that it no longer is appropriate to assume that climate is unchanging.

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