Dry Spells during a Wet Cycle

 Are we currently too wet, too dry, or just right?

Since the early 1990's the Red River Valley and Devils Lake Region has been in a prolonged wet cycle. This wet cycle has resulted in record flooding throughout the Red River Basin, and back-to-back-to-back major flood episodes along the mainstem Red River.  Years of excessive precipitation have pushed both Devils Lake and Stump Lake up by nearly 30 feet, and have brought about several billions of dollars in damage to public roads, infrastructure, private property and farmland across the combined Red River and Devils Lake Basins. While such prolonged periods of above normal precipitation are noted in the historical record, this particular wet cycle is the longest observed since the late 1880s.

Yet, since this past September there has been a noted decrease in rainfall across the region, and when combined with a warmer than average fall period, this has yielded preliminary drought conditions. According to the U.S. Drought Monitor, Abnormally Dry conditions are widespread across the Red River Valley and portions of west central Minnesota are experiencing Moderate Drought conditions. While these drier conditions are certainly a welcome relief to most folks, many are wondering just how unusual is this dry spell, and does it mean the our wet cycle has ended?

Historically, precipitation in the Red River Valley and Devils Lake Basin ranges from 10 to 30 inches in any given year,with about 20 inches being the rough long-term average. Based on the predominant land use within the region (agriculture), the make up of the river system (hydrology) and variances in precipitation (meteorology/climatology) eastern North Dakota and northwest Minnesota are never very far from one extreme or the other, drought or flood.  In other words, there are three ways of looking at drought or wet cycles - Hydrologically, Agriculturally or Meteorologically. Currently, the area is in a short term climatological drought, the beginning stages of an agricultural drought, yet still in generally wet hydrological conditions.

The current dry period is part of our natural climate variability as well as a classic response to this seasons active La Nina pattern. Based on the history of northern plains fall seasons, La Nina falls tend statistically towards drier than average. To this extent, the fall of 2011 is simply a "typical" response of the global circulations to the La Nina. Will this dry period last? The short answer is probably not.

According to the Official Climate Outlooks from our NWS Climate Prediction Center (CPC), the most likely scenario for the winter of 2011/2012 is one of colder and wetter than average conditions. This is based on the typical impacts of the La Nina, as well as the intra-seasonal variability produced by the Arctic Oscillation, North Atlantic Oscillation, the Madden-Julian Oscillation and other forcings. That all means that while the upcoming December through February time frame will most likely average colder and wetter, there will still be some periods of dry and mild weather. However, the impacts of La Nina do suggest more frequent cold snaps and a greater than normal risk of significant snow events yet to come.

Beyond this winter season, the CPC suggests that colder and wetter is the most likely scenario to continue into the spring of 2012, much like this past early spring period.

Looking even farther into the future, the large scale climate signals suggest a continuation of the past decades wet cycle. According to the U.S. Global Change Research Program (USGCRP) the area will likely see increases in temperature and precipitation. To quote the assessment "... The likely increase in precipitation in winter and spring, more heavy downpours, and greater evaporation in summer would lead to more periods of both floods and water deficits. The projected pattern of increasing precipitation in winter and spring and heavy downpours is expected to lead to more frequent flooding, increasing infrastructure damage, and impacts on human health. Heavy downpours can overload drainage systems and water treatment facilities, increasing the risk of waterborne diseases. In summer, with increasing evaporation and longer periods between rainfalls, the likelihood of drought will increase and water levels in rivers and wetlands are likely to decline." 

How about the more recent history of the region? Periods of prolonged below median precipitation have occurred with some regularity since the overall wet cycle began in 1993. As an example, significant dry spells occurred in the fall of 2003, the spring of 2005, the summer of 2006 ('Flash Drought'), the spring of 2007 and most recently the spring of 2008. Even during these brief dry periods, some areas - most notably the far southern Red River Valley - remained nominally wet.

In light of the current climate outlooks, the dry weather of late is not likely to last. Based on the outlooks from the CPC, as well as local research, as we get towards the Thanksgiving Holiday period on into December, La Nina begins to strongly influence the 'weather' over the northern plains. While it is not possible to predict individual storm events, the greatest threat for significant storms during a La Nina influenced winter season is yet to come.

Below are some graphics, courtesy of the U. S. Drought Monitor, depicting the extent of recent droughts in North Dakota and Minnesota. Also, data from Fargo and Grand Forks show the variability in precipitation that is common.   

Click for larger image

The image above represents drought conditions during the fall of 2007 across Minnesota. The top left panel shows the extent and intensity of drought conditions on September 18th 2007; the upper right is November 1 2011 drought conditions. The lower panel is a time series from January 2000 through November 2011, with the relative areal extent of drought conditions across Minnesota. Click for a larger image. Image courtesy U.S. Drought Monitor.

The image above represents drought conditions during the fall of 2007 across North Dakota. The top left panel shows the extent and intensity of drought conditions on August 1 2006; the upper right is November 1 2011 drought conditions. The lower panel is a time series from January 2000 through November 2011, with the relative areal extent of drought conditions across North Dakota. Click for a larger image. Image courtesy U.S. Drought Monitor

The graph above represents the yearly total (Climate Division Average) rainfall for ND Climate Division #6, which encompasses east central North Dakota. The blue line is the total average rainfall, the red line is a 5 year running average. Note that the period from 1970 - 1988 represents and average annual rainfall across the region of just under 20 inches per year. After the 1988 period, the total average annual rainfall increased to over 22 inches, with the past decade averaging over 23 inches. Note the relative dry period in 2006. Image based on data courtesy High Plains Climate Center Acis

 

The graph above represents the yearly total rainfall for the Fargo/Moorhead area. The blue line is the total average rainfall, the red line is a 5 year running average. Note that the period from 1970 - 1988 represents and average annual rainfall across the region of just under 20 inches per year. After the 1988 period, the total average annual rainfall increased to over 22 inches, with the past decade averaging over 24 inches. Note the relative dry period in 2003 and 2006. High Plains Climate Center Acis



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