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Earlier seasonal snowmelt runoff and increasing dewpoints - Upper Midwest

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  • npat1@juno.com
    I am a hydrologist living in Chanhassen, Minnesota. I am one of the concerned scientists that gave signature approval for: A Letter From U.S. Scientists The
    Message 1 of 1 , Oct 15, 2003
      I am a hydrologist living in Chanhassen, Minnesota. I am one of the
      concerned scientists that gave signature approval for:

      A Letter From U.S. Scientists
      The State of Climate Science: October 2003

      I received notice earlier this month that over 1000 scientists gave their
      signatures in support of the Letter on climate change.

      I am asking scientists that signed the Letter and other people to take a
      look at my final draft paper that I will be presenting at the National
      Weather Service (NWS) - Climate Prediction Center (CPC) Workshop in Reno,
      Nevada: 20-23 Oct 2003.

      If you choose to take a look at my final draft, I would appreciate seeing
      any comments you may have. I would appreciate your support. At this
      date, I am still uncertain on whether or not my employer (NWS North
      Central River Forecast Center) is supportive of my effort on this paper.
      The narrative portion of my paper is on the Minnesotan's For
      Sustainability (MFS) website.

      The MFS website is:

      The narrative of my paper on the MFS website is called: "Snowmelt &
      Dewpoints in Minnesota, Wisconsin, and North Dakota". The URL for my
      paper is:


      If you would like to view the figures and tables that go with the paper
      please send me an e-mail message to [ npat1@... ].

      The figures and tables are in Excel format. I can forward the Excel
      spread sheets or I could fax or mail the printouts from the figures (4)
      and tables (2).

      I believe that Figure 1 on earlier snowmelt runoff for three major
      headwater rivers is very telling on climate change.

      I would appreciate any comment that people may have on my paper and work.

      A copy of the narrative is included below, copied from my paper on the
      MFS website.


      Affiliation is for identification purposes only

      Patrick J. Neuman (Pat)
      Senior Hydrologist
      National Weather Service
      North Central River Forecast Center (NCRFC)
      Affiliation is for identification purposes only

      NCRFC is collocated in Chanhassen, MN (along with the NWS Weather
      Forecast Office for east central Minnesota and northwest Wisconsin, and
      the National Operational Hydrologic Remote Sensing Center).

      The narrative paper that follows is from the website at:

      Earlier in the Year Snowmelt Runoff and Increasing Dewpoints for Rivers
      in Minnesota, Wisconsin and North Dakota

      Patrick J. Neuman, Snow Hydrologist, NWS, NCRFC

      September 11, 2003

      I. Abstract
      II. Snowmelt physics
      III. Hydrologic area and data sources
      IV. Timing of annual snowmelt runoff
      V. Average monthly dewpoint
      VI. Conclusions on the timing of snowmelt runoff and humidity
      VII. Air temperatures
      VIII. Additional discussion
      IX. Recommendations
      X. References

      I. Abstract

      Daily river flow data were used to evaluate the timing of snowmelt runoff
      at three river stations within the Northern Great Plains and Upper
      Midwest. Timing of snowmelt runoff is shown by a X-Y plot using 10 year
      moving averages for �Annual Beginning Day of Snowmelt Runoff� at the
      river stations for 1910-2003. Average dewpoint plots are shown for three
      climate stations near the river stations. The plots show monthly January
      - April dewpoint for 10 year moving averages for 1948 to 2003. A
      discussion of snowmelt physics is included, describing how humidity as
      measured by dewpoint affects the rate of snowmelt. Based on the study
      results, shown by the plots on the timing of annual snowmelt runoff and
      by plots of dewpoint averages at climate stations, conclusions are
      reached, and recommendations are given.

      II. Snowmelt Physics

      After a long period of cold weather, a snowpack can absorb large amounts
      of heat before thaw occurs. Once the temperature of the snowpack reaches
      zero degrees Celsius throughout, liquid water starts forming within the
      snowpack. When the liquid water exceeds a threshold (about 15 percent of
      total snowpack water equivalent), snowmelt begins.

      Solar radiation is the dominant energy transfer for snowmelt during clear
      sky periods. Usually snowmelt occurs on south facing slopes and hilltops
      before snowmelt occurs on north facing slopes and other parts of the
      basin. In winter and early spring, sun angles are low and days are
      short; thus snowmelt from solar radiation alone during this period is
      usually gradual and intermittent.

      The significance of latent heat for snowmelt has been described by Dunne
      and Leopold (1978):

      �If water from moist air condenses on a snowpack, 590 calories of heat
      are released by each gram of condensate. This is enough energy to melt
      approximately 7.5 gm of ice, which when added to the condensate yields a
      total of 8.5 gm of potential runoff�.

      Latent and sensible heat transfers can result in high snowmelt rates, as
      warm moist air moves into a region. Latent and sensible heat transfers
      can cause rapid snowmelt from all parts of a basin simultaneously, day
      and night, even during winter. Warm temperatures, high humidity, and
      strong winds have large effects on the rate of snowmelt. In comparison,
      heat supplied by rainfall is usually minor, unless a warm rainfall of
      long duration occurs. A more detailed description of equations for
      snowmelt are given by Price and Dunne (1976).

      Dunne and Leopold (1978) show that �highest melt rates were associated
      with the warm sector of a large weather disturbance� (Quebec, May of
      1973). For the last three days of an eight day melt of the snowpack in
      May of 1973 (Quebec), melt due to latent heat was shown to be nearly
      equal to melt from net radiation, and melt from latent heat during the
      last three days was shown to be around 50 percent of the melt due to
      sensible heat transfer from atmospheric convection (mixing).

      From the theoretical and physical descriptions given above, it is clear
      that the rate of snowmelt increases as humidity increases, due to latent
      heat released as water vapor condenses when air temperatures are above

      III. Hydrologic Area and Data Sources

      The National Weather Service (NWS) North Central River Forecast Center
      (NCRFC) is responsible for hydrologic forecasting for rivers in the Upper
      Midwest and parts of the Northern Great Plains. NWS hydrologic models
      and NCRFC calibrated snow and soil moisture/runoff model parameters are
      used in forecasting snowmelt runoff flow into the rivers, lakes, and
      reservoirs (Neuman, 1999).

      River stations selected for this study, which are within the headwaters
      of three of the major basins of North America, include:

      Red River at Fargo, ND, headwaters to Hudson Bay
      St. Louis River at Scanlon, MN, headwaters to Lake Superior
      St. Croix R. at St. Croix Falls, WI, headwaters to Mississippi River

      The river stations were chosen based on:

      1) quality flow data from the early 1900s to current;
      2) annual snowmelt runoff nearly every year;
      3) location within the Upper Midwest and Northern Great Plains; and
      4) author's experience & expertise gained working in hydrology in
      Midwest and Great Plains.

      Hydrologic characteristics of the river basins, terminology, and study
      methodology are outlined in Table 1 (work sheet for Figure 1, discussed

      Source of mean daily flow data was the United States Geological Survey
      (USGS). Source of dewpoint data was the Midwest Regional Climate Center

      IV. Timing of Annual Snowmelt Runoff

      Mean daily flows were used in this study to determine �Annual Beginning
      Day of Snowmelt Runoff� for years from 1910 through 2003 at the three
      river stations. The methodology is explained in Table 1 (work sheet for
      Figure 1).

      Figure 1 shows 10 year moving averages for annual beginning day of
      snowmelt runoff at the river stations. The 10 year moving averages for
      Julian Days (each Julian Day representing the beginning date of snowmelt
      runoff for a year at a river station) are plotted on the 10th year of the
      10 year moving Julian Day averages.

      The data on Figure 1 show trends for recent earlier in the year annual
      snowmelt runoff at the river stations, that began during the 1960-1980
      period, and became more evident during 1981-2002 period.

      V. Average Monthly Dewpoint

      Climate stations that are within or near the three river basins include:

      Fargo, North Dakota (within Red River basin)
      Duluth, Minnesota (southeast of St. Louis River basin)
      Eau Claire, Wisconsin (southeast of St. Croix River basin)

      Monthly January to April dewpoint (10 year moving averages), based on
      1948-2003 monthly averages, are shown in figures 2-4. The figures show
      recent increasing dewpoint trends for January, February, and March 10
      year moving averages, but no trends for April monthly dewpoints.

      VI. Conclusions on the Timing of Snowmelt Runoff and Humidity

      1) Trends were shown for recent earlier in the year annual snowmelt
      runoff at three river stations within the Northern Great Plains and Upper

      2) Trends were shown for recent increasing dewpoint averages for January,
      February, and March but not April.

      Other factors besides humidity are important in affecting snowmelt,
      including air temperatures, wind speeds, temperature of precipitation,
      ground temperatures, extent of snowpack over the entire Great Plains and
      Midwest and its albedo (characteristics of the snow cover in reflecting
      solar radiation).

      VII. Air Temperatures

      Based on snowmelt physics, historical modeling, and real time operations
      involving snowmelt and snowmelt runoff, air temperatures and humidity are
      likely the most significant factors affecting the rate of snowmelt.

      Thus some investigation and reporting on air temperatures is warranted
      with respect to snowmelt. �The largest increases in both temperatures
      and humidity for the Northeast, Midwest, and Northern Great Plains have
      been during Winter and early Spring months� (Neuman, 2003). The report
      by Neuman (2003) included selection of temperature stations and analysis
      and summaries of mean air temperature and dewpoint data for many stations
      in the Midwest and Northern Plains. In an investigation and report on
      the climate in the Great Lakes region, from a study that was entirely
      independent from the work and report on the Northeast, Midwest, and
      Northern Great Plains by Neuman (2003), the Kling (2003) concluded for
      the Great Lakes region that:

      �In the past four years, ..., annual average temperatures have ranged
      from 2 to 4� F (1 to 2� C ) warmer than the long-term average and up to 7
      �F (4� C) above average in winter.�

      The conclusions on temperatures by Kling (2003) and Neuman (2003) were in
      agreement, even though the work was done independently.

      VIII. Additional Discussion

      From the snowmelt physics discussion in Section II, it is clear that
      humidity and the rate of snowmelt are connected, with increases in
      humidity resulting in additional heat transfer from the latent heat of
      condensation as water vapor condenses on a snowpack of 0 degrees Celsius,
      when air temperatures are above freezing. The process can be shown
      theoretically but would require considerable work to demonstrate
      experimentally or with operational hydrologic and meteorological data.
      This work has shown the trend for earlier snowmelt runoff in recent
      years, and the trends for higher dewpoints in recent years, but this work
      has not proven that the higher average dewpoints have caused the earlier
      in the year recent annual snowmelt runoffs.

      Mean daily flow records that were used in the evaluation of the timing of
      snowmelt runoff for the river stations in this study range from 1902 to
      current, a period of 105 years of record. However, monthly dewpoint data
      for this study was only available from 1948 to current, only 55 years of
      record. Although figures 2-4 indicate trends for recent increasing
      monthly dewpoint averages for January, February, and March, the 55 years
      of record may be insufficient for making firm statements regarding long
      term trends in average dewpoints.

      However the river flow data records, with 105 years of record, show the
      timing of annual snowmelt runoff for years that preceded the dewpoint
      records used in this study. In other words, the river flow data used in
      the evaluation of the timing of annual snowmelt runoff for 1902 through
      1947, infer the effects of temperatures and humidity for the period 1902
      through 1947.

      In viewing Figure 1, the 1920s to early 1950s period had earlier annual
      snowmelt runoffs than the late 1950s and 1960s period. However, the
      period from the mid 1980s to the snowmelt runoff period in 2003 had the
      earliest annual snowmelt of record, substantially earlier than the 1920s
      to early 1950s period. An evaluation of mean annual dewpoints at
      Minneapolis, MN from1918 to the 1940s, which were calculated from mean
      annual relative humidity and annual air temperature data (Table 2.) shows
      that 5 year annual dewpoint averages for 1998 through 2002 exceeded all
      previous 5 year averages at Minneapolis since the beginning of record for
      calculated annual dewpoint averages (1918).

      IX. Recommendations

      The recent trends shown in this study for earlier annual snowmelt runoff
      at river stations within the Upper Midwest and Northern Great Plains, and
      for increasing January - April dewpoint averages call for:

      1) Review of NWS hydrologic models used by NCRFC in modeling snowmelt

      2) Review of NCRFC snow and soil moisture model parameters used in
      models by NCRFC in issuing hydrologic forecast products with the NWS
      Advanced Hydrologic Prediction System (AHPS). AHPS is described by
      Deweese (2002).

      X. References

      Deweese, M.M.. (2002) AHPS Procedures and Products at the NCRFC <
      http://www.crh.noaa.gov/ncrfc/WebShows/AHPSRfc/sld001.htm >.
      Dunne, T., Leopold, L.B. (1978) Water in Environmental Planning; pp.
      Kling, G.W. et. al. (April, 2003) �Confronting Climate Change In the
      Great Lakes Region <
      http://www.ucsusa.org/greatlakes/glchallengetechbac.html >.
      Neuman, P.J.(1999) Hydrologic Forecast Procedures & Spring Flood
      Outlooks, Upper Midwest <
      http://www.crh.noaa.gov/ncrfc/documents/Papers/Outlooks/Outlooks.htm >.
      Neuman P. J. (April, 2003) Special Report � Air Temperatures & Dew
      Points, Great Lakes States <
      http://www.mnforsustain.org/mn_dewpoints_neuman_p_special_report.htm >.
      Used with permission of the author.

      Please send mail to webmaster@... with questions or comments
      about this web site. Minnesotans For Sustainability (MFS) is not
      affiliated with any government body, private, or corporate entity.

      Pat Neuman
      Chanhassen, MN

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