I pointed out the hot spot in northern Minnesota in the contoured USHCN trends. There was a really interesting discussion of Minnesota sites by their state climatologist, JAmes Zandlo, in 2000, a couple of years ahead of Roger Pielke Sr’s investigations in Colorado. He showed the following contour for Minnesota (which prompted me to do a more general contour), the time-of-observation adjusted version is below, observing:
From Leech Lake Dam to Walker to Park Rapids (a total distance of less than 50 miles) the apparent changes per century are [TOBS - 3.19, 1.34, and -0.53; filnet adjusted - 2.92 to 1.57 to 0.36] respectively; … While it is generally found that global warming will be more pronounced in northern areas, it is difficult to understand how such a strong local variation in warming could be due to global climate change’.
Contour map of Minnesota USHCN TOBS trends. Leech Lake is the western station in the hot spot and the others are in a line to the SW. Other stations in the hot spot are Leech Lake and Pine River; Winnebigoshish is just to north (1.20)
Headwaters Corps of Engineers Sites
Zandlo did a thorough investigation of the sites, determining that the three sites in the hot spot were all at dams constructed by the Corps of Engineers in the early part of the 20th century. He reported:
The only 3 sites that have trends of +3 deg/century or more in the nonhomogenized data sets are all roughly within 50 miles of each other, all started in 1887, and all have been operated for the entire period by the Corps of Engineers at dam sites. It can be seen from the map HCN +’ Trends’ that all but 1 of the 6 stations with trends of 1.5 degrees or greater are all tightly clustered in that same vicinity. See Figure Map HCN +’ Trends’.
The Corps of Engineers sites in this northern Minnesota neighborhood all have zero or near zero homogenizing corrections for their entire records. The notations in the History files typically show station start and then no other entry at least until the 1950s.
From interviews with people familiar with the area, he reported the following:
- logging in the areas in and around the headwaters’ dams was already heavy early in the 2nd half of the 19th century and peaked early in the 20th century
- dams increased Leech/Winni/Pokegama areas from 173/117/24 sq.mi. to 234/161/45 sq.mi. for a 126 sq.mi. total increase from pre-dam conditions
- 1900-04: rotting dams were reconstructed, riprapping done at Winni
- 1902-04: dam tender residence at Leech built. Later, service building, barns, etc. were added. Apparently extensive floodplains no longer flooding (because of dam control).
- Congress approved money in the early-teens for straightening and improving’ the channel of the upper Mississippi River – work progressed into the 1920s
Zandlo showed the following picture of one site, asking the musical question:
What would happen to observed temperatures if the Weather Service required that each COOP site be paved with asphalt?’
There are notes about Leech Lake in the Appendix, including the following:
Preliminary examinations of other stations indicates that this pattern of large trends relative to non-HCN (typically more distant) stations and more modest trends relative to an HCN neighborhood appears to be most pronounced for the Corps of Engineers (COE) Headwaters’ stations…. Recall that most COE have essentially empty histories in the early years.
One relevant but difficult to use detail was a note found in the Leech Lake file which indicated that for long strings of days both the minimum and maximum temperature were identical at Winnibigoshish and Leech Lake dams. An exhaustive search for days with identical min and max values suggests that data sharing’ has occurred at other times for those two stations (see graph below).
July 1955 “All equipment had been painted this spring. The Thermometer support was repaired. Recording gage cleared and calibrated. A tree SE of the recording gage is getting quite big. I spoke to the observer about this and they are planning on doing some work around the gage.”
May 1964 Substation Inspection. “Exposure of the precipitation equipment at this station is [still?] poor due to tall trees, this was discussed with the obsvr, he advised me that he and his men had planned on moving the equipment about 100 feet west to get it more out in the open. He was asked to remember the date he moves the equipment.”
Sep 1966 Substation Inspection. “CRS is painted a silver color.”
Sep 1967 Substation Inspection. “Instrument shelter still painted a silver color. … Removed ⻠deg from the minimum thermometer. They had relocated the weather station equipment some time ago to avoid tree growth. … He advised that they had relocated the equipment the equipment some time ago, but could not remember the exact date. … began applying [white] paint to the shelter while we were still visiting
Oct 1968 Substation Inspection. “CRS found to be facing toward the south. Turned CRS to face north.”
Jun 1971 Substation Inspection. “CRS is in bad shape. Rotted and broken in spots. CRS is set in concrete. When new CRS arrives observer will install. He will break up and remove concrete at that time.”
Jan 1977 note in paper history file: some daily min and max data are identical to Winni
June 1983. First new site map since 1983[SM-?]. It appears that CRS has moved from N of precip in 1967 to East of it in 1983.
Here is a plot of the various versions for Leech Lake (Giss adjusted in bold red.) Thee are only two values for 2006 (which account fro the high close). Why are there no values after Feb 2006? Only the Shadow knows.
About this station in the hot spot, Zandlo observed:
Pokegama is the station with the largest slope among station time series corrected just for time-of-observation but it is essentially unaffected by the homogenizing process. It is perhaps germain to point out that Pokegama formerly held statewide daily record cold of —59 (Feb 1903). However, when data was examined at nearby stations, all were 17 to 21 deg warmer (Kuehnast, 1976) for that date. Notes on forms by editors (State Weather Service?) as late as 1905 state that minimum temperatures are considered unreliable’. Kuehnast believed that the thermometer at Pokegama was an exposed thermometer’ as called for by mid-19th century Smithsonian instructions.
Pine River is not specifically discussed by Zandlo, but oddly enough turns up as a type example in a preview article of the new USHCN calculations to be unveiled in July 2007 as an illustration of the new homogenization method. The article illustrates the old and new Pine River versions as below, with the new version notably lowering values in the 1980s.
For comparison, here is a compilation of the existing versions with GISS once again going only to Feb 2006 and USHCN as usual ending in Dec 2002. The closing uptick reflects only two months.
So what are we to make of this three sites? Zandlo identified them as anomalous but sort of left things hanging. No explanation is provided for the “gradient” between Leech Lake and Park Rapids, which prompted Zandlo’s discussion. Here’s a graphic for PArk Rapids which has a similar shape as Leech Lake but without the long-term increase in temperature:
It is inconceivable that there is a climatic reason for the difference between Leech Lake and Park Rapids? Is one “right” and the other “wrong”? How would one tell? Is it OK to just throw this data into a hopper and hope it’s OK? Or can non-climatic biases from these sites impart a bias to the overall record?