In this post, I want to look at the rainfall that lead to this flooding from a climate perspective. The rainfall August 11-13, 1967 stands out as the highest of record for daily and multi-day totals. The only rainfall records this event does not hold are short duration records, which are all thunderstorm related. To set the stage, here is the background: the second half of July 1967 saw well above normal rainfall: 3.07" fell between July 16 and 31. That's still the fifth highest "second half of July" total. However, that was followed by a dry start to August: only 0.02" of rain fell during the first week of the month. But then the skies opened. Below is a plot of the hourly and cumulative rainfall for the week of August 8-15, 1967 (data extracted from Fairbanks August 1967 Local Climatological Data). More than half an inch of rain fell on the 9th. This was followed by about 36 hours with very little rain. Starting late in the afternoon on the 11th, moderate rain fell without much of a break until the morning of the 13th, though light rain continued to dribble on into the 15th before the fire hose finally shut down.
- 24 hour: 3.44" 11pm AKST August 11 to 11pm AKST August 12
- 36 hour: 4.40" 4pm AKST August 11 to 4am AKST August 13
- 48 hour: 4.76" 3pm AKST August 11 to 3pm AKST August 13
- Single calendar day: 3.42" August 12
- Two consecutive calendar days: 4.29" August 11-12
- Three consecutive calendar days: 4.98" August 11-13
Maximum 24-hour precipitation (not necessarily calendar day) has been recorded in Fairbanks since the Weather Bureau office opened in the summer of 1929. For two and three day totals, I've included the cooperative data from the Ag Experiment Station starting with 1915, when daily precipitation began to be regularly recorded. In the graphic below I show an example of the annual times series, in this case the maximum 24 hour precipitation (upper left) and then the GEV analysis for the annual maximum 24 hour precip (upper right) and annual maximum two and three day consecutive days (bottom row). The red line shows the fitted return period, while the open circles are the observations (which are plotted in rank order). I should point out that there is no significant trend in any of the annual values.
With 87 years of data:
- 3.44" in 24 hours is expected to occur on average once in 203 years
- 4.29" in two consecutive days is expected to occur on average once in 269 years
- 4.98" in three consecutive days is expected to occur on average once in 352 years
The GEV analysis I've presented here differs somewhat from that published in the 2012 NOAA Atlas 14 primarily in that I used a longer period of record (for extremes analysis, the longer the better), and, as near as I can tell, the maximum 24 hour precipitation (as distinct from calendar day) was not used in compiling that work.
The maximum 24 hour precipitation for August 1967 is listed as 3.42" in the August 1967 Local Climatlogical Data publication and has been carried through ever since. In fact the hourly precipitation data in the same publication shows that the correct amount is 3.44", 11pm on the 11th to 11pm on the 12th.