Iowa Much Hotter In 1936

By Paul Homewood

 

http://www.ncdc.noaa.gov/sotc/national/2012/13/supplemental/page-7/

 

The 1930’s create a big problem for NOAA, in their attempts to portray the current climate as “extreme” and “unprecedented”. As a result, they often resort to distortion and deception in order to lessen the significance of those years. And often with success, I might add. Hence the reaction of one commenter, a few days ago, who did not believe it could have been “so damn hot” in the 1930’s.

Fortunately though, we do still have access to the original records from that time. Using these, I have already shown that the summers of 1934 & 1936 were much hotter than last year in Oklahoma, Kansas and Ohio. In this post, I am going to take a closer look at Iowa, but this time analysing state wide trends, rather than individual stations. As can be seen in NOAA’s map above, Iowa appears prominently in the number of days =>100F in 2012.

I will be comparing the month of July 1936 with the same month last year. (As in most years, July last year was much the hottest month of the summer). The information to follow is based on the State Climatological Reports, which can be downloaded here.

 

 

 

First let’s look at some of the headline numbers.

1) According to NCDC, July temperatures in Iowa were the 3rd highest on record, with a mean of 79.7F, compared to 82.7F in 1936, and 81.7F in 1901. (Yes, that’s right, back before global warming had started!) It is also worth pointing out that the summer as a whole in 2012 was only the 9th warmest in Iowa, so it is appropriate to concentrate just on July.

2) As the above report makes clear, July 1936 was exceptional, with mean temperatures 8.8F higher than normal. However, according to the July 1936 report, the mean temperature was 83.4F, 0.7F higher than NCDC are now declaring. (More on this later).

3) The record temperatures in July followed a very cold winter. As the report declares:-

As a result, the annual temperature for 1936 was “extremely” average, 70th warmest since 1895. Most people would regard severe cold followed by severe heat as the epitome of “extreme weather”. But not according to the NCDC’s “US Climate Extremes Index”, which cancels out the cold and heat, and says 1936 was a pretty normal year.

4) The total number of days, with maximum temperatures 100F or over, averaged over 113 stations, was 16.9.

5) The highest temperature recorded in 1936 was 117F at Logan, just one degree lower than the 118F set in Keokuk during 1934. (The latter is still the all time record for Iowa). The highest set in July 2012 was just 107F.

6) The hottest afternoon Iowa as a whole ever experienced was on July 14, 1936, when the average maximum temperature at 113 stations was 108.7F.

 

Comparison with 2012

There is no question that 1936 was a brutal summer in Iowa, but how does it compare with 2012? Indeed, is there any comparison at all?

There are currently 194 stations that contribute to the calculations of Iowa state temperatures, though maybe up to a third don’t regularly contribute. Of these, 31 were operating in 1936. These stations are split into 9 divisions, which are designed to be “as climatically homogenous as possible”. Divisional averages are calculated, and these are then used to calculate statewide temperatures, based on geographical area weightings.

Fortunately the same divisions, that are in use now, were also in use in 1936, so it is possible to make like for like comparisons. Using these 31 stations, and building up divisional averages, we can compare 1936 directly with 2012. (The full station lists and calculations are in the Appendix).

Let’s look at the number of days which were 100F or over, averaged over the whole of the State.

 

Year	Days =>100F
1936	16.3
2012	3.7

 

And now the statewide average maximum temperatures for the month.

 

Year	Av Max Temp
1936	98.5
2012	92.4

 

However hot it was in Iowa last year, it is clear that conditions then do not even begin to compare with the summer of 1936, in terms of either length or severity of the hot weather. And remember, this is all before factoring in any potential UHI effects.

 

Maximums & Minimums

Although maximum temperatures were 6.1F higher in 1936, means were only 3.0F higher, (or 3.7F depending whose figures you believe). This suggests that night time minimums would have been about the same for the two years. This, of course, is not the first time this has been noted.

Two possible reasons for this dichotomy could be:-

1) Greater humidity in 2012. If this were so though, it would suggest that the drought last year was not as severe as the PDSI indicates. In other words, evaporation should not be as great.

2) UHI effect – higher night time temperatures are a classic symptom of this.

 

Given that July rainfall totals were negligible in both years, it seems unlikely that differences in cloud cover could be a factor.

 

NCDC Versus State Reports

As mentioned above, the latest NCDC figures show a mean temperature of 82.7F for July 1936, whereas the original state report showed 83.4F, a difference of 0.7C.

Curiously, I found a similar discrepancy, when I was comparing temperatures in Virginia. At the time I asked Deke Arndt at NOAA to show how they built up the 1934 figures in the current dataset, and why they differed to the original reports. He admitted that he had no clue.

So what is going on? It has been claimed previously that changing mixes of stations may be responsible – for instance, inclusion of a greater proportion of high altitude stations in Arizona would clearly pull down state averages, and would consequently need to be allowed for.

But I don’t see how this argument could be used in Iowa, as the current system of climate divisions was also in use in 1936.

This issue can only be resolved by NCDC publishing all of their calculations for earlier years, and reconciling all differences.

 

Conclusions

OK, this is just one month, in just one year, in just one state. But it helps to fill in the picture of how things really were in the 1930’s. Next time someone tries to persuade you that the 1930’s really were not so hot, point out that they are talking through their hat.

 

 

 

APPENDIX

 

 

DIVISION	DAYS 100F+			AVERAGE MAXIMUM
	1936	2012		1936	2012
NORTHWEST 01
LAKE PARK	12	8		96.3	94.6
POCAHONTAS	17	0		99.3	90.5
ROCK RAPIDS	19	1		100.2	91.7
NORTHWEST AVERAGE	16	3		98.6	92.3
NORTH CENTRAL 02
ALGONA	14	0		97.2	89.2
CHARLES CITY	12	0		94.1	90.2
MASON CITY	13	0		96.3	89.1
NORTHWOOD	9	0		94.2	87.0
NORTH CENTRAL AVERAGE	12	0		95.5	88.9
NORTHEAST 03
DECORAH	14	3		96.0	92.4
DUBUQUE	13	4		94.6	91.8
ELKADER	13	1		95.3	89.3
NORTH EAST AVERAGE	13	3		95.3	91.2
WEST CENTRAL 04
CARROLL	20	4		100.4	92.4
GUTHRIE	20	5		100.3	93.9
SIOUX CITY	20	6		100.2	94.1
WEST CENTRAL AVERAGE	20	5		100.3	93.5
CENTRAL 05
AMES	16	1		97.8	91.5
DES MOINES	17	5		99.1	93.5
GRINNELL	16	2		99.2	90.5
IOWA FALLS	14	1		98.1	89.8
MARSHALLTOWN	15	3		97.6	91.3
CENTRAL AVERAGE	16	2		98.4	91.3
EAST CENTRAL 06
BELLE PLAIN	15	2		97.6	90.7
DAVENPORT	13	3		97.1	90.9
EAST CENTRAL AVERAGE	14	3		97.4	90.8
SOUTH WEST 07
ATLANTIC	19	4		102.5	94.0
SHENANDOAH	20	7		100.8	95.7
SOUTH WEST AVERAGE	20	6		101.7	94.9
SOUTH CENTRAL 08
ALBIA	19	6		100.3	94.1
CRESTON	15	3		99.2	94.0
KNOXVILLE	17	7		99.6	95.2
LAMONI	16	8		98.5	95.5
WINTERSET	21	6		100.8	94.1
SOUTH CENTRAL AVERAGE	18	6		99.7	94.6
SOUTH EAST 09
BLOOMFIELD	22	7		101.9	95.3
BURLINGTON	18	4		100.2	93.3
FAIRFIELD	19	13		101.8	96.9
KEOKUK	17	7		99.0	95.1
SOUTH EAST AVERAGE	19	8		100.7	95.2

 

			WEIGHTED			WEIGHTED
DIVISION	AREA	WEIGHT	DAYS 100F+			AVERAGE MAXIMUM
			1936	2012		1936	2012
1	6850	0.1217	1.9	0.4		12.0	11.2
2	6096	0.1083	1.3	0.0		10.3	9.6
3	6597	0.1172	1.6	0.3		11.2	10.7
4	7368	0.1309	2.6	0.7		13.1	12.2
5	7357	0.1307	2.0	0.3		12.9	11.9
6	6062	0.1077	1.5	0.3		10.5	9.8
7	4993	0.0887	1.7	0.5		9.0	8.4
8	5578	0.0991	1.7	0.6		9.9	9.4
9	5387	0.0957	1.8	0.7		9.6	9.1
TOTAL	56288	1.0000	16.3	3.7		98.5	92.4