Heatwaves vs Observable Data – Big boost with that?

John Entwistle

A few months ago, one of the people commented on this WUWT article: https://wattsupwiththat.com/2021/07/12/the-truth-about-heat-waves/ posted a comment on the effect that heatwave numbers are on the rise, and cites this article on the EPA’s website: https://www.epa.gov/climate-indicators/climate-change-indicators-heat-waves . Embedded in the EPA paper is this diagram:

I am very disappointed that the paper does not provide data, methodology or calculations. It also uses some terms like “local threshold” and “heatwave season” without defining them. This comment prompted me to redirect my inner Willis to see if I could repeat this chart.

What is heat wave?

I start with the definition of a heat wave. I have found some interesting vague definitions on the internet. From Mirriam Webster we have: “Unusually hot weather“; Wikipedia defines it as: “ONE heat wave is a period of unusually hot weather for a long time.“; while the word NOAA has: “A heat wave is simply a period of unusually hot weather that usually lasts two days or more. The temperature must be outside the historical average for a given area.“These definitions leave a lot of room for interpretation. Who has the right to decide what is unusual? Historical average over what time period? Full period average or moving average? What is a local threshold and who determines its value? How far beyond the historical average?

Get some data

I started looking for data by looking for some actual temperature records from my area. I want the data to be observed daily, not monthly summaries or grid estimates. I live in central New Jersey, just outside of New York, and I was surprised to find that, despite the fact that there were private colleges/universities and military bases from all branches of Branch within my house since the revolution, no local organization has recorded, or at least published, a historical daily temperature record. The best that Online Climate Data (https://www.ncdc.noaa.gove/cdo-web/ can provide are three discontinuous datasets from different locations, the oldest one starting… in 1960! On WUWT, it is often said that “climate is 30 years.” If I search for heatwaves from the 60s that means I need to find data from at least 1930 to look for heatwaves from the 60s.

I scoured the internet and found several sources of daily temperature observations in New York starting in the late 1800s:

High Plains Regional Climate Center: High Plains Regional Climate Center – CLIMOD (unl.edu) at the University of Nebraska Lincoln. This site has a good dataset for New York’s Central Park.

Cornell University: weather.nysaes.cals.cornell.edu/history/ whose records were made on their test farm outside of Geneva, NY.

I used Python scripts to collect or parse these datasets into CSV files. There was some missing data, especially in the early years, so records from before 1900 were removed. The Cornell website apparently stopped posting halfway through 2020, so I dropped six the last month of that dataset to match the end of 2019. There were still a few holes left, so I filled in the gaps by calculating the mean of the ten days before each gap and plugging the holes. with that average.

Back to the “normal temperature” question. How to determine the usual temperature for any day of the year? It bothers me that we always think of normal/normal/average temperatures in terms of calendar months. The monthly calendar is a convenient fiction invented, in our case, by the Romans. The months have little or nothing to do with actual climate-related phenomena.

Instead of using the average of the days of the month or the n days before a date, I think it makes more sense to look at the temperatures for each individual day and location over the ~120 time periods of each dataset Whether. This approach gives us an average temperature for each day of the year that we can then use as the basis for our “two-plus days” assessment. Using Python, Pandas, and Matplotlib, I was able to quickly generate a data series for each day of the year for ~120 years of each temperature record, calculating the mean, standard deviation, and squared trendline minimum for each day and plot this to see how the temperature has changed year-over-year for that day.

120 years daily temperature

Every year, citizens across America gather on July 4, American Independence Day, to eat hot dogs, drink beer, and complain about how hot it is. The graph of the US Independence Day temperatures in Central Park from 1900 to 2020 looks like this:

The mean in this graph is the average high temperature value for this day of the year, in this case day 185.

Cornell University has an experimental farm not too far from Geneva, NY, located between Rochester and Syracuse. They have been collecting temperature data since 1891, although they stopped updating their website in mid-2020. If we look at the 4th of July in Geneva from 1900 to 2019, we will see a slightly different picture from the one in Central Park:

Interestingly, the minimum temperature in both locations has increased over the past 120 years.

I thought it would be interesting to see how similar daily charts over a number of days might actually be related to climate – solstice and equinox. Here again is Central Park:

The four summer solstices / equinoxes are the same in Geneva, NY:

Heat wave

To find heat waves, we need to find two consecutive days above normal. I decided to use one standard deviation above the mean temperature for that day of the year as “normal” for that day. I’ll be doing this all year long, not an arbitrary “hot season”. After all, if it’s really warm in the middle of winter, isn’t that a heatwave?

To start with, I defined each day above this threshold value. Here are the number of ‘hot days’ per year in Central Park:

The plot of hot days in Geneva, NY looks like this:

From here, counting the number of consecutive hot days to find heat waves is a simple matter:

Now let’s look at intensity and duration. I will choose intensity to mean the average temperature of all heat waves that year.

These are interesting pictures. Does that mean heatwaves are getting cooler, or has the share of heatwaves in cooler months increased in the second half of the data cycle?

Finally, we can plot the average length of annual heatwaves over the same period:

Decade Summary – EPA . Chart

Averaging the heatwave figures above for each decade from 1900 – 2019 gives us charts similar to those provided by the EPA:

Interestingly, the number of heatwaves per decade in both Central Park and upstate New York between 1960 – 2019 shows an increase in the number of heatwaves per decade, similar to the graph below. EPA, although it looks like they used a higher threshold because the number of heatwaves they cited was much lower. However, the period from 1960 to 2020 doesn’t seem to tell the whole story, as we can see that there was a warmer period in both data sets in the 30s and 40s. The magnitudes and durations I’ve created are quite different from the EPA’s chart for each location.

One chart to rule them all

The EPA just has a set of graphs representing an unspecified area, I assume the entire Earth? I have two sets of charts, one for the city and one for the suburbs. Combining the two by averaging the decimal values ​​for each place gives the following graphs:

I’m not sure what these combo charts tell us. Averaging the number of heatwaves across the two locations appears to mask a steady increase in the number of heatwaves in Central Park. The intensity and duration graphs we created here are not the same as those produced by the EPA. It would be nice to know what data they used to create their charts.

What is clear is that a distance of about 300 miles and an altitude difference of 780 feet produced very different temperature data in these two locations. The heatwave graphs seem to suggest that even thirty years is not long enough to understand the climate in both locations. It would be nice to have hundreds more years of data to see if that seemingly periodic pattern of heat wave numbers is real.

All data and calculations can be found here: https://github.com/jentwistle3/Heatwave_public

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