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Hi Emily – This is set two of our detailed slides. We’ve taken a look at average annual temperature for 26 sites in the San Diego county region. We’ve narrowed down to 8 sites and looked at the maximum temperature. Just a quick look here at that plot for San Diego Lindbergh and then on to minimum temperature. We see what seems to be a very slight trend towards cooler maximum temperatures at San Diego Lindbergh. These are annual average values (thus don’t reflect just one particular time of the year like summer). Again we see the variation is small (hovering around 21 degC on the y-axis; the average temperature hovered around 18 degC on the y-axis). The maximum temperature shows the same interesting “jump” in the late 1970s and slighter decline in the early 1980s.
These plots look at the annual average minimum temperature at our 8 select sites. These records all seem reasonable. We can see a definite warming trend at most of these sites. The late (2010ish) drop in tmin at Imperial would be suspect and deserve further investigation. Just a quick closer look at the tmin for Lindbergh next.
The San Diego Lindbergh location shows a solid record (no missing data). Again we have the interesting “jump” in the late 1970s and similar but not as strong decline in the early 1980s. Kristen is investigating this with Alex Tardy (National Weather Service San Diego) and we’ll see if we turn up any information about this. Otherwise it is clear the low temperature at night has been warming from around 12.5 at the beginning of the record (early 1940s) to around 14.5 today (2010s).
Now we can compare what we have just looked at (annual average minimum temperature on the left) with what Kristen provided (minimum temperature every day during the months of May through October). Notice the y-axis covers a broader range. It is interesting to look at the months of May-Oct because we are interested in nighttime warming (especially warmer evening temperatures during heatwaves).
The “bubble” plot below is from Kristen and shows heat wave activity by looking at daytime maximum and nighttime minimum temperatures. For this plot we see the year (as before) on the x-axis. Now the y-axis shows month/day from May 1 (bottom of y-axis) to November 1 (top of y-axis). Kristen defines a 95th percentile value based on the daily (May-Oct) max/min temp for 1950-1999. This would represent a very warm day or evening and the red circles show when such an day occurs. Nighttime heatwaves are shown by the blue circles. Circle size indicates the number of days in sequence we have warm daytime temperatures or when nights are warm (larger circles would then mean longer heatwaves).
The heat wave index (HWI) is plotted here on the y-axis. This index is a sum (from May through Oct) of the number of days the temperature exceeds the 95th percentile. The red plots the tmax sum and the blue plots the tmin sum. Both values are positive from zero.
