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December and January DLI in Everglades City, Florida

I've been reading about the rains and clouds in South Florida and how extraordinary the past couple months have been. I saw these charts from Travis Shaddox, and I wondered what the light would be in photosynthetic units.

I downloaded monthly summary data since March 2007 for Everglades City from the NOAA. I use these data because they include global solar radiation, and I converted from energy units of MJ/m2 to photosynthetic units of mol/m2 using the 2.04 conversion factor of Meek et al.

This shows the average daily light integral (DLI) each month. One can see the seasonal changes, and one can also see that December 2015 had the lowest DLI of any December and that January 2016 had the lowest DLI of any January. I plotted all the data I could get, which is since 2007; I don't know what the values would have been before that. In the past decade, though, these were the lowest.

image from farm2.staticflickr.comLooking just at December and January year by year, January 2016 really stands out for having a low DLI. Blue triangles are December DLIs and red circles are January DLIs; the vertical dashed lines (blue for December, red for January) show the averages prior to Dec 2015 and Jan 2016.

image from farm2.staticflickr.com

In a normal year at Everglades City, January would have more photosynthetic light than December. For seven out of the past eight years, the month of December had a lower DLI than January.  Only 2014 had a lower DLI in January than in December. But January 2016 is a big outlier; not only does January 2016 have the lowest DLI of any of the previous Januaries, but it also has a lower DLI than any of the previous Decembers.

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