New Chart: Daily Light Integral (DLI) and Growth Potential (GP)

To show the relative amount of photosynthetically active radiation (PAR) during the times of the year when the temperatures are close to an optimum for warm-season grass growth, I have made this new chart based on a series of calculations that give an estimate of the daily light integral (DLI).

estimated DLI and GP for a selection of world cities

First, for the cities shown, I estimated the mean daily temperature for each day of the year, based on the mean monthly temperatures. Then, using the monthly mean sunshine hours, I estimated the DLI for each day of the year, based on the Ångström equation. The GP for each day was calculated using the growth potential equation of PACE Turf for C4 grasses.

Across a range of temperature regimes, the cities in Asia where C4 grasses are the primary species used, tend to have a lower DLI during times when temperatures are at an optimum for these grasses to grow, compared to cities with similar temperatures in North America.

The contrast on this chart between the cities of Honolulu and Hilo is quite striking, and one finds a clear difference in turfgrass species growing at those two cities, which are quite disparate in DLI, even though they are quite close geographically. In a similar way, careful study of the grass performance in cities with a mean DLI > 40 mol m-2 d-1 compared to those with mean DLI < 40 mol m-2 d-1 suggests that species selection (and maintenance guidelines) for managed turfgrass sites should take into account the DLI, not only the temperature.

On Data, Charts, and Software

Data shown on these charts are from the World Meteorological Organization and, in the case of the Japan motion chart, from the Japanese Meteorological Agency.

The static charts were made using the ggplot2 package in R. Motion charts were made using the googleVis package in R. This document explains the procedure I used to make a motion chart with data from 52 world cities.

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