On perception and autumn colours

Richardson Lab members almost unanimously stated that this year was the brightest and most spectacular autumn display of colours in a long time. However, people are notoriously bad at accurately quantifying pretty much anything they see, hear, smell or feel around us. We often perceive the world differently from it’s physical (absolute) reality. This is easily illustrated by various types of optical illustions or the fact that we do not feel absolute temperatures, only change.

Not only does our brain play tricks on our senses, it also fails us when it comes to interpreting long term (environmental) change, as climate change is slow and our cognitive bias leans towards instant action and gratification.

Begs the questions, can we tease apart the intensity of this years autumn colours, and how they compare to previous years using PhenoCam based data using a more quantitative approach? More so, was this autumn really as spectacular as most people in the lab seem to agree upon?

In order to answer these questions we need to look at some PhenoCam data. Normally we look at the greenness signal, which is mostly driven by the presence of healthy green leaves. In this case however, I focused on how red the leaves were during this autumn. In the figure below you see a time series of canopy redness at the Bartlett research forest in the White Mountains, NH. In this graph you see two high peaks which are caused by leaves turning colour, from green to yellow / red, in autumn in 2014 and 2015.

time_series_rcc

The yearly maximum value in this graph tells us how intense the colours were. A metric for the duration of the colour intensity can be calculate as the sum of a set number of values before and after this peak value, where a higher value indicates a longer duration of peak colour. Below I show peak values and the summed values for a week before and after the maximum Rcc value.

When looking at absolute values one can see that 2014 was actually the better (left figure, dashed line), brighter year. However, if considering the duration of peak colour 2015 wins by far (right figure, dashed line). At this location autumn colours were especially intense and long lasting (which increases the odds for leaving lasting impressions on lab members going hiking and leaf peepers in general). So in this case, our senses weren’t fooled – and we have the data to prove it!

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