Wednesday, April 8, 2015

Cherry Blossoms as Indicators of Climate Change

Posted by Richard Primack

The flowering of cherry trees is one of the most beautiful sights in the spring. Cherry trees are also extremely sensitive to temperature, flowering earlier in warm years and later in cold years. The Japanese people greatly enjoy their annual cherry blossom festival, taking time off from work, walking under the trees, and meeting friends for outdoor parties.  In Tokyo, a warming climate has caused the blooming of the cherry trees to gradually change over the last century from mid-April to late March.

Figure 1. People enjoying the cherry blossom festival in Japan

The oldest records of cherry blossom flowering come from Kyoto where the festival has been celebrated for over 1200 years. There have been long periods of earlier flowering and later flowering associated with global changes in temperature. Starting about 150 years ago, the cherry trees have been flowering ever earlier due to a combination of urbanization in Kyoto (more buildings, more pavement and streets, and fewer trees) and warming temperatures. Over recent decades, cherry trees in Kyoto have been flowering earlier than they ever have in the past.

Figure 2. Cherry blossoms in Japan are getting earlier over time, and have been particularly early in recent years

The effect of urbanization on cherry trees is illustrated by the city of Osaka. Using 80 observation points around the city, researchers show that trees flower earliest in the center of the city where it is warmest due to urbanization. 

Figure 3. This map of Osaka shows that trees flower earliest in the center of the city

To read more about cherry blossoms as indicators of climate change, see our articles in Biological Conservation and Arnoldia.

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