Maple Leaves Turn Red 2 Weeks Later Than They Did 50 Years Ago

2003.12.08 Mon

The Japan Meteorological Agency, which makes seasonal observations of biota, has reported that the date by which Japanese maple trees (Acer palmatum) turn color has been delayed by two weeks from 1953 to 2000, and that this trend has been particularly clear since the late 1970s. The agency makes annual observations at its meteorological observatories and weather stations across the country in order to keep track of seasonal changes in plant and animal behavior. This data can be used as indicators of climate and environmental changes.

The arrival of autumn at each site is determined by the date on which roughly 80 percent of leaves of sample maple trees have turned red. The attached line graph shows year-to-year variations on the arrival of the autumn maple leaf season in Japan. The figures in the graph were calculated using data collected from 44 sites from which adequate data were available, and show the average differences between the autumn arrival date for each year and the average year, using data for the 30 years between 1971 and 2000.

Until the mid 1970s, most points on the graph are below zero, meaning that maple leaves tended to turn red earlier than average. In contrast, after the late 1970s, with few exceptions, the advent of autumn leaf season became later than the average year, and since the late 1980s the season has come almost five to ten days later than the average year.

Meanwhile, Japan's annual average temperature has risen by approximately one degree Celsius during the 100 years between 1901 and 2000. In Metropolitan Tokyo, the average temperature for the 1960s was 0.5 degrees C below temperatures for an average year, 0.3 degrees C below average for the 1970s, and 0.1 degrees C below for the 1980s, but 0.5 degrees C above the average for the 1990s, showing a remarkable rise in that decade. Because the arrival date of the autumn leaf season is determined by temperatures in the early autumn of the same year, the delay in the autumn leaf season can be attributed partly to global warming.

Posted: 2003/12/08 10:35:32 PM
Japanese version