"There is probably a connection with global warming," he said.
Typhoons seem to be getting stronger and making landfall more often, he noted, while summer rains are less frequent but heavier.
There are reports that other plants such as azaleas and the Japanese ume plum trees are also blooming off season.
And Wada has heard that Tokyo parks are battling with weeds previously only found in hotter parts of Japan and overseas.
In 2005 the Japan Meteorological Agency issued a report about how rising temperatures are affecting Japanese plants and animals.
The agency found that spring cherry trees are now flowering on average about four days earlier than they did 54 years ago, when record keeping began.
The report also found that Japanese maple leaves are now changing colors 15 days later.
But Hiroyuki Uehara, chief of the applied weather information section at the Japan Meteorological Agency, is still cautious about a link between these trends and climate change.
"I think that one possible reason may be global warming, although it is not clear how temperature variations actually affect such phenomena," he said.
"All we can do is provide long-term observation data."
Meanwhile, the Japanese people are particularly sensitive to any threat to this cultural icon, Wada said.
In addition to the widespread Somei Yoshino, about 350 varieties of ornamental cherry tree grow in Japan.
The tiny flowers symbolize the fragile transience of life and are featured in everything from J-pop music to pottery to kabuki theater. Viewing parties across the country celebrate their blossoms each spring.
And a famous festival in Washington, D.C., honors Japanese culture around the time that the city's cherry trees—a gift from the people of Tokyo in 1912—come into bloom.
(See photos of the cherry blossoms in Washington, D.C.)
Traditionally, Japan's earliest blossoms appear between January and February on the southern island of Okinawa (see a map of Japan). Tokyo's trees usually open up in late March.
"When I was a student in Tokyo in the early 1980s, sakura bloomed around the first of April," Wada recalled. "Now it is closer to March 20."
He pointed out that the cherry blossom season traditionally coincides with the start of Japan's school and business year, making the flowers a symbol of a fresh new start.
"Sakura was linked to that turning point in people's lives," Wada said. "If the time of the [cherry blossom] season changes, so will Japanese sensibility."
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