That graph looks quite old - here is a more current one showing the continued decline: https://ourworldindata.org/data-insights/japans-cherry-trees-have-been-b

That graph looks quite old - here is a more current one showing the continued decline: https://ourworldindata.org/data-insights/japans-cherry-trees-have-been-blossoming-earlier-due-to-warmer-spring-temperatures https://ourworldindata.org/data-insights/japans-cherry-trees... Looks like the 20 year average is around 2 April.