The summer solstice, Xiazhi, is one of the twenty four solar terms that divide the Chinese solar year and falls in the sixth lunar month, marking the longest day of the year in the northern hemisphere and, within the five phase framework, the point at which yang energy is understood to peak before yin begins its own slow rise through the second half of the year.
Earlier in the season, the Duanwu festival, widely known outside China as the Dragon Boat Festival, falls on the fifth day of the fifth lunar month and is traditionally associated with dragon boat races, the eating of zongzi, glutinous rice wrapped in bamboo or reed leaves, and, in its most widely told origin story, with the death of the poet and statesman Qu Yuan, who is said to have drowned himself in protest at political corruption, with local boats supposedly racing out to try to save him and the rice offerings meant to keep river creatures from his body. The festival's timing near the summer solstice also carries older associations with protective and purifying customs against the heat, humidity, and associated illness risk of the coming height of summer, layering a seasonal health concern beneath the historical commemoration that later became the festival's dominant public story.
Sources The Twenty-Four Solar Terms, knowledge in China of time and practices developed through observation of the sun's annual motion, UNESCO Representative List of the Intangible Cultural Heritage of HumanityUNESCO Intergovernmental Committee for the Safeguarding of the Intangible Cultural Heritage with The Songs of the South: An Anthology of Ancient Chinese Poems by Qu Yuan and Other PoetsQu Yuan and other poets, translated and edited by David Hawkes