Hong Kong’s changing climate in 7 charts: from quadrupled ‘very hot days’ to record rainfall

Hong Kong is witnessing a dramatic shift in its climate, with the number of "very hot days" in a year nearly quadrupling over the past decade. The Hong Kong Observatory (HKO) data reveals a concerning trend in the city's summers.

From 2000 to 2020, Hong Kong averaged 13.4 "very hot days," defined as days with temperatures reaching 33 degrees or higher. However, since the 2020s, the figure has surged to over 50 very hot days annually, with 54 recorded in 2021 and 2023 alone. As of September 21, there have already been 30 very hot days this year.

The frequency of heat warnings issued by the HKO has also tripled since 2000, climbing from 464 hours to over 1,400 hours in 2021. Heat warnings now account for at least 13 percent of every calendar year, up from just over 5 percent in 2000. The very hot weather warning is triggered by a heat index threshold that considers temperature, humidity, and airflow.

The term "extremely hot days," defined by the HKO as days with temperatures of 35 degrees or higher, was previously unheard of in Hong Kong. Since 2016, the city has averaged 4.6 extremely hot days per year, with three already recorded in August this year.

Summer in Hong Kong is now longer than ever, with very hot days extending beyond the traditional June-to-August timeframe. Over the past decade, these days have started as early as May and persisted into September and October. Between 2021 and 2025, there were double-digit numbers of very hot days in September, a stark contrast to single-digit or zero figures in previous years.

August has also become the hottest month in recent years, with its mean temperature regularly exceeding the "normal" threshold. Since 2016, August temperatures have consistently surpassed the "normal" level of 28.7 degrees, with only two years dipping below this average between 1980 and 2015.