Estimation of probable maximum precipitation (PMP) in Hong Kong under future changing climate based on statistical downscaling

Climate change impacts on probable maximum precipitation (PMP), the theoretical greatest rainfall depth for a specific area at the city level, are still unclear. In this study, we evaluate future changes in 24-h PMP in Hong Kong by statistically downscaling the outputs of five CMIP6 Global Climate Models (GCMs) under three Shared Socioeconomic Pathways (SSP) scenarios (i.e., SSP126, SSP370, and SSP585). The downscaling results demonstrate the methods' satisfactory ability to estimate PMP values in the reference period (1986–2014). The projections exhibit increases in annual maximum daily precipitation in the future (2071–2099) with the largest average increment of 28.8% in SSP585. The multi-model ensemble mean shows the increases in the 100-year return period annual maximum daily dew point temperature (Wm) and the dew point temperature of annual maximum daily precipitation (Ws) in the future. Meanwhile, larger changes in Wm relative to Ws lead to a rise in the moisture maximization ratio (Rm). With the combined effects of the changes in precipitation and dew point temperature, the 24-h PMP estimates corresponding to 10 km2 in the SSP126, SSP370, and SSP585 scenarios are expected to increase, reaching 1724.6 mm (30.8% increase), 1435 mm (8.3%), and 1788.1 mm (35.6%), respectively.