Spongy land-use for regional plans based on hydrological extreme indices, a case of Guangdong-Hong Kong-Macau Greater Bay Area

Regional developments decisions affect coupled human and natural systems to regulate extremes. Changing climate and land uses increases uncertainty of regional runoff extremes because of altering thermal conditions and moisture fluxes. The Guangdong-Hong Kong-Macau Greater Bay Area (GBA) is a new initiative which will lead to a rapid socio-economic and population growth in the region. Thus, sustainable regional planning is needed to address uncertain hydrological conditions. This study proposes “spongy land-uses” for increasing resilience to environmental changes and natural disasters. Through creating spaces like a sponge which absorbs and stores water can alleviate regional drought and flood risks. Using the ERA5 datasets, three hydrological extreme indices are computed to quantify spatial-temporal hydrological patterns in the GBA from 1981 to 2019. The three indices are simple Precipitation Intensity Index (SPII), the Standardized Precipitation Evapotranspiration Index (SPEI), and the Standardized Runoff Index (SRI). Also, regional land-use patterns are defined based on the local climate zone (LCZ) classification derived from satellite images in 2009 and 2019. Results show that the intensified land use with densified buildings and extensive natural areas will reduce hydrological extreme events. Denser vegetation also enables the land to be spongy through regulating and storing the fluxes of precipitation, evaporation, and runoff. However, large-scale water bodies increase temperature and evaporation which are related to increasing the likelihood of regional droughts. Thus, for the GBA to reduce flood and drought risks, regional land-use development plans should consider compact building blocks, dense vegetation groups, and less large-scale blue infrastructure features. Moreover, this analysis provides a new approach for decision-makers and planners on how to achieve “sponge” targets in terms of land-use for water disaster management in emerging city clusters similar to the GBA.