177 / 2024-09-10 16:41:29

Future Changes in Coastal Warm-Sector Flood-Producing MCS in Southern China

climate change,flood,mesoscale convective system

During the pre-summer rainy season in southern China, MCS associated heavy rainfall frequently occurs in the warm sector hundreds of kilometers to the south of a front or without any front, which is one of the major contributors for coastal flooding events during this period. The intensity and frequency of strong convective storms are expected to rise with warming climate, posing a greater threat of extreme rainfall in the future. This study aims at revealing the future changes of coastal warm-sector MCS in southern China on its related precipitation features and essential mesoscale process associated based on quasi-idealized WRF simulations and pseudo global warming (PGW) approach.

Typical warm-sector heavy rainfall events are selected to produce composite environments that force the quasi-idealized simulation in current climate (CTRL). After that, the climate sensitivity experiment (PGW) is conducted with the same configurations except that it is forced by reanalysis data plus a climate thermodynamic perturbation derived from a 32-model CMIP5 ensemble climate change signal for SSP5-8.5 scenario.

Comparisons between PGW and CTRL reveal that 12-h accumulated area-averaged rainfall increases 51% by the end of 21th century, with the maximum rising from 333.1 mm to 703.4 mm. As for convection population, the frequency of convection weaker (stronger) than 20dBZ increases (decreases). The rainfall distribution and rainfall maximum are characterized by a north shift, which is largely due to stronger southerly LLJ in warming climate. Moreover, the MCS is initiated ~1h earlier in PGW, with more unstable inflow and stronger backbuilding process leading to larger rainfall accumulation. Notably, although dynamic climate change signal is not included in the current experiment, the LLJ is significantly enhanced by increasing latent heating. The LLJ, latent heating, and deep moist convection may therefore link as a positive feedback in warming climate and eventually lead to extreme rainfall.