Comparing Global Warming and Anthropogenic Heat Impacts on Extreme
Precipitation in urbanized Pearl River Delta area based on Dynamical
Downscaling
Abstract
This study compares the impacts of global warming and intense
anthropogenic heat (AH) on extreme hourly precipitation over the Pearl
River Delta (PRD) megacity, located in coastal South China. Using the
cloud-resolving Weather Research and Forecasting (WRF) model coupled
with the single-layer urban canopy model (SLUCM), three downscaling
experiments were carried out: the first (second) having zero
(300W/m2 as diurnal maximum) AH values prescribed over
PRD urban grids, under the same current climate conditions. The third
experiment with AH=300W/m2 under future projected
climate representative concentration pathway (RCP) 8.5. Boundary
conditions were derived from PRD extreme rainfall episodes, identified
from the Geophysical Fluid Dynamics Laboratory Earth System Model
(GFDL-ESM2M) historical and RCP8.5 runs. Global warming forcing leads to
~20 to more than 100% increase in the probability of
hourly precipitation with the magnitude of 20-100mm/hr over urban
locations. The enhancements from intense AH forcing were similar.
However, two types of forcings have distinct signatures in modulating
the thermodynamic environment. Warming due to AH is limited to the
lowest 1km above ground, while global warming warms up the whole
troposphere. Intense AH results in enhanced convective available
potential energy (CAPE) and reduced convective inhibition (CIN) within
the megacity, allowing convection to be triggered more easily and with
more vigor. On the other hand, global warming enhances both CAPE and
CIN, over both urban and rural areas. Our results highlight the
different physical mechanisms of AH and global warming in exacerbating
extreme urban rainfall, despite their having similar impacts on the
rainfall intensity.