The convective-to-total precipitation ratio and the “drizzling” bias
in climate models
Abstract
Overestimation of precipitation frequency and duration while
underestimating intensity, i.e., the “drizzling” bias, has been a
long-standing problem of global climate models. Here we explore this
issue from the perspective of precipitation partitioning. We found that
most models in the Climate Model Intercomparison Project phase 5 (CMIP5)
have high convective-to-total precipitation (PC/PR) ratios in low
latitudes. Convective precipitation has higher frequency and longer
duration but lower intensity than non-convective precipitation in many
models. As a result, the high PC/PR ratio contributes to the
“drizzling” bias over low latitudes. The PC/PR ratio and associated
“drizzling” bias increase as model resolution coarsens from
0.5o to 2.0o, but the resolution’s
effect weakens as the grid spacing increases from 2.0o
to 3.0o. Some of the CMIP6 models show reduced
“drizzling” bias associated with decreased PC/PR ratio. Thus, more
reasonable precipitation partitioning, along with finer model resolution
should alleviate the “drizzling” bias within current climate models.