Sensitivity of extreme 2022 Pakistan precipitation to physics parametrization options in WRF

Pakistan is one of the most vulnerable countries to climate change due to its large exposure and vulnerability. In particular, climate models project an increase in heavy precipitation and flood intensity or frequency in the area. However, some uncertainties remain, which are in part related to its complex orography interacting with local dynamics, such as the Karakoram high-mountain region and the Indian summer monsoon. As a consequence, convection-permitting high-resolution simulations are needed. These allow for a better representation of steep orography and resolve deep convection, improving the simulation of precipitation. However, physics parametrization options need to be tested at high-resolution in order to improve these models.

This work evaluates the performance of different parametrization schemes in the Weather Research and Forecasting (WRF) model in simulating the extreme precipitation events that occurred in Pakistan in August 2022. This extreme precipitation primarily affected Southern provinces and led to disastrous flooding that resulted in numerous deaths, displaced people and loss of infrastructure and crop production. It was caused by westward propagating cyclones interacting with hot, moist air advected from the Arabian sea.

Results show differences in the spatial distribution and intensity of precipitation. In most setups, cyclones show a northward bias, where they interact with steep orography producing anomalous precipitation. Simulations are most sensitive to the microphysics parametrization, with the Thompson microphysics scheme producing the best results with respect to observations and reanalysis.