Jiawei Bao - Understanding extreme precipitation and its links with convective organisation

Event type: 
Seminar
Date: 
6 March 2019
Time: 
2.00 - 3.00pm
Location: 

Climate Change Research Centre, Seminar Room, Mathews Building 4th floor, UNSW, Sydney

Presenter: 
Jiawei Bao
Climate Change Research Centre, UNSW, Sydney
Host: 
Climate Change Research Centre

The response of extreme precipitation to climate change is elusive and evidently does not simply follow Clausius-Clapeyron (CC) scaling. Understanding extreme precipitation is challenging: for example, observational studies have shown opposite signs of change with local warming in different regions. The question is further complicated by the highly variable nature of extreme precipitation, such that events at different timescales may behave differently. This thesis combines observations and a variety of model results to understand how extreme precipitation changes in response to warming and endeavours to explain why the responses can deviate from CC scaling.

First, this work resolves important inconsistencies in tropical extreme precipitation scaling among observational studies, finding that extreme daily precipitation in the warmest tropics is unlikely to decrease with warming as previously derived from a binning method, due to flawed assumptions in the method. Instead, regional-downscaling simulations project that extreme daily precipitation tends to increase almost everywhere in Australia, likely exceeding CC scaling for the strongest events.

This work also identifies convective organisation as important for extreme precipitation scaling, in a suite of idealised simulations. Extreme daily precipitation at a point location is found to increase faster than CC scaling if and when convection becomes more organised with warming. This is because convection is constrained in a relatively fixed region once it becomes organised, which increases daily accumulated precipitation at the rainiest locations. However, convective organisation has a negligible impact on extreme instantaneous precipitation, because of the balance between a negative dynamical contribution (weakened updraft with organisation) and a positive microphysical contribution (increase in precipitation efficiency), both of which are induced by the process of organisation. The results reveal a fundamental discrepancy between short-duration and long-duration local extreme precipitation: instantaneous extremes are more sensitive to microphysical impacts while daily extremes are more affected by dynamical changes.

 

Brief Biography: Jiawei started his PhD in September 2015. His research focuses on the extreme precipitation change with temperature in Australia, with a particular focus on identifying the reasons which lead to the different scaling rates among different regions in Australia by applying statistical methods in observational data and doing some simulations with regional climate models. Jiawei graduated from Beijing Normal University with a master of science degree in 2015. During his masters, Jiawei did some work on model evaluations and simulating the precipitation change in China with WRF.