Relationship between temperature increase and precipitation extremes in Peninsular Malaysia based on regional climate models / Saiful Anuar Baharudin

Study on the change of precipitations under changing climate is of interest because of their large impact on society. Clausius-Clapeyron (CC) relationship, which governs how moisture behaves with temperature, expected extreme precipitation to intensify by 7% per degree of warming. Research in climatology usually involves two methods: using climate models and statistical properties of historical observations. Although historical observations are often used in guiding the stakeholders in their decisions, climate models are usually used to provide future projections of climate. The coarse resolution of General Circulation Model (GCM) is insufficient in showing how extreme precipitation will affect local climate and thus lead to a scaled down Regional Climate Model (RCM). However, RCM tends to underestimate extreme rainfall when compared with historical observations. This research explores the metrics used to assess climate models and apply them on three RCM available for Peninsular Malaysia. The research starts by first establishing the relationship between observed extreme precipitation with temperature, where decreasing trend was observed in Peninsular Malaysia regardless of location or time investigated, in contrast with CC relationship expectation. The observed trend at 99th percentile of daily rainfall intensity is found to be decreasing as much as −35% per degree of warming. Next, the ability of EC-EARTH (R1), CM5A LR (R2) and ESM-MR (R3) GCM, scaled down under RegCM4-3, in simulating historical observations were assessed where R2 was found to performs the best among the RCM assessed. Hence, R2 was chosen to investigate future changes of extreme rainfall − focused at the 2060-2084 period under RCP8.5 scenario − from the present day climate. R2 projected no significant change in the future monthly cycle or seasonality of extreme rainfall with historical simulations. Further, the mean annual maximum of daily rainfall is also projected to increase across many areas in Peninsular Malaysia, with some coastal area of Pahang, Perak and Kedah will experience an increase of over 70% of the present-day mean, while the coastal area around Kelantan will experience a decrease between 10 to 30% of the present-day mean. However, a small area, especially in the inland area of Peninsular Malaysia, is expected to show no significant changes to the mean annual maximum in the 2060-2084 period from the present-day value. Last, the response of extreme precipitation with temperature is expected to change in the future, thus render historical scaling invalid for future climate. The findings may benefit climatology where CC relationship can improve the performance of climate models to simulate Earth climate, especially to make better predictions of future climate.