Synergistic Effects of Urban Heat Island and Heat Waves in the Greater Kuala Lumpur Region

Research on the synergy between urban heat islands (UHI) and heat waves (HW) in tropical cities remains scarce, despite the increasing frequency, duration, and severity of HW in Southeast Asia. Studies indicate that UHI intensity (UHII) can increase (positive), decrease (negative), or remain unchanged (neutral) during HW. This study investigates two HW events in 2016 (Case 1) and 2020 (Case 2) to understand the UHI-HW synergy in Greater Kuala Lumpur (GKL). The Advanced Research WRF (ARW) model version 4.2.2, coupled with a single-layer Urban Canopy Model (UCM), was employed to assess UHI impacts during these HW events in GKL, comparing them with periods immediately before and after the events, referred to as Pre-Post HW (PPHW). Results demonstrate that UHII is enhanced during HW in both observations and simulations. The maximum observed UHII values were recorded at noon, reaching 2.3°C at 16:00 LT in Case 1 and 3.7°C at 15:00 LT in Case 2. This corresponds to increased daytime radiation, with the most pronounced variations recorded at 15:00 LT (433.0 W/m²) in Case 1 and at 16:00 LT (243.1 W/m²) in Case 2. The average cumulative sensible heat flux (Q_H) difference was notable, reaching 289.7 W/m² in Case 1 and 135.0 W/m² in Case 2 for urban areas, and 498.5 W/m² in Case 1 and 286.9 W/m² in Case 2 for rural areas. The Bowen ratio consistently increased during the transition from HW to PPHW conditions. Consistently across all measurement methods, the evidence indicates a clear and positive synergy between UHI and HW in GKL. This study provides valuable insights for future urban planning and mitigation strategies, particularly for tropical regions vulnerable to extreme weather events.