Urbanization-induced changes in extreme climate indices in Thailand during 1970–2019

Abstract

Applying the homogenized daily data during 1970–2019, this study examined the urbanization effects on changes in a set of extreme climate indices for large cities across Thailand, where has undergone rapid urbanization in recent decades. Analysis revealed positive urbanization effects on a number of the indices related to hot extremes, providing a consistent picture with the previous studies. Larger and more significant urbanization effects were evident for minimum temperature-related extreme indices, probably resulting from stronger nighttime enhancement of the urban heat island (UHI) intensity. From a sub-regional perspective, the urbanization effects for four clusters contributed, on an average, to half of the total trends of temperature extremes. Another noteworthy finding was marked by significant urbanization-induced increases in the amount, frequency, intensity, and magnitude of rainfall extremes at the urban stations in the Bangkok metropolis and the central part of the country. Analysis showed that most of the rainfall indices in this region exhibited a 100% urbanization contribution. These results highlighted that the Bangkok metropolis and its adjacent urban areas experienced substantial increases in climate extremes, resulting in greater risks from their associated disasters. The mechanisms how urbanization has induced changes in climate extremes in Thailand seem to be complex, depending on many factors including increases in UHI intensity, heat absorption in urban boundary layer, urban-rural roughness, anthropogenic aerosol, and pollutant emissions. However, to better understand their underlying physical processes and mechanisms, climate model-based dynamical experiments and additional analysis of high-resolution satellite data are further needed.