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 Global warming is associated with substantial increases in heatwave frequency, duration, and amplitude over Southeast Asia. The increase of heatwave amplitude with global mean temperature is quasilinear, and that of heatwave frequency and duration are nonlinear. A warmer future will see a higher risk ratio with rarer extreme heatwave events relative to the current climate.

Based on updated quality controlled daily records, extreme events were defined using temperature indices proposed by the Commission for Climatology/Climate Variability and Predictability project's Expert Team on Climate Change Detection, Monitoring and Indices, and temporal trends during the 1970-2009 period were examined in Thailand. Results revealed that Thailand has indeed experienced significant country-wide warming over the last four decades, and extreme events associated with both the cold and warm extremes of daily minimum and maximum temperature distributions have changed accordingly. Trends in temperature indices showed much spatial trend coherence and widespread significant warming, generally consistent with the regional evidence recently documented in other Asia-Pacific Network countries. Significant upward trends in temperature extreme indices were found in the annual number of warm nights and days, the annual occurrence of warm spells, tropical nights, summer days, and the highest and lowest values of daily minimum temperatures. In contrast, significant downward trends were observed in the annual number of cold nights and days, the annual occurrence of cold spells, diurnal temperature range and annual extreme temperature range. Changes in these temperature extreme indices were consistent with a significant shift in the temperature distribution toward warmer conditions over the recent decades. To address changes in Thailand's temperature more clearly, however, the plausible underlying mechanisms, including urbanization effects, need to be further studied.

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