Spatial and temporal changes of precipitable water vapour in Thailand

The study examines spatial and temporal changes in monthly precipitable water vapour (PWV) over Thailand using 37 years of monthly ERA-Interim re-analysis data (1981-2017). PWV from ERA-Interim data was compared with that derived from radiosonde observations at four stations and it was shown to have an average root-mean-square error and mean bias error of 0.264 cm and -0.137 cm, respectively. Then, PWV from ERA data was used to estimate spatial patterns of monthly average PWV for the winter (Nov, Dec, Jan), summer (Feb, Mar, Apr, May) and rainy (Jun, Jul, Aug, Sep, Oct) seasons as well as the yearly averages. Statistically significant increases in PWV are found in the rainy season which has been related to the West Pacific index (WP). A second statistically significant increasing trend is found over the southern half of Thailand during the winter season which could be influenced by changes related to the Siberian High pressure.