Investigating the characteristics and dynamics of rainfall in Singapore using a GPS-derived proxy to precipitable water.

Located in the Maritime Continent, Singapore has a tropical rainforest (Af) climate under the updated Köppen-Geiger classification system. However, the dominance of island archipelagos in the Maritime Continent with extensive coastlines creates a unique regional climatology dominated by diurnal-cycle modulated rainfall that distinguishes it from other tropical rainforest regimes in South America and equatorial Africa. We investigate the characteristics and dynamics of rainfall in Singapore using Zenith Wet Delay (ZWD) that are derived from continuous GPS data as a direct proxy to precipitable water. We find that ZWD shows significant positive correlation with rainfall at hourly scale, daily scale, and monthly scale, with spearman correlation coefficient to be 0.33, 0.4, and 0.7-0.8, respectively. The diurnal-scale correlation in particular shows strong seasonality indicating the importance and interaction of different processes, such as monsoon winds and diurnal land-sea breeze, at work during different times of the year. We also find that ZWD shows a strong response to precipitation events, and this response seems to vary depending on the type of event. Therefore, we believe that there is great potential in using GPS Meteorology to nowcast extreme events over Singapore.