*2.3. In-Situ Ground-Based Rainfall Observations*

Hourly rainfall data during the monsoon season from 2014 to 2017 were obtained from a dense network of 138 rain gauge stations from the Thailand Integrated Water Resource Management System, operated by the Hydro-Informatics Institute (HII) in Thailand (Figure 1). Data were quality controlled by mirroring the density distribution functions of neighbouring stations to remove outlier values considered as noise. These observations were then further interpolated using the Ordinary Kriging interpolator from Golden Software [47] at 0.1 degrees for each hour to match the spatial and temporal resolution of the GPM-IMERG data. This method was selected due to the moderated topographic conditions of the study area and density of the rain gauge measurements. Raingauge data were interpolated using an exponential variogram with a sill of 1.14 (mm2/h2), a range of 4.4 km and a nugget of 0.66 (mm2/h2). It must be noted that interpolation methods for rainfall data are subject to uncertainty e.g., [48,49]; however, in our case, a dense and optimal rain gauge distribution can reduce the level of uncertainty from the interpolation method [50].
