TRMM and Thailand Daily Gauge Rainfall Comparison

Daily rainfall data collected from more than a hundred gauges over Thailand for the period 1993-2002 have been used to study the climatology, seasonal and non-seasonal rainfall variations for different regions of Thailand. Climatologically, Thailand has a tropical climate, influenced by the monsoon and the movement of the ITCZ. In the northern region, most rainfall occurs during JJA and in SON in the southern region. Comparison of Thailand gauge data with the Global Precipitation Climatology Center (GPCC) monitoring product and version 6 (V6) TRMM satellite and gauge merged analysis (3B43) show small biases of 1.4 mm/month and 0.62 mm/month, respectively. Version 5 (V5) TRMM microwave calibrated IR (3B42) estimates are much higher than the rain gauge measurements with a bias of 27.8 mm/month. The daily gauge data, binned at 1 x 1 degree, is lower than V5 3B42 by 0.88 mm/day with RMSD of 9.71 mm/day. However, the V6 3B42 is much closer to the gauge analysis with a bias of 0.15 mm/day and RMSD of 9.6 mm/day. While there is still a positive bias of V6 3B42, scatter plots show that the satellite product is incapable of capturing some of the extreme rain events. Statistical analyses of rain events show probability of detection (POD), false alarm rate (FAR) and critical success index (CSI) of 0.92, 0.35 and 0.62, respectively for V5 and 0.88, 0.33 and 0.62 for V6. The CSI is best for the rainy season (JJA) with a POD of 0.97 and FAR of 0.29 and worst for the dry season (DJF) with a POD of 0.62 and FAR of 0.58. The biases for all the regions are substantially reduced for V6, except for the East region, which may be attributed to small-scale heavy rainfall at the coast.