GO OZAWA - CTI Engineering Co,Ltd, Japan
HIRONORI INOMATA - National Institute for Land and Infrastructure Management, Ministry of Land, Infrastructure, Transport and Tourism
KAZUHIKO FUKAMI - International Centre for Water Hazard and Risk Management (ICHARM) under the auspices of UNESCO, Japan

Accurate rainfall data are most basic and important information for accurate inflow forecasting of dam and flood forecasting. However, it is difficult to understand rainfall distribution in ungauged basins in real-time. On the other hand, near-real-time satellite-based rainfall data such as GSMaP_NRT (provided by JAXA, hereafter GSMaP) are widely available for public use, and research has been in progress to apply this type of data to a broad range of areas including flood management in ungauged basins. However, the previous researches have found that satellite-basedrainfall products in general tend to underestimate observed ground rainfall especially for heavy rainfall, which poses a problem in their use for dam inflow and flood forecasting and warning. Thus, a correction method for satellite-based rainfall data to improve the accuracy is necessary to utilize them in practical operations. In some ungauged basins, a few real-time rain-gauge stations have been installed recently. In these basins, merging method for satellite-based rainfall and rain-gauge data can be applied such as Inverse Distance Weighted interpolation (IDW), Co-kriging. Thesemerging methods are expected to improve the accuracy of satellite-based rainfall with rain-gauge data. This paper revealed the relation between the density of rain-gauges and the accuracy of merged GSMaP. The result implies that a certain level of the density (1 station/5,000km2) of rain-gauge stations is necessary for improvement of merged GSMaP

GSMaP, Merging, IDW, ungauged basin, Morakot