| dc.description.abstract | This thesis utilized one-way coupled meteorhydrology simulation system for typhoon’s ensemble forecast to know the relationship between Typhoon’s track and precipitation and investigate what role uncertainty of precipitation does in the watershed river stage simulation. Typhoon Fanapi (2010) landfall Taiwan in September 19th and produced heavy rainfall that resulted flooding disaster in south Taiwan. Therefore, this study discusses the Kao-Pin river basin as hydrological model’s study area where the typhoon
disaster affected.
This study uses WRF mesoscale model with four nested domain to simulated typhoon’s 72-hour track and precipitation forecast. Using variability of the physical parameters, including different cumulus, microphysics and boundary layer physical scheme, establishes the 24 members of the group ensemble. From different ensemble features, we assess the performance of its path forecast with rainfall forecast, and establish two ensemble composition：1) track ensemble：according to different paths tend to summarize the two ensemble groups and 2)physical ensemble：changing a single type physical parameter scheme to set the ensemble groups, using different combinations of ensemble set to discuss its range of uncertainty. Finally, taking each ensemble member’s rainfall forecast into WASH123D hydrological model, as rainfall information input, to simulate the water stage forecast in the Kao-pin river watershed. Therefore, we can assess the weather patterns of precipitation forecast errors
impact on the water stage forecast.
From the result of track ensemble, the group with better track forecast also have better rainfall and water stage forecast result. For the physical group, especially the cumulus ensemble, because of the variability of physical parameter, there are more variability between the track forecast of each ensemble members, so as in the rainfall and stage simulation result. Rainfall errors and hydrological simulation results in the watershed are closely related, so the local region can be found that the rainfall variability of ensemble forecast will be reflected in the variability of simulating water stage. From the correlation analysis, we can find that the typhoon track forecast errors will be significantly reflected in the rainfall forecast errors, and errors in the main rainfall area will be magnified. For the flow stage forecast, the ensembles with larger rainfall forecast error variance have larger stage forecast error range, and the flow stage forecast error range will be have small amplification by the rainfall error range. But for some ensemble group setting, the amplification phenomenon isn’t as obvious as others. It may be due to the lack of ensemble members in ensemble group or
the similar error properties.
| en_US |