Time change of water cycle in Huaihe River Basin

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Huaihe River Basin is located where the significant subtropical front, so-called the Meiyu (Baiu) front, stagnates in early summer. Floods and drought occur very often there. HUBEX (Huaihe River Basin Experiment) is one of the sub-project of GAME (GEWEX Asian Monsoon Experiment) and will be carried out from 1996 fiscal year to clarify the water cycle around the basin and its variation toward the establishment of predictability of the floods and the drought there. The present research project was carried out in 1995 fiscal year to clarify and their mechanisms by collaborating between the meteorologists and the hydrologists in Japan and China, as a pilot study of HUBEX.In the HUBEX,we will make intensive field observations in 1998, such as intensive rawinsonde observation for input the regional 4-dimensional data assimilation, three Doppler Radars observation by the Japanese side for producing the Radar-Raingauge Composite Data and for retrieval of thermodynamic fields of meso-beta-scale … More cloud systems, special field observations on interaction processes between land-surface and atmosphere including hydrology, and construction of the coupled meso-scale atmosphere and land-surface model.The present study examined the above mentioned items with use of the data available so far, including the pilot analysis of the case in summer of 1991 when the big flood occurred in the Huaihe River Basin The survey of data and informations was also made with visit of the basin by the Japanese scientists. These results and the future problems were summarized at the HUBEX workshop in Nagoya in March 1996. Main finding are as follows.1) In the flood period in 1991, not only large moisture inflow from the south into the basin persisted, but also effective macro-scale convergence (outflow from the northern boundary was very small) was also remarked. Contribution of local evapotranspiration to the areal precipitation was not so small even in that period.2) Cumulonimbus clusters with remarkable diurnal variation (maximum in the evening) was observed in the several regions adjacent to the Baiu frontal zone in summer of 1979. The role of the surface heating suggested to be rather different among these regions.3) With use of the Doppler Radar observation data together with the conventional ones around the Japan Islands in July 1988, maintenance process of a meso-beta-scale system was clarified by the retrieval of these data. Sensitivity test of the different cumulus parameterization was made for that case.SiBUC (Simple Biosphere Model including Urban Canopy) was contracted and checked by applying for the Biwa Lake basin. The distributed hydrological model, which can predict the river discharge, was also tried to be improved.5) Scheme for evaluating the surface heat and moisture fluxes over land with use of conventional surface meteorological data was contracted. Less