CHARACTERISTICS AND CAUSE ANALYSIS OF WESTERN PACIFIC SUBTROPICAL HIGH DURING THE HUAIHE RIVER FLOODS IN 2003

1 INTRODUCTION In summer, different assembly of the intensity, location and vertical structure of the subtropical high and the earlier/later time of its seasonal northwards jump bring about different precipitation patterns over China. Therefore, subtropical high activity and its cause during the occurrence of extreme climatic event over China and the cause of China drought/flood are studied to improve weather forecasting.

THE STATUS QUO & TAMING OF THE HUAIHE RIVER

From the angle of regional development, this article gives a brief account of the natural conditions, socio-economic development, the calamitous environment of the Huaihe River, the achievements and existing issues in the harnessing of the River since the founding of the People’s Republic. In addition, it suggests some harnessing tasks set for the on-going Ninth Five-year Plan and some problems to be dealt with prudently.

Interdecadal change of the connection between winter North Pacific Oscillation and summer precipitation in the Huaihe River valley

The relationship between the winter North Pacific Oscillation (NPO) and the following summer precipitation in the Huaihe River valley before and after the mid-1970s is investigated by using the Chinese 160-station precipitation data and NCEP/NCAR reanalysis data from 1951 to 2008.It is found that their linkage appears to have an apparent interdecadal variation.Before the mid-1970s, there was a prominent out-of-phase relationship between the winter NPO and the summer precipitation in the Huaihe River valley.However, such a relationship is significantly weakened afterwards.The change of atmospheric circulations related to the winter NPO before and after the mid-1970s is further addressed.Before the mid-1970s, a strong (weak) winter NPO was followed by the summer situations with anomalous low-level cyclonic (anticyclonic) circulation over the western Pacific and descending (ascending) over the Huaihe River valley.Meanwhile, the water vapor transporting to the Huaihe River valley was reduced (enhanced).These conditions are unfavorable (favorable) for the precipitation occurring in the Huaihe River valley, and thus the local precipitation was decreased (increased).After the mid-1970s, however, the impact of winter NPO on the summer atmospheric circulation system associated with the rainfall in the Huaihe River valley becomes diluted, thereby weakening its linkage to the summer precipitation in the Huaihe River valley.

Dust source of the Holocene loess-soil and pedogenic environmental changes in the upper Huaihe River

Based on field surveys,soil samples were collected at the YPC site,Yuzhou City,Henan Province for analysis of contents of major and trace elements and their variations with XRF and comparison with the curves of magnetic susceptibility,pH value distribution,loss on ignition and particle-size distribution.It was concluded that the dust source of loess in the upper reaches of the Huaihe River Basin was different from that in the Loess Plateau.And the Holocene pedogenic environmental changes in the upper reaches of the Huaihe River Basin were revealed.

Ecological Water Requirement Estimates for Typical Areas in the Huaihe Basin

Aquatic ecosystems require ecological water allocation to prevent from being damaged by natural disasters and undue exploitation. This paper discusses and estimates the ecological water requirements （EWRs） of typical areas in the Huaihe Basin to determine rational allocations of water resources and pro- mote regional improvements of the ecological environment. The main river course, including Hongze Lake and Nansi Lake, was selected as the study subject. Calculational methods for the river and lake EWRs were based on the reasonableness of the results and data availability. The monthly guarantee rate method was used to calculate monthly, flood period, non-flood period, and annual EWRs for the main river course and the main tributaries at two different guarantee rates. The minimum water level method was used to calculate annual EWRs for Hongze Lake and the upper and lower Nansi Lake of 1.521×10^9 m^3, 0.637×10^9 m^3, and 0.306×10^9 m^3. The results were used to evaluate the rationality of the quantity of water resources allocated to ecological uses in the Huaihe Basin during 1998-2003. The result shows that the present water resource allocations in the Huaihe Basin cannot satisfy the basic ecological requirements for some years, especially years with less precipitation.

Holocene loess and its deposition dynamics in the upper reaches of the Huaihe River

The dust source and transporting system are two indispensable aspects in the process of Ioess-palaeosol accumulation. It has been proved that the dust of the Loess Plateau mainly comes from the northwestern inland gobi and desert, transported by the East Asia monsoon systems and westerlies. However, there are little researches with respect to the dust source and deposition dynamics of the upper reaches of the Huaihe River. In the present study, we investigated and collected the YPC section with high resolution in the upper reaches of the Huaihe River. The chronological frame was reconstructed by optically stimulated luminescence （QSL） dating and correlated with the published loess time series. By comparison of the magnetic susceptibility （MS） and grain size （GS） of loess-soil profile among YPC profile, XJN profile （western Loess Plateau） and the JYC profile （southern Loess Plateau）, we find similar climate change and pedogenic process between the upper reaches of the Huaihe River and the Loess Plateau, both experienced an extreme dry and the weakest pedogenesis during the last glacial, followed by a transitional episodes from the cold-dry last glacial to the warm-humid mid-Holocene and increased pedogenesis in the early Holocene, then a most humid-warm and strong pedogenesis in the mid-Holocene, and climate deterioration and decreased pedogenesis occurred during the late Holocene. But the MS of loess-soil profile sequences in the upper reaches of the Huaihe River was much lower than those in the Loess Plateau, and the GS was much coarser than those in the Loess Plateau. Comparison of GS for these three profiles revealed that there were different dust sources, which belonged to different aeolian transporting systems. The loess in the upper reaches of the Huaihe River was a wind blown deposition of near source, while the coarser dust mainly came from loose alluvial deposits of alluvial and proluvial fans of the Yellow River. The yield- ing and carrying dynamics of the dust in the Huaihe River is the northeast wind prevails in the winter half year.

Evaluation and Analysis of RegCM3 Simulated Summer Rainfall over the Huaihe River Basin of China

This study evaluates the ability of the Abdus Salam International Center for Theoretical Physics （ICTP） version 3 Regional Climate Model （RegCM3） in simulating the summer rainfall amount and distribution and large-scale circulation over the Huaihe River basin of China. We conducted the simulation for the period of 1982-2001 and the wet year of 2003 to test the ensemble simulation capacity of RegCM3. First, by comparing the simulated rainfall amount and distribution against the observations, it is found that RegCM3 can reproduce the rainfall pattern and its annual variations. In addition, the simulated spatial patterns of 850-hPa wind and specific humidity fields are close to the observations, although the wind speed and humidity values are larger. Finally, the ensemble simulation of RegCM3 for summer 2003 failed to capture the spatial distribution and underestimated the magnitude of the precipitation anomalies, and the reasons are analyzed.

A comparative study of the atmospheric circulations associated with rainy-season floods between the Yangtze and Huaihe River Basins

Here we present the results from the composite analyses of the atmospheric circulations and physical quantity fields associated with rainy-season for the selected floods cases over the Yangtze and Huaihe River basins for the 21 years(1990–2010),using the daily rain gauge measurements taken in the 756 stations throughout China and the NCEP/reanalysis data for the rainyseasons(June–July)from 1990 to 2010.The major differences in the atmospheric circulations and physical quantity fields between the Yangtze and Huaihe River basins are as follows:for flooding years of the Yangtze River Basin,the South Asia high center is located further east than normal,the blocking high over the Urals and the Sea of Okhotsk maintains,and the Meiyu front is situated near 30°N whereas for flooding years of the Huaihe River Basin,the South Asia high center is further west than normal,the atmospheric circulations over the mid and high latitudes in the Northern Hemisphere are of meridional distribution,and the Meiyu front is situated near 33°N.In addition,there are distinct differences in water vapor sources and associated transports between the Yangtze and Huaihe River basins.The water vapor is transported by southwesterly flows from the Bay of Bengal and monsoon flows over the South China Sea for flooding years of the Yangtze River Basin whereas by southeast monsoons from the eastern and southern seas off China and monsoon flows over the South China Sea for flooding years of the Huaihe River Basin.