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Middle and eastern routes of the South-North Water Diversion Project (SNWDP) of China, which are approximately located within the area 28°-42°N and 110°-122°E, are being constructed. This paper investigates the past climatic variations on various time scales using instrumental and proxy data. It is found that annual mean surface air temperature has increased significantly during the past 50-100 years, and winter and spring temperatures in the northern part of the region have undergone the most significant changes. A much more significant increase occurs for annual mean minimum temperature and extreme low temperature than for annual mean maximum temperature and extreme high temperature. No significant trend in annual precipitation is found for the region as a whole for the last 50 and 100 years, although obvious decadal and spatial variation is detectable. A seesaw pattern of annual and summer precipitation variability between the north and the south of the region is evident. Over the last 100 years, the Haihe River basin has witnessed a significant negative trend of annual precipitation, but no similar trend is detected for the Yangtze and Huaihe River basins. Pan evaporation has significantly decreased since the mid-1960s in the region in spite of the fact that the trend appears to have ended in the early 1990s. The negative trend of pan evaporation is very significant in the plain area between the Yangtze and Yellow Rivers. There was a notable series of dry intervals lasting decades in the north of the region. The northern drought of the past 30 years is not the most severe in view of the past 500 years; however, the southern drought during the period from the 1960s to the 1980s may have been unprecedented. The dryness-wetness index (DWI) shows significant oscillations with periodicities of 9.5 and 20 years in the south and 10.5 and 25 years in the north. Longer periodicities in the DWI series include 160-170- and 70-80-yr oscillations in the north, and 100-150-yr oscillations in the south. The observed climate change could have implications for the construction and management of the SNWDP. The official approval and start of the hydro project was catalyzed by the severe multiyear drought of 1997-2003 in the north, and the operation and management of the project in the future will also be influenced by climate change-in particular by precipitation variability. This paper provides a preliminary discussion of the potential implications of observed climate change for the SNWDP. [ABSTRACT FROM AUTHOR]

Summary: In this paper, the trends of the annual streamflow and precipitation and cross correlations between them were analyzed in nine large river basins of China during 1956–2005. The results indicate that: (1) the annual mean streamflow decreases in arid and semi-arid regions of north China; however, increasing trends occur in south and Southwest China; (2) the annual streamflow and precipitation exhibit reasonable correlation in nine large river basins except those located in inland areas. The annual streamflow over most areas of China is fed by precipitation; however, the decline in streamflow is faster than the decreases of precipitation since 1970s in the arid and semi-arid regions of north China. The relationship between the annual precipitation and streamflow presents a non-stationary state in north China. This non-stationary relationship is strongly influenced by both human activities and precipitation changes; (3) a significant increase of water use might be the major factor responsible for the steeper decline in streamflow than in precipitation in Haihe River, Yellow River and Songliao River basins in north China. In inland river areas, increase of water use and actual evapotranspiration might result in decline in streamflow although precipitation has an increase tendency. This paper sheds light on the non-stationary relationship between annual precipitation and streamflow and possible underlying causes, which will be helpful for a better understanding of the changes of precipitation and streamflow in China at large scale and in other regions of the world. [Copyright &y& Elsevier]

Abstract: Long-term changes to the Yellow River delta in China have received considerable attention not only because of the growing economic importance of the delta region but also because they provide a clear example of the dominant role played by anthropogenic effects upon a large dynamic river delta. This paper presents a detailed study on the morphological consequences of reduction in river sediment load and influence of human activities based on sediment load data at three gauging stations in the upper, middle and lower reaches of the Yellow River basin from 1950 to 2007. The results indicate that sediment loads at all three gauging stations display a gradually decreasing trend over the past 58years. The primary reason for this decrease is shown to be due to various human activities, including the construction of Longyangxia and Liujiaxia reservoirs in the upper reaches, water–soil conservation practices and the commissioning of Sanmenxia and Xiaolangdi reservoirs in the middle reaches. It is estimated that water–soil conservation practices which are a major factor to the decrease of sediment load at Huayuankou gauging station account for 40% of the total amount of reduction, sediment trapping by Sanmenxia and Xiaolangdi reservoirs account for 30% of the total amount of reduction and the 10% decrease is caused by human activities in the upper reaches. The remaining 20% decrease is attributed to precipitation decrease. The reduction of sediment load has directly impacted on the lower Yellow River and the delta region, causing alternate changes between siltation and scouring in the lower river channel along with an increased rate of erosion over the whole Yellow River delta. [Copyright &y& Elsevier]

Hourly summer precipitation data recorded at 21 stations during 1961-2004 in the Haihe River Basin in North China were analyzed. The results show that the precipitation frequency and amount and the morning peak mainly relating to long-duration rainfall events decreased during this period, whereas the normalized afternoon peak mainly relating to short-duration events increased, which may suggest that the proportion of short-duration rainfall has increased as the total summer rainfall has decreased. For short-duration events, the mean intensity and peak intensity increased at most stations and the time to peak intensity decreased, which may be attributable to the higher thermal contrast between the warmer lower surface and cooler upper level. In the case of long-duration events, the total amount was significantly correlated with the East Asian summer monsoon index for the period 1961-2001 (correlation coefficient of 0.63). Although the total amount of rainfall in long-duration events decreased in the basin, the mean intensity and peak intensity, as well as the extreme hourly precipitation, increased in the western basin and decreased in the eastern basin. [ABSTRACT FROM AUTHOR]