| In the recent years, the World Climate Reseach Plan (WCRP), International Hydrology Plan (IHP), International Global Biosphere Plan (IGBP) and Global Energy and Water-cycle Experiment Plan (GEWEX) has been working on hydrology-atmosphere coupling research and daily and quarterly forecast of seamless weather, climate, hydrology and water resource.The hydrology forecast includes many aspects such as precipitation, droughts and floods tendency, soil humidity, runoff and soil humidity, runoff and evapotranspiration. The focal point is the hydrological change in the big river basin, based on which, it will estimate the affects to water resource of the region and basin. The estimation mainly involves the influential research of the regional and basin hydrology, water resource, economy, ecology and environment due to the climate change.As it is known to us, water is the carrier of all the lives on the earth. Its resource and quality is an important issue for the continuous socio-economic development, especially for those regions with week ecologic environment but high population. North China (NC) lies in the drought and semi-drought area and in the northern regime of summer wind belt. It has vast territory and rich resource and is the centre of politics, economics & culture in China. Since it belongs to the Climate frail area, it is very sensitive to the climate change. Since the middle of 1960s, the precipitation keeps decreasing, much obviously from 1980s to 1990s, which causes the water shortage of this area and drought tendency in the last 50 years. The total water resource is around 50 billion cubic meters and only 60.9 percent of which can be used. Hailuanhe river basin has an average water shortage of 25.2 billion cubic meters (50% guarantee rate) for many years, 0.15 billion cubic meters for the area in Beijing, Tianjin and Tangshan. The shortage of the water resource in this area limits the economic development significantly. The water resource is only 422 cubic meters per capita or 429 cubic meters per unit area. It is much less than the national average of 2,300 cubic meters per capital and also less than the global recognized marginal average of 1,000 cubic meters for sustainable regional development. The significant decline of river flow in the mountainous region, serious decrease of water resource and over extraction ofgroundwater are the main three problems presently in the North China. Will the draught tendency remain in the next few years? When will the situation change? How is the future situation of the water resource? There are the important problems that a lot of people are aware of.Therefore, this article researches the land, air and water cycle in the North China. It follows the international research trend, and strengthens the combination between climatology and hydrology. It is a helpful discovery for our national weather-hydrology coupling research and is also an international front research topic. At present, in the North China, especially the area of Beijing, Tianjin and Tangshan, the water shortage is very serious. The present water resource doesn't satisfy the water demand. With the decreasing population and rapid economic development, water resource has been a limitation factor for the socio-economic development of the region. Drought and water shortage restrict the sustainable development in North China. Therefore, it is urgent and necessary to research the time space change and natural vibration property of the precipitation in North China. It is also to simulate and analyze the water cycle due to the current and future climate change. The research in this article will help us to learn more about the water cycle in the North China. It is a new research topic for the North China sustainable development and can provide the scientific basis for the construction and protection of the ecology and environment in North China. It can provide the guidance for the drafting of North China's socio-economic development plan. It has not only its scientific value, but also its application meaning. The main results and conclusion insist of the following aspects.1 )It can be seen from the analysis of the time array, before 1950s, in the North China, the alternate occurrence between drought and flood was quite frequent and the amplitude of precipitation change was also quite large. However, since 1960s, the amplitude is much smaller and still keeps decreasing. From the aggregated standard curve and the Mann-Kendall curve, it can be observed that the precipitation in the North China is quite periodic. And there were two rapid changes in the 1910s and 1960s. By using the power spectrum, the result shows obviously that the precipitation array has a QBO period of two years and a change period of 20 years (18.677 years). The result obtained by using thesmall wave parameters agrees with that of the power spectrum method. The precipitation has the change periods including a generation period (around 60 years), a decade period (around 10 to 20 years) and a year period (2 to 5 years). The main drought and flood periods in the 20 century resulted from the jointly affects of the yearly change and decadal change of the precipitation. Particularly, the heavy drought occurred in the period, when the little precipitation period of both the decadal change and yearly change occurred. Since 1980s, the situation gets better gradually. It is expected that it will be changed to a rich rain period after 2020.2) The North China is then categorized into 6 regions by using a rough division method. The precipitation of each region is analyzed separately. The results show that every region has an obvious period. And the period in different region is much different. In the southeast region where the water resource is richer and in Beijing, Tianjin and Tanshan area, the decadal period is quite obvious; while in the northeast and west where the water resource is scarce, the yearly period is quite obvious. This causes the different situation for the precipitation in the future in the different regions. Seen from the precipitation tendency, North China may still have little precipitation from 2000 to 2005. The precipitation will be much more than usual years between 2005 and 2010. But it will occur a drought period from 2010 to 2015. After 2015, the precipitation will increase. The situation of water shortage will alleviate.3) Climate change is an important reason for the change of water resource in the North China. Water vapor transfer is one of the main factors of the precipitation. It can be obtained from the analysis that the water vapor transfer has the feature of obvious decadal change and it happened in the middle of 1960s. The water vapor transfer in North China is affected by the strength of the monsoon and mainly in the longitude direction. Overall speaking, the longitudinal water vapor transfer capacity was relatively large before 1965. After 1965, it kept decreasing. The year of 1976 was another turning point. The longitudinal water vapor transfer capacity decreased more. And the latitudinal water vapor transfer is quite similar. But the capacity is much less and the turning point in 1976 was not that obvious. The biggest influence to the water vapor transfer of North China comesfrom the water vapor transfer of the middle south peninsula. Besides, the water vapor transfer from the southeast monsoon of the south side of the west Pacific and the activity of the cold atmosphere in the Northwest China also affect the water vapor transfer of the North China. It indicates that the continuous drought in the North China mainly results from the decrease of the water vapor due to the decadal change of the atmospheric circulation. That causes the little precipitation and shortage of water resource.4)It uses the mathematical coupling model of the atmospheric motion pattern and soil water transportation pattern in a limited area. It adopts four processes i.e., surface water evaporation, permeation, vegetation's transpiration and root water absorbing function and ground wind field, as the coupling plan of the model and simulates and calculates the drought process from July 13 to August 3, 1997 in North China. It objectively describes the process of the drought resulted from the continuously rainless and high temperature weather. The drought process involves 3 stages. In the first stage, the soil can provide the water for the crops. In the second stage, the root system level soil provides the water less than that the crops demand. In the last stage, there is no water provided to the crops.5) It uses the results from different GCM model. Based on VIC, it analyzes the future change of the water cycle in different climate. It predicts that the precipitation in the Haihe river basin increases by 14.3% in 2030 but the runoff will decrease by 6.18%. The reason can be explained in the following. The temperature increases 2 centigrade degrees every year, which makes the evaporation increased by 21.1% so that it cancels the increase of the precipitation. Therefore, the water resource in the Haihe river basin will be even much scarcer and the situation will be more serious in the future.
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