"limate Change and Water", the IPCC technical paper contribution to the IPCC Fourth Assessment Report (AR4) was launched on 8th April 2008. Based on three assessment reports of the IPCC AR4, this technical paper summarizes the newest peer-reviewed and comprehensive findings from international scientific communities on climate change and water for past, present and future. The robust key findings are: observed global warming over several decades has been linked to large-scale changes in the large-scale hydrological cycle. Climate models simulations for the 21st century are consistent in projecting precipitation increases at high latitudes and in parts of the tropics, and decreases while in some subtropical and lower mid-latitude regions. By the middle of the 21st century, annual average river runoff and water availability are projected to increase as a result of climate change at high latitudes and in some wet tropical areas, and decrease over some dry regions at mid-latitudes and in the dry tropics. Increased precipitation intensity and variability is projected to increase the risks of flooding and drought in many areas. Water supplies stored in glaciers and snow cover are projected to decline in the course of the century. Higher water temperatures, and changes in extremes, including floods and droughts are projected to affect water quality and exacerbate many forms of water pollution. Globally, the negative impacts of future climate change on freshwater systems are expected to outweigh the benefits. Changes in water quantity and quality due to climate change are expected to affect food availability, stability, access, and utilization. Climate change affects the function and operation of existing water infrastructure-including hydropower, structural flood defenses, drainage, and irrigation systems-as well as water management practices. Current water management practices may not be robust enough to cope with the impacts of climate change. Climate change challenges the traditional assumption that past hydrological experience provides a good guide to future conditions. Adaptation options designed to ensure water supply during average and drought conditions require integrated demand-side as well as supply-side strategies. Mitigation measures can reduce the magnitude of impacts of global warming on water resources, in turn reducing adaptation needs. Water resources management has clear impacts on many other policy areas.

By using the precipitation data of meteorological stations in the Xijiang River basin, and time series of the flood peak water levels of the mainstream and tributaries of the Xijiang River in 1959-2008, the data sets of yearly flood occurrence times were developed, and the spatial and temporal characteristics of the flood occurrence times and their evolution laws were analyzed. The results indicate that the flood frequency in the mainstream region of the Xijiang River was higher than those in the tributary regions, and the flood frequency in the lower reaches of the tributaries was higher than that in the upper reaches. The flood occurrence times had a prominent stage characteristic and some significant abrupt changes, the main abrupt changes happened in 1967 and 1993. Moreover, the floods occurred more frequently in recent 15 years; the basin-wide disastrous floods mainly concentrated in this period. Studying the flood laws in the Xijiang River basin is beneficial for raising the level of flood disaster evaluation and prediction, and for providing a scientific basis for hazard mitigation and prevention.

The extreme precipitation index (R5d) over Chongqing for the 21st century projected by the global climate system models participating in the fourth assessment report of IPCC under the SRES A2, A1B and B1 scenarios has been analyzed in this paper. The results show that compared to the current (1980-1999) climate , R5d over Chongqing will increase in most time of the 21st century under the three SRES scenarios. Especially, R5d will increase more significantly in the later 21st century than in the early and middle 21st century.

The recent years saw rapid progress in the research of the impact of climate change on national security in the United States. The article aims to provide a general assessment of the current status and the major characteristics of U.S. research of the impact of climate change on national security and to analyze what experience we can learn from the United States. The author argues that so far in what ways and to what extent climate change would influence U.S. national security has been fully discussed in the United States; and there have also been rich studies of the countermeasures against the threat of climate change to U.S. national security. The major features of current U.S. research are: first, there are some innovations in terms of theories and research methods. Second, the research boasts global vision and strong relevance to U.S. national security. Third, the academic level is improved steadily. Forth, the network of government, academia and think tanks has taken shape in U.S. current research. Currently, the similar research in China is still in its infancy. To promote China's research of the impact of climate change on national security, we should draw some useful experience from the U.S. practices.

Differences and synergies between the mitigation and adaptation of climate change in climate policies are analyzed in this paper; the evolution of the two key factors, i.e. mitigation and adaptation, of climate policies and their close relationships with sustainable development are reviewed; and the importance of the synergies of multi-factors is pointed out. The analysis emphasizes that more attention should be paid to the implementation of climate policy, that is to say, it should be brought into national and sectoral development policies. In the end, it is pointed out that to ensure the synergies of multi-objectives in climate policies, three issues need to be well addressed: how to determine various objectives of climate policies, how to develop the corresponding capacity necessary for ensuring the synergic implement of multi-objectives and how to combine the existing management mechanism and sectoral investment together.

The road from Bali to Copenhagen will be tough but promising for a global deal to address climate change. Global target and share of country responsibility, climate change mitigation and adaptation, technology and financial support will be the key elements for the post-2012 international climate regime. Based on the synthetic analysis and progress review of the key elements, the authors analyze China's post-2012 strategy under such a changing regime, and under the changing circumstances of domestic and international politics, economy, environment and society.

China's large population and rapid economic development lead to large recent increase in CO2 emissions, which is expected to continue in the next few decades. The conflict of economic development and environment protection poses one of the greatest challenges facing China and the world. However, climate change also provides opportunities for China to lead to a comprehensive sustainable pathway through renewable energy development, reforestation and construction of high-energy-efficiency infrastructure.

China's vehicle transportation is now facing up to dual pressure: fuel shortage and GHGs emission increase. Based on the background of China's rapid development and gaps in average vehicle fuel economy between China and developed countries, by analyzing the technology options for automakers, we established an analysis framework on the fuel consumption and GHGs emission of vehicle transportation, and drew the conclusion that in order to control the overall fuel consumption of vehicle transportation, a series of technology and policy measures should be adopted so as to control the vehicle volume, reduce the average mileage of vehicles and improve the fuel economy of single vehicle. At the end of this paper, we analyzed and commented on the presented integrated policy package which aimed to reduce the overall fuel consumption & GHGs emission of vehicle transportation.

The impact of and adaptation to climate change has become an urgent issue for agriculture production. The temperature increased 1.5℃ in Northeast China (NEC) during the past 50 years, the increment is apparently higher than the average value over the whole China. Climate change brought about complicated impacts on crop production. NEC is one of the most important crop production bases in China; it takes a big role for food safety and security of China. It is of significance to discuss adaptation of agriculture to climate change on regional scale. The main characters of climate change and their impacts on agriculture in NEC during the past 50 years were analyzed in this study; the strategies and measures for adapting to and mitigating climate change in NEC are put forward, according to the impacts of GHGs emission and land-use in human activities on climate change. We emphasize that we should take positive action in agro-ecology, water resources utilization and environment protection, so as to protect the climate-environment and to fully utilize climate resources, thus to help the sustainable development of grain production in NEC.

The characteristics and changes of arid climate, including temperature, precipitation and other factors, such as drought frequency and soil moisture, were analyzed for 1960-2005 in Tianshui, Gansu Province. The results indicate that precipitation in the 1990s was the least in recent 50 years, the change rate of precipitation has increased obviously since the 21st century. Temperature has increased generally since the 1960s, especially in the 1990s. The soil moisture was the lowest and in serious deficit; and spring drought, early summer drought and midsummer drought occurred more frequently in the 1990s. According to the change characteristics of arid climate and their effects on the growth of grain crops, the influence coefficient of drought to the yield of grain crops was introduced, and levels of the planting risk of main summer and autumn crops were also assessed. Finally, a plan of planting structure adjustment for main grain crops adapting to changes in arid climate is also provided based on a linear risk decision model.