变暖背景下青藏高原夏季风变异及其对中国西南气候的影响

利用1951—2012年逐月NECP/NCAR-Ⅰ再分析资料和1960—2012年逐月中国西南地区116站常规气象要素资料,基于青藏高原地区夏季600 hPa涡度场特征,定义了新的青藏高原夏季风强度和位置指数,讨论在全球变暖背景下,青藏高原季风变化对中国西南地区气候的影响。青藏高原季风强度整体增强,在20世纪90年代末达到峰值后逐渐减弱,与北半球气温变化具有较好的一致性,位置变化相对独立。夏季青藏高原季风强度和中心经度位置对中国西南地区气候有显著影响。当青藏高原季风偏强时,西南地区水汽异常辐合,以阴天为主,日照偏短,蒸发减弱,气温日较差明显减小,降水偏多;上升运动在川渝地区发展深厚,云贵地区仅限于600 hPa以下,川渝地区气象要素变化更显著。当青藏高原季风位置偏东时,西南全区受异常下沉运动控制,气温偏高,四川中、西部和贵州、广西等地出现较强的水汽异常辐散,气温显著偏高,相对湿度偏低,降水偏少。进入21世纪以来,青藏高原季风强度和中心经度的反位相叠加,加剧了西南地区的干旱化。新的青藏高原季风指数不仅能反映青藏高原地区的季风环流特征,而且对中国西南气候变化具有较好的指示意义,可为中国汛期气候预测提供理论依据和技术支持。

How Well does BCC_CSM1.1 Reproduce the 20th Century Climate Change over China?

The historical simulation of phase five of the Coupled Model Intercomparison Project （CMIP5） ex- periments performed by the Beijing Climate Center cli- mate system model （BCC_CSM1.1） is evaluated regard- ing the time evolutions of the global and China mean sur- face air temperature （SAT） and surface climate change over China in recent decades. BCC CSM1.1 has better capability at reproducing the time evolutions of the global and China mean SAT than BCC_CSM1.0. By the year 2005, the BCC_CSM1.1 model simulates a warming am- plitude of approximately I℃ in China over the 1961- 1990 mean, which is consistent with observation. The distributions of the warming trend over China in the four seasons during 1958-2004 are basically reproduced by BCC CSM1.1, with the warmest occurring in winter. Al- though the cooling signal of Southwest China in spring is partly reproduced by BCC_CSM1.1, the cooling trend over central eastern China in summer is omitted by the model. For the precipitation change, BCC_CSM1.1 has good performance in spring, with drought in Southeast China. After removing the linear trend, the interannual correlation map between the model and the observation shows that the model has better capability at reproducing the summer SAT over China and spring precipitation over Southeast China.

Influences of air CO2 on hydrochemistry of drip water and implications for paleoclimate study in a stream-developed cave, SW China

Cave air CO_2 is a vital part of the cave environment. Most studies about cave air CO_2 variations are performed in caves with no streams; there are few studies to date regarding the relationship of cave air CO_2 variations and drip water hydrochemistry in underground stream–developed caves. To study the relationship of underground stream, drip water, and cave air CO_2, monthly and daily monitoring of air CO_2 and of underground stream and drip water was performed in Xueyu Cave from 2012 to 2013.The results revealed that there was marked seasonal variation of air CO_2 and stream hydrochemistry in the cave. Daily variations of cave air CO_2, and of stream and drip water hydrochemistry, were notable during continuous monitoring.A dilution effect was observed by analyzing hydrochemical variations in underground stream and drip water after rainfall. High cave air CO_2 along with low p H and low δ^(13)C DIC in stream and drip water indicated that air CO_2 was one of the dominant factors controlling stream and drip water hydrochemistry on a daily scale. On a seasonal scale, stream flows may promote increased cave air CO_2 in summer; in turn, the higher cave air CO_2 could inhibit degassing of drip water and make calcite δ^(13)C more negative. Variation of calcite δ^(13)C(precipitated from drip water) was in reverse of monthly temperature, soil CO_2, and cave air CO_2. Therefore,calcite δ^(13)C in Xueyu Cave could be used to determine monthly changes outside the cave. However, considering the different precipitation rate of sediment in different seasons,it was difficult to use stalagmites to reconstruct environmental change on a seasonal scale.

Observed Climate Changes in Southwest China during 1961-2010

The present study focused on statistical analysis of interannual, interdecadal variations of climate variables and extreme climate events during the period of 1961-2010 using observational data from 376 meteorological stations uniformly distributed across Southwest China, which includes Yunnan, Guizhou, Chongqing, Sichuan and Tibet. It was found that temperatures in most of the region were warming and this was especially evident for areas at high elevation. The warming was mostly attributable to the increase in annual mean minimum temperature. The characteristics of high temperature/heat waves are increase in frequency, prolonged duration, and weakened intensity. Annual precipitation showed a weak decreasing trend and drier in the east and more rainfall in the west. The precipitation amount in flood season was declining markedly in the whole region; rainfall from extreme heavy precipitation did not change much, and the portion of annual precipitation contributed by extreme heavy precipitation had an increasing trend; annual non-rainy days and the longest consecutive non-rainy days were both increasing; the extreme drought had a decreasing trend since the 1990s; the autumn-rain days displayed a downward fluctuation with apparent periodicity and intermittency. The number of southwestern vortices was decreasing whereas the number of moving vortices increased.

Climate Change in Southwest China during 1961–2010:Impacts and Adaptation

Due to climate change, the regional agro-climatic conditions in Southwest China have undergone changes. The heat sources for the growth of crops have been improved. The number of days with temperatures steadily above 0℃ and 10℃ （two criteria） have increased during 1960-2010. The area suitable for multiple cropping has increased; the growth period has shortened; the climatic potential productivity has declined; the pest damage has worsened. During 1986-2010, the desired cooling degree days in Southwest China has increased at 38.9℃ d per decade. Forest fires and pests have increased. The area of meadow and wetlands has decreased. Heterogeneous invasion has intensified; endangered animal and plant species have increased. The tourism landscape has been damaged.＇ The risk of human health has increased. In the 21st century, with the increase of temperature and precipitation, the number of days with temperature steadily above 10℃ and the accumulated temperature will continue to increase, most notably in the Qinghai-Tibetan Plateau. The area of intercropping will expand; multiple cropping will move to higher altitudes. The impacts of agro- meteorological disasters, pests and diseases will intensify. The summer cooling energy consumption continues to increase; energy supply will show larger variability; the gap between energy supply and demand will be widened. The phenology will keep on changing, and the habitat will be worsening. Biological population will move northward and to higher altitudes. Some species are at risk of extinction. Negative effects on health will increase.

Holocene Temperature Records from the East China Sea Mud Area Southwest of the Cheju Island Reconstructed by theU_(37)~K~' and TEX_(86) Paleothermometers

As an important marginal sea under the influences of both the Changjiang River and the Kuroshio, the East China Sea （ECS） environment is sensitive to both continental and oceanic forcing. Paleoenvironmental records are essential for understanding the long-term environmental evolution of the ECS and adjacent areas. However, paleo-temperature records from the ECS shelf are currently very limited. In this study, the U^K_37 and TEX86 paleothermometers were used to reconstruct surface and subsurface temperature changes of the mud area southwest of the Cheju Island （Site F10B） in the ECS during the Holocene. The results indicate that temperature changes of F 10B during the early Holocene （11.6-6.2 kyr） are associated with global climate change. During the period of 6.2-2.5 kyr, the similar variability trends of smoothing average of AT （the difference between surface and subsurface temperature） of Site F10B and the strength of the Kuroshio suggest that the Kuroshio influence on the site started around 6.2kyr when the Kuroshio entered the Yellow Sea and continued to 2.5 kyr. During the late Holocene （2.5-1.45 kyr）, apparent decreases of U^K_37 sea surface temperature （SST） and AT imply that the direct influence of the Kuroshio was reduced while cold eddy induced by the Kuroshio gradually controlled hydrological conditions of this region around 2.5 kyr.

Can Artificial Climate Trends in Global Reanalysis be Reduced by Dynamical Downscaling:A Case Study of China

In this study, the ability of dynamical downscaling for reduction of artificial climate trends in global reanalysis is tested in China. Dynamical downscaling is performed using a 60-km horizontal resolution Regional Integrated Environmental Model System （RIEMS） forced by the NCEP-Department of Energy （DOE） reanalysis II （NCEP-2）. The results show that this regional climate model （RCM） can not only produce dynamically consis- tent fine scale fields of atmosphere and land surface in the regional domain, but it also has the ability to minimize artificial climate trends existing in the global reanalysis to a certain extent. As compared to the observed 2-meter temperature anomaly averaged across China, our model can simulate the observed inter-annual variation and variability as well as reduce artificial climate trends in the reanalysis by approximately 0.10℃ decade-1 from 1980 to 2007. The RIEMS can effectively reduce artificial trends in global reanalysis for areas in western China, especially for regions with high altitude mountains and deserts, as well as introduce some new spurious changes in other local regions. The model simulations overesti- mated observed winter trends for most areas in eastern China with the exception of the Tibetan Plateau, and it greatly overestimated observed summer trends in the Si- chuan Basin located in southwest China. This implies that the dynamical downscaling of RCM for long-term trends has certain seasonal and regional dependencies due to imperfect physical processes and parameterizations.

General characteristics of climate changes during the past 2000 years in China

The general characteristics of climate changes over the past 2000 years in China,regional differences and uncertainties were analyzed based on the recently peer-reviewed high time-resolution climatic reconstructions.The results showed that there exists four warm periods of the temperature variation in China since the Qin Dynasty,including the western and eastern Han Dynasties(200 BC-AD 180),the Sui and Tang dynasties(541-810),the Song and Yuan dynasties(931-1320),and the 20th century,and three cold phases involving the Wei,Jin,and North-South Dynasties(181-540),the late Tang Dynasty(811-930),and the Ming and Qing dynasties(1321-1920).The Song and Yuan warm period is consistent with the Medieval Warm Period over the Northern Hemisphere,and the cold phases of the North-South Dynasties and the Ming and Qing dynasties are paralleled to the Dark Ages Cold Period and the Little Ice Age,respectively.The 13th-15th century could be a shift to the wet condition of the climate,and the low precipitation variability is exhibited in western China prior to 1500.In the context of the climate warming,the pattern of the drought in north and flood in south is prevalent over the eastern China.In addition,the published reconstructions have a high level of confidence for the past 500 years,but large uncertainties exist prior to the 16th century.

Climate change regionalization in China(1961–2010)

Since climatic condition is the important foundation for human subsistence and development and the key factor in sustainable development of economy and society, climate change has been a global issue attracting great attentions of politicians, scientists, governments, and the public alike throughout the world. Existing climate regionalization in China aims to characterize the re gional differences in climate based on years of the mean value of different climate indexes. However, with the accelerating climate change nowadays, existing climate regionalization cannot represent the regional difference of climate change, nor can it reflect the disasters and environmental risks incurred from climate changes. This paper utilizes the tendency value and fluc tuation value of temperature and precipitation from 1961 to 2010 to identify the climate change quantitatively, and completes the climate change regionalization in China （1961-2010） with county administrative regionalization as the unit in combination with China＇s terrain feature. Level-I regionalization divides China＇s climate change （1961-2010） into five tendency zones based on the tendency of temperature and precipitation, which are respectively Northeast China-North China warm-dry trend zone, East China-Central China wet-warm trend zone, Southwest China-South China dry-warm trend zone, Southeast Ti- bet-Southwest China wet-warm trend zone, and Northwest China-Qinghai-Tibet Plateau warm-wet trend zone; level-lI region- alization refers to fourteen fluctuation regions based on level-I regionalization according to the fluctuation of temperature and precipitation.