Early proxy-based studies suggested that there potentially occurred a "southern drought/northern flood"(SDNF) over East China in the mid-Holocene(from roughly 7000 to 5000 years before present). In this study, we used both global and regional atmospheric circulation models to demonstrate that the SDNF—namely, the precipitation increases over North China and decreases over the the lower reaches of the Yangtze River Valley—could have taken place in the mid-Holocene. We found that the SDNF in the mid-Holocene was likely caused by the lower SST in the Pacific. The lowered SST and the higher air temperature over China's Mainland increased the land–sea thermal contrast and, as a result, strengthened the East Asian summer monsoon and enhanced the precipitation over North China.
利用WRF(Weather Research and Forecasting)模式,进行了我国东北地区冬季降雪的高分辨率数值模拟,评估了WRF模式对季节降雪的模拟能力,并探讨了模式水平分辨率和物理过程参数化方案对降雪模拟的影响.结果显示WRF模式可以合理地模拟冬季气温和降水的空间分布,模拟结果和观测吻合较好.该模式可以合理地模拟东北地区季节降雪的空间分布和时间演变,显示了该模式较强的模拟性能.水平分辨率和物理过程参数化方案对降雪模拟有重要影响,高分辨率模拟结果更接近观测;相对于积云对流参数化方案,模式对陆面过程和微物理过程参数化方案更加敏感.
Observed winter(December–February)surface air temperature over East Asia(0°–60°N,100–140°E)(TEA)shows non-uniform variation during 1979–2013,with cooling and weak warming north and south of40°N.To understand this,the authors perform statistical analysis(linear regression and composite)on the observed data.The results suggest that reduced(increased)autumn sea ice cover in the Barents-Kara Sea(BK-ASIC)lowers(warms)TEA over northern East Asia,which is consistent with previous studies.In comparison,increased(decreased)winter sea ice cover in the Sea of Okhotsk(O-WSIC),warms(cools)the air over southern East Asia.The mechanism can be described as follows:When the BK-ASIC decreases,the East Asian winter monsoon tends to be stronger with an intensified Siberian high,leading to cooling over northern East Asia.An O-WSIC increase is associated with cold anomalies north of 50°N,altering the meridional temperature gradient between the midlatitudes and tropics,and leading to a northward shift of the East Asian jet steam in the upper troposphere.In the low atmosphere,anomalous northeasterly winds prevail north of50°N and anomalous southerly winds control the southern coast of East Asia,contributing to the weak warming over southern East Asia.Version 3 of the Community Atmosphere Model also provides evidence for the impact of increased O-WSIC on the warm southern mode of TEA.
In this paper we report an analysis of sampling error uncertainties in mean maximum and minimum temperatures(Tmax and Tmin) carried out on monthly, seasonal and annual scales, including an examination of homogenized and original data collected at 731 meteorological stations across China for the period 1951–2004. Uncertainties of the gridded data and national average, linear trends and their uncertainties, as well as the homogenization effect on uncertainties are assessed. It is shown that the sampling error variances of homogenized Tmax and Tmin, which are larger in winter than in summer, have a marked northwest–southeast gradient distribution, while the sampling error variances of the original data are found to be larger and irregular. Tmax and Tmin increase in all months of the year in the study period 1951–2004, with the largest warming and uncertainties being 0.400℃(10 yr)-1±0.269℃(10 yr)-1and 0.578℃(10 yr)-1±0.211℃(10 yr)-1in February, and the least being 0.022℃(10 yr)-1±0.085℃(10 yr)-1and 0.104℃(10 yr)-1±0.070℃(10 yr)-1in August. Homogenization can remove large uncertainties in the original records resulting from various non-natural changes in China.
Based on 150-year simulations of a regional climate model, RegCM3, under the Special Report on Emissions Scenarios (SRES) A1B scenario, the effective drought index (EDI) is used to project the future drought change in China. During the baseline period 1986-2005, RegCM3 was found to reliably simulate the spatial pattern of drought over the country. Over the 21st century, the regionally averaged EDI should increase, corresponding to a decrease of drought, while the probability of extreme drought events should increase. Geographically, drought should clearly increase in Northeast China, the middle and lower reaches of the Yangtze River valley, Southwest China, and southern Tibet but decrease in most parts of the rest of the country.
In permafrost areas, the timing of thermal surface settlement hazard onset is of great importance for the construction and maintenance of engineering facilities.Future permafrost thaw and the associated thermal settlement hazard onset timing in the Qinghai-Tibet engineering corridor(QTEC) were analyzed using high-resolution soil temperature data from the Community Land Model version4 in combination with multiple model and scenario soil temperature data from the fifth phase of the Coupled Model Intercomparison Project(CMIP5). Compared to the standard frozen ground map for the Tibetan Plateau and ERAInterim data, a multimodel ensemble reproduces the extent of permafrost and soil temperature change in the QTEC at a 1 m depth from 1986–2005. Soil temperature and active layer thickness increase markedly during 2006–2099 using CMIP5 scenarios. By 2099, the ensemble mean soil temperature at 15 m depth will increase between 1.0 and 3.6 ℃ in the QTEC. Using crushed-rock revetments can delay the onset of thermal settlement hazard for colder permafrost areas by approximately 17 years in the worst case scenario of RCP8.5. Nearly one-third of the area of the QTEC exhibits settlement hazard as early as 2050, and half of this one-third of the area is traversed by the QinghaiTibet highway/railway, a situation that requires more planning and remedial attention. Simulated onsets of thermal settlement hazard correspond well to the observed soil temperature at 15 m depth for seven grid areas in the QETC, which to some extent indicates that these timingestimates are reasonable. This study suggests that climate model-based timing estimation of thermal settlement hazard onset is a valuable method, and that the results are worthy of consideration in engineering design and evaluation.
