Eastern Northwest China Research Articles

Characteristics and comparative analysis of the reconstructed drought/flood grade sequence of eastern Northwest China from 1470 to 1912

The eastern Northwest Chinese drought/flood grade sequence was reconstructed according to historical data on drought and flood disasters for the period from 1470 to 1912. The changing characteristics of drought/flood disasters over 443 years in eastern Northwest China were analyzed by employing methods such as the moving average, accumulative anomaly, moving t test, and wavelet analysis. To verify the reliability of this sequence, long-term trends were analyzed and compared using precipitation sequences reconstructed for Huashan and the drought/flood index for Longxi. The drought/flood grade curve and stalagmite oxygen isotopic records of two provinces were also compared. The results show that: (1) drought disasters were severe and frequent in eastern Northwest China. An alternating pattern between drought and flood occurrences was observed, which can be divided into four stages: 1470–1540, 1541–1615, 1616–1796, and 1797–1912. We further classified the four stages into 12 partial drought or partial flood periods. (2) Twelve abrupt changes were observed on the decadal scale and five abrupt changes were detected on the half-century scale. (3) The reconstructed sequences display a periodic variability on multiple scales; notable variability was detected on the following timescales: 130–110 years, 70–80 years, 50–52 years, 28 years, 10–15 years, and 5 years. The first four primary periods were 28 years, 15 years, 73 years, and 5 years; 28 years shows the strongest oscillation. (4) Based on the comparison and analysis, the reconstructed drought/flood grade sequence is highly consistent with other precipitation sequences. It corresponds to stalagmite oxygen isotopes records of the same period. All these findings indirectly confirm the reliability of the recovered historical flood and drought grade sequence based on historical data.

Extreme precipitation events during 1960–2011 for the Northwest China: space-time changes and possible causes

Spatial and temporal patterns in precipitation indices across Northwest China (NWC) during 1960–2011 were investigated using 11 previously defined indices. Results show that more than 50% of stations for wet-related indices exhibit increasing trends and the largest increases appear in winter, while 72.1% of stations display decreasing trends for consecutive dry days. The observing sites with positive trends are mainly distributed over mid-western NWC and northwestern Xinjiang, while the declining trends are concentrated in eastern NWC. Very wet days account for 23% of the total rainfall on average, combined with similar patterns of spatial distribution between annual total rainfall and precipitation extremes, suggesting that extreme, rather than moderate, precipitation moderates the variations in total rainfall. After the mid-1980s, the NWC exhibits a wetting tendency, and precipitation extremes tend to increase with larger magnitudes and fluctuations. During 1987–2011, the prevailing eastward wind field anomalies at 850 hPa and statistically significant increasing trends of geopotential height are found over the Eurasian continent from spring to autumn, together with enhanced anticyclonic circulation near 47° N and 100° E, providing favorable conditions for the occurrence of extreme precipitation events over NWC. While the circulation pattern in winter is distinct compared with other seasons, a convergence between eastward wind anomalies and southeasterly winds favors significantly positive increases in precipitation extremes. The well-organized wave train-like structures originated from the North Atlantic travel through Europe and central Asia and impact the precipitation extremes over NWC from spring to autumn during 1987–2011. Similar to wind field anomalies, the southeasterly water vapor fluxes are remarkable in winter. Generally, the approximately opposite circulation patterns dominate during 1960–1986 in comparison with those during 1987–2011.

Assessment of the quality of NCEP-2 and CFSR reanalysis daily temperature in China based on long-range correlation

The daily temperatures from observational data, NCEP-2 and CFSR reanalysis data all exhibit long-range correlation (LRC) characteristics, which provides a test bed for assessing the reliability of reanalysis data. In this study, the quality of the NCEP-2 and CFSR data in China are evaluated on the basis of the LRC characteristics of daily temperatures, including daily average temperature (DAT), daily maximum temperature (DMAT), daily minimum temperature (DMIT), and diurnal temperature range (DTR). Compared with the observations, the quality of NCEP-2 daily temperature is relatively good in central and eastern Northwest China, and most of central and eastern China, especially for NCEP-2 DMAT. However, the NCEP-2 reanalysis data as well as CFSR has a significant difference with the LRC of the observations in most of Sichuan, Qinghai-Tibet Plateau and some areas of southwestern Xinjiang at a significance level of Alpha = 0.05. In general, the LRC characteristics of NCEP-2 daily temperature perform better than that of CFSR data. As far as DAT is concerned, CFSR perform worse in central and eastern Northwest China, and better than NCEP-2 only in South China and eastern Jiangnan. The quality of the CFSR DMAT is worse than that of NCEP-2 in central and eastern Northwest China, western Inner Mongolia, and eastern China. The quality of NCEP-2 DMIT is better than CFSR in central and eastern Northwest China, most of Inner Mongolia, and is worse than it in most of South China and eastern Jiangnan. The reliability of the CFSR DTR is very low in most of China.

Study of Changing Features of Precipitation from 1900-2010 Years in Africa-Asia Arid and Semi-Arid Area

The relationship between time-space variation characteristics and the variation of the general atmospheric circulation of rainfall occurred in Asia, Africa through North Africa-Middle East-Western Middle Asia-Eastern Middle Asia, Northwest China-Eastern Northwest China-North China and Northeast China is studied based on the analysis of GPCC rainfall data from 1901 to 2010 and annual precipitation in relevant cities of China from 1901 to 2010, and the data of NCEP of surface pressure as well as 500 Hpa potential high from 1950 to 2010. The result shows that the total precipitation presents a decreasing trend in north Africa to the northeast of China in recent 100 years. It has a mutation in 1950s. The precipitation presented a decreasing trend in North Africa and Middle East, in recent 100 years; it presented a further decreasing trend after 1950s. It presented a decreasing trend before 1950s and an increasing trend after 1950s in Middle Asia and Northwest china. It also presented a decreasing trend before 1950s and an increasing trend between 1950s to 1990s, and decreased later in Eastern Northwest China, North China and Northeast China which also presented in a more or less period in different areas from North Africa to Northeast China. The beginning of less precipitation years and less period occurred after it presented less period in north Africa in time and space. After it moved to the east areas as the year past, at last, the SLPA fields which presented more or less precipitations of years from North Africa to Northeast China were analyzed. It also shows that the SLPA fields which presented more were beneficial to the precipitations and presented negative effects of precipitations in the polar, high and mid- and lower latitudes.

Analysis of China’s Haze Days in the Winter Half-Year and the Climatic Background during 1961–2012

The characteristics of haze days and the climatic background are analyzed by using daily observations of haze, precipitation, mean and maximum wind speed of 664 meteorological stations for the period of 1961–2012. The results show that haze days occur significantly more often in eastern China than in western China. The annual number of haze days is 5–30 d in most parts of central-eastern China, with some areas experiencing more than 30 d, while less than 5 d are averagely occurring in western China. Haze days are mainly concentrated in the winter half-year, with most in winter, followed by autumn, spring, and then summer. Nearly 20% of annual haze days are experienced in December. The haze days in central-eastern China in the winter half-year have a significant increasing trend of 1.7 d per decade during 1961–2012. There were great increases in haze days in the 1960s, 1970s and the beginning of the 21st century. There was also significant abrupt changes of haze days in the early 1970s and 2000s. From 1961 to 2012, haze days in the winter half-year increased in South China, the middle-lower reaches of the Yangtze River, and North China, but decreased in Northeast China, eastern Northwest China and eastern Southwest China. The number of persistent haze is rising. The Longer the haze, the greater the proportion to the number persistent haze. Certain climatic conditions exacerbated the occurrence of haze. The correlation coefficient between haze days and precipitation days in the winter half-year is mainly negative in central-eastern China. The precipitation days show a decreasing trend in most parts of China, with a rate of around –4.0 d per decade in central-eastern China, which reduces the sedimentation capacity of atmospheric pollutants. During the period of 1961–2012, the correlation coefficients between haze days and mean wind speed and strong wind days are mainly negative in central-eastern China, while there exists positive correlation between haze days and breeze days in the winter half-year. The mean wind speed and strong wind days are decreasing, while breeze days are increasing in most parts of China, which is benefitial to the reduction of the pollutants diffusion capacity. As a result, haze occurs more easily. CitationSong, L.-C., R. Gao, Y. Li, et al., 2014: Analysis of China’s haze days in the winter half-year and the climatic background during 1961–2012.Adv. Clim. Change Res.,5(1), doi: 10.3724/SP.J.1248.2014.001.

A Primary Probe on the County Cultural Facility’s Suitability Indicator System in Eastern Northwest China — Case Analysis on Chengcheng County, Shaaxi Province

In relation to comprehensive living standard and public interests, urban cultural facility poses major influence on urban life. Compared with urban cultural facility, county cultural facility is the vinculum linking the cultural undertakings between urban and regional area, which requires rational guidance to break through the gap between urban and rural development. This thesis observed the current situation of cultural facility in Chengcheng County of Shaanxi Province, finding that the particularity of county cultural facility development and the inconsistency between supply and demand have exceeded the capacity of present development criterion. The in-depth analysis on Chengcheng County’s cultural facility is based on the influential observation of indicator system, standing on a wider perspective in consideration with resident’s demand, probing the suitable indicator system of cultural facility in Chengcheng County in consistency with the developing feature and trend combing with national standard and developing situation.

Structural variation of an atmospheric heat source over the Qinghai-Xizang Plateau and its influence on precipitation in northwest China

NCEP/NCAR reanalysis data and a 47-year precipitation dataset are utilized to analyze the relationship between an atmospheric heat source (hereafter called 〈 Q1 〉) over the Qinghai-Xizang Plateau (QXP) and its surrounding area and precipitation in northwest China. Our main conclusions are as follows: (1) The horizontal distribution of 〈 Q1 〉 and its changing trend are dramatic over QXP in the summer. There are three strong centers of 〈 Q1 〉 over the south side of QXP with obvious differences in the amount of yearly precipitation and the number of heat sinks predominate in the arid and semi-arid regions of northwest China (NWC), beside the northern QXP with an obvious higher intensity in years with less precipitation. (2) In the summer, the variation of the heat source’s vertical structure is obviously different between greater and lesser precipitation years in eastern northwest China (ENWC). The narrow heat sink belt forms between the northeast QXP and the southwestern part of Lake Baikal. In July and August of greater precipitation years, the heating center of the eastern QXP stays nearly over 35°N, and at 400 hPa of the eastern QXP, the strong upward motion of the heating center constructs a closed secondary vertical circulation cell over the northeast QXP (40°-46°N), which is propitious to add precipitation over the ENWC. Otherwise, the heating center shifts to the south of 30°N and disappears in July and August of lesser precipitation years, an opposite secondary circulation cell forms over the northeast QXP, which is a disadvantage for precipitation. Meanwhile, the secondary circulation cell in years with more or less precipitation over the ENWC is also related to the heat source over the Lake Baikal. (3) The vertical structure of the heat source over the western QXP has obvious differences between greater and lesser precipitation years in western northwest China in June and July. The strong/weak heat source over the western QXP produces relatively strong/weak ascending motion and correspondingly constructs a secondary circulation cell in lesser/greater precipitation years.