Groundwater recharge and climatic change during the last 1000 years from unsaturated zone of SE Badain Jaran Desert

The history of groundwater recharge and cli-matic changes during the last 1000 years has been estimated and reconstructed using environmental chloride from un-saturated zone profde in the southeast Badain Jaran Desert,NW China. By using a steady-state model for duplicate un-saturated zone chloride profiles, the long-term recharge at the site was estimated to be 1.3 mm yr^-1. From one profde,which reached the water table, the climatic change events of 10-20 years duration were well preserved. There were 3 wet phases and 4 dry episodes during the recent 800 years ac-cording to the peaks and troughs of recharge rate calculated via chloride concentration and moisture content. There was a dry episode before 1290 AD. At ca. 1500-1530 AD, which is an important date, there was an abrupt change from drought to wet conditions. At the beginning of the 1800s, local climate changed from wet to dry occurred and subsequently dete-riorated over the past 200 years,The unsaturated profile was compared with the Guliya ice core records.The agreement of wet and dry phases from 1200 to 1900 AD is quite good,whilst trends diverged during the last 100 years.It seems that the large-scale climate difference took place between mountain regions and the desert basin in NW China during the 20th century,which closely correspond to the water table reduction of some l metre.     

Changes of climate extremes of temperature and precipitation in summer in eastern China associated with changes in atmospheric circulation in East Asia during 1960–2008

Climate extremes and changes in eastern China are closely related to variations of the East Asian summer monsoon and corresponding atmospheric circulations.The relationship between frequencies of temperature and precipitation extremes in China during the last half century is investigated using Singular Value Decomposition analysis.During 1980-1996,there was a typical pattern with fewer hot days and more precipitation extremes in the northern part of eastern China,and more hot days and fewer precipitation extremes in the southern part.This geographic pattern tended to reverse after 1997,with fewer hot days and more extreme precipitation days south of the Yangtze River and vice versa to the north.Differences in atmospheric circulation between the former and latter periods are presented.We conclude that a mid-level anomalous high/low,upper-level anomalous easterlies/westerlies over the north/south of eastern China,a weakened East Asian summer monsoon and associated upper-tropospheric center of cooling(30°N,110°E) are all favorable for the changes in frequencies of temperature and precipitation extremes.     

Tree-ring precipitation records from Baiyinaobao,Inner Mongolia since A.D. 1838

Tree rings have attracted the wide attention of geo- environmental and climatic scientists due to its high resolution and accuracy. Lots of important results about climatic change have been obtained for the last 100 to 2000 years when it has no instrumental observation and people are very concerning about it nowadays. For example, by using tree-ring data, temperature, precipitation and drought history have been reconstructed back to hundreds of or thousands of years for different regions in th…     

The Holocene Palaeoclimatic change in southern vicinity of Tengger Desert

Through stratigraphy and chronology studies on Hongshui River section located at the southern vicinity of Tengger Desert, and based on the analysis results of TOC, TIC, elements, stable oxygen isotope that possess a high resolution of 40–50 a, the paleaoclimatic change history during last 8 000–3 000 a has been reconstructed.     

A tree-ring-based reconstruction of the Yimin River annual runoff in the Hulun Buir region, Inner Mongolia, for the past 135 years

Based on the relationships between the regional tree-ring chronology(RC) of moisture-sensitive Pinus sylvestris var.mongolica and the monthly mean maximum temperature,annual precipitation and annual runoff,a reconstruction of the runoff of the Yimin River was performed for the period 1868-2002.The model was stable and could explain 52.2% of the variance for the calibration period of 1956-2002.During the past 135 years,21 extremely dry years and 19 extremely wet years occurred.These years represented 15.6% and 14.1% of the total study period,respectively.Six severe drought events lasting two years or more occurred in 1950-1951,1986-1987,1905-1909,1926-1928,1968-1969 and 1919-1920.Four wetter events occurred during 1954-1959,1932-1934,1939-1940 and 1990-1991.Comparisons with other tree-ring-based streamflow reconstructions or chronologies for surrounding areas supplied a high degree of confidence in our reconstruction.Power spectrum and wavelet analyses suggested that the reconstructed annual runoff variation in the Hulun Buir region and surrounding area could be associated with large-scale atmospheric-oceanic variability,such as the Pacific Decadal Oscillation(PDO) and El Ni o-Southern Oscillation(ENSO),and sunspot activity.     

Observation of mega-dune evaporation after various rain events in the hinterland of Badain Jaran Desert, China

The formation mechanisms of the mega-dunes and lakes in the hinterland of Badain Jaran Desert,China,is the focus of extensive academic research in the field of geoscience,and an often debated topic is whether atmospheric precipitation on the mega-dune can infiltrate to recharge groundwater.In the present study,the probability distribution functions and the return period analysis of extreme daily precipitation based on long-term precipitation records for the southern margin of Badain Jaran Desert and 2-year observation of hinterland precipitation were used to classify precipitation in the desert region.The data of automatic weather station and eddy covariance system in the desert hinterland were used to analyze evaporation on the mega-dune surface after various rain events.The results showed that the rain events in the desert could be divided into three categories.The first is conventional precipitation(CP),which is below 5 mm,accounting for roughly 90%of all rain events in the desert.The second and third categories are ordinary annual maximum(OAM)and extreme precipitation(EP),in which precipitation is roughly 20 mm and more than 40 mm,respectively.The atmospheric precipitation of CP and OAM evaporated from the megadune surface in 1–3 days and 3–4 weeks,respectively.Following an EP event,the mega-dune evaporation was negatively influenced by the upper dry sand layer,and a lengthy period was required for its complete removal.The accumulative evaporation and accumulative precipitation of all three types of rain events indicated that local atmospheric precipitation had no significant contribution to recharging the groundwater system in the hinterland of Badain Jaran Desert.This research will benefit comprehensive elucidation of the formation mechanism of lakes in the hinterland of Badain Jaran Desert.     

Variations of the spring precipitation day numbers reconstructed from tree rings in the Urumqi River drainage,Tianshan Mts. over the last 370 years

The tree-ring cores of Tianshan spruces col-lected from nine sites in the Urumqi River drainage of the middle Tianshan Mountains were used to establish three types of the tree-ring width chronologies over the last 370 years, using the international standard method of dendro-chronology. Our study demonstrates that dendrochronologycan be better used to reconstruct the number of the precipi-tation day than to reconstruct the precipitation amount in middle Tianshan Mountains. It is found that the residual chronology among the three tree-ring width chronologies has the best relationship with number of spring precipitation days from May 20 to June 8. The chronologies at Haxiong-gou B site and Zaierdegou site in the Urumiqi drainage have the highest correlation with the observed number of spring precipitation days at Daxigou meteorological station, and are used to reconstruct the spring precipitation days over the last 370 years in the drainage. The main significant decreasing trend of the number of the spring precipitation days oc-curred during 1665--1717, while the significant increasing trends happened during 1805--1841 and 1914--1943. The reconstructed series of the number of spring precipitation days has quasi-periodic variations of 3.3, 2.1, 2.5, 12.3 and 32.0 years with the dominated short periodical changes. The long cycle of 32 years is shown quite clearly in the 10-year smoothed sequence. The maximum spring precipitation days occurred mainly in the 1630s, 1840s and 1940s, while the lowest number of spring precipitation days for the 10-year average occurred in the 1710s.     

Landscape evolution and precipitation changes in the Badain Jaran Desert during the last 30 000 years

On the basis of field expeditions into different parts of the Badain Jaran Desert, new evidence of landscape evolution and precipitation changes during the last 30 000 years has been found from the geomorphological, sedimentological and geochronological studies of the megadune. Different cemented surfaces of palaeo-dunes have been observed in many localities, which are representatives of relatively moister environment. The chronological data show that four periods of more humid environment occurred in the past 30 000 years. The stabilization of dunes in a large scale and the existence of many palaeo-lakes and lacustrine terraces confirm the periodic fluctuations of climate. It implies that the intensity of westerlies and Eastasian monsoons varied in the region of Alashan, and the periods of higher precipitation took place even in the times close to the last glacial maximum.     

A 1000-year chironomid-based salinity reconstruction from varved sediments of Sugan Lake, Qaidam Basin, arid Northwest China, and its palaeoclimatic significance

A 1000-year high-resolution （-10 years） chironomid record from varved sediments of Sugan Lake, Qaidam Basin on the northern Tibetan Plateau, is presented. The chironomid assemblages are mainly composed of the relatively high-saline-water taxa Psectrocladius barbimanus-type and Orthocladius/ Cricotopus, and the relatively low-saline-water taxa Procladius and Psectrocladius sordidellus-type. Variations in the chironomid fauna and inferred salinities suggest that over the last millennium, the Sugan Lake catchment has alternated between contrasting climatic conditions, having a dry climate during the period 990-1550 AD, a relatively humid climate during the Little Ice Age （LIA） （1550-1840 AD）, and a dry climate again from 1840 AD onwards. At the decadal to centennial scale, a wet event around 1200-1230 AD, interrupting the generally arid period （990-1550 AD）, and a dry event around 1590-1700 AD, punctuating the generally humid period （1550-1840 AD）, are clearly documented. Trends in the chironomid-based salinity time series indicate a highly unstable climate during the LIA when salinity fluctuations were of greater magnitude and higher frequency. The effective moisture evolution in the Sugan Lake catchment during the last millennium reconstructed by chironomid analysis is in broad agreement with previous palaeo-moisture data derived from other sites in arid Northwest China （ANC）. The LIA, characterized by generally humid conditions over the westerly-dominated ANC was distinctly different from that in monsoonal China, implying an ＂out-of-phase＂ relationship between moisture evolution in these two regions during the past 1000 years.     

Landscape evolution and palaeoclimate in the deserts of northwestern China, with a special reference to Badain Jaran and Taklamakan

A comparative study of geomorphologic landscapes in the Badain Jaran Desert and Taklamakan Desert was made on the basis of field investigations, thermolumi-niscence and radiocarbon dating as well as analysis of sand grain texture. The sand seas of the Badain Jaran Desert differ greatly from that of the Taklamakan Desert in terms of dune morphology, interdune relief, dune stratigraphy and sand sources. The thermoluminiscence ages of the dunes suggest that the basic configuration of the megadunes in the Badain Jaran Desert has not changed at least since Middle Holocene. There were periods of more humid environment during the last glaciation and Holocene in both deserts, but events of higher precipitation in the Badain Jaran Desert were more frequent than in the Taklamakan. In both desert areas, aeolian processes have been intensified during the last 2000 a.     

Late Glacial and Holocene vegetation history and paleoclimate of the Tengger Desert,northwestern China

With a total area of 36000 km2, the Tengger Desert is the fourth largest desert in China. The Qilian Mountains demarcate the southwestern boundary of the desert andthe Helan Mountain on the east separates the desert from the Mo Us Desert. The Yabulai Mountain on thenorthwest borders the Tengger Desert and the BadainJaran Desert and the Loess Plateau touch its southern tip (Fig. 1). Climatically, the area is situated at the junction of the hyper-arid northwest, the arid to semi-arid sou…     

Precipitation variations recorded in Guliya ice core in the past 400 years

Based on the Guliya ice core records, the precipitation in the past 400 years was retrieved. Its rela tions with other regions were also analyzed. The results demonstrated that there were two high-precipitation periods and two low-precipitation periods in Guliya ice core since 1571 AD. The average precipitation in the two high-precipitation periods was 42 mm (21%) higher than that in the two low-precipitation periods. The precipitation recorded in the Guliya ice core was consistent with that in Dunde ice core. The variation trends of precipitation in the Guliya ice core and the northern hemisphere are similar. During the extremely wet years in the northern hemisphere, the precipitation recorded in the Guliya ice core was two times the long-term average. However, the annual precipitation was 38% less than that of the long-term average in extremely dry years.     

Precipitation variations recorded in Guliya ice core in the past 400 years

Based on the Guliya ice core records, the precipitation in the past 400 years was retrieved. Its rela tions with other regions were also analyzed. The results demonstrated that there were two high-precipitation periods and two low-precipitation periods in Guliya ice core since 1571 AD. The average precipitation in the two high-precipitation periods was 42 mm (21%) higher than that in the two low-precipitation periods. The precipitation recorded in the Guliya ice core was consistent with that in Dunde ice core. The variation trends of precipitation in the Guliya ice core and the northern hemisphere are similar. During the extremely wet years in the northern hemisphere, the precipitation recorded in the Guliya ice core was two times the long-term average. However, the annual precipitation was 38% less than that of the long-term average in extremely dry years.     

中国历史气候记录揭示的千年干湿变化和重大干旱事件

对中国历史气候记录的研究表明：准周期性是过去1000年间中国东部各区域的干湿气候变化的基本特征；各区域间主要周期变化的位相差异，表现为降水的空间分布格局（如南涝北旱、北涝南旱等分布型）随时间的变化；1000年来干湿气候发生过多次十年和百年尺度的突变，降水的突变对农业生产会有明显影响。过去1000年间多次出现过大范围的持续时间3年以上的严重于旱事件，其严重程度多为最近50年所未见，因此，在过去1000年的气候变化历程中，最近的50年沿属于气候条件较好 的时段，但对未来出现气候突变和重大气候灾异的可能性应予以警惕。     

Palaeolake and palaeoenvironment between 42 and 18 kaBP in tengger desert, NW China

Comprehensive field investigations and laboratory analyses show that palaeolakes, including fresh- mesohaline water Megalake Tengger and other semi-con- nected, isolated water bodies, during late Pleistocene covered an area of more than 20000 km², which is more than half of the Tengger Desert in NW China. Stratigraphic correlation and chronological evidence indicate that before ca. 42000 aBP the area was more arid. The palaeolakes started to develop around 40000 uncal. ¹⁴C aBP but until 37000 ¹⁴C aBP their scope was limited. High water levels established from 35000 ¹⁴C aBP lasted until 22000 ¹⁴CaBP. Lake levels regressed between 22000 and 20000 ¹⁴C aBP but transgressed from 20000 to 18600 ¹⁴C aBP. Subsequently, water level declined further and the Megalake Tengger finally desiccated at around 18000 ¹⁴C aBP. Megalake Tengger possessed a fresh-mesohaline water property, implying that the regional precipitation increased significantly. During the period of Megalake Tengger, the climate was warmer-humid than present. The annual rainfall was 250 to 350 mm more than that of today and the temperature was 1.5 to 3.0℃ higher.     

天山北麓500年来环境演变及其对人类活动的影响

文章在分析前人研究成果的基础上,总结归纳出天山北麓500年来温度、湿度以及温湿组合演变的基本规律,500年来天山北麓地区的环境演变大致经历了三个冷暖期以及四个湿润期和三个干旱期的交替,主要以冷湿、暖干的气候类型交替出现.在此基础上,笔者探讨了气候变化对干旱地区绿洲生态系统的稳定、灌溉农业的发展,水资源和环境以及灾害及其防治等方面的影响,认为气候变化有利于该地区水资源的利用,但也给部分地区带来了比较严重的洪涝灾害.     

云南省雨季降水量变化的区域特征分析

 用EOF,REOF方法对1961～2002年云南省124个测站雨季降水的时空分布、演变规律及各区域的降水特征进行了诊断分析.结果表明:大范围区域降水的一致性是云南雨季降水的主要特征,其次为东、西反向变化以及东南、东北反向变化空间异常分布型态;云南雨季降水存在着7个主要的异常区域:滇中以东区,滇南区,滇西北区,滇中以西区,滇西南区,滇东南区,滇东北区;除滇东南区之外,其他各区在20世纪90年代末期雨季降水都有增多的趋势.     

High－resolution precipitation variations in the Northeast Tibetan Plateau over the last 800 years documented by sediment cores of Qinghai Lake

Short cores of about 80-cm retrieved from three main basins of th e deepwater areas in Qinghai Lake,the largest inland enclosed lake in China, were studied. Sta-ble isotopes of authigenlc carbonates, grain-size, carbonate and organic matter content at 5-year resolution are used to reconstruct the climatic history over the last 800 years in the Northeastern Tibetan Plateau. Chronology was established according to 210^pb dating and 137^Cs methods and the core corrdation. It is found that cores from different deep basins of the lake can be well correlated. The sedimentary rate is highest in the western basin of the lake and lowest in the east.In the southern basin of the lake where the short core Qing-6is located, the recent average sedimentation rate is 0.1004cm/yr. Variations in effective precipitation recorded by the oxygen isotopes and grain size data durine the last 800 years are consistent with the glacial accumulation record form the Dunde and Guliya ice cores. A dry climate lasted for 300 years from 1200 AD to 1500 AD, followed by a wet period from 1500 to 1560 AD. The two dry periods, 1560 to 1650 AD and 1780 to 1850 AD, were the results of southwest monsoon weakening. The effective precipitation generally increased since 1650 AD due to the strengthening of the Asian South-west Monsoon, resulting in a wet period until the 1950s. Ex-cept the early stage, the Little Ice Age on the Plateau is characterized b y increased effective moisture. Organic mat-ter content, with nearly 200-year cycles, shows similar trend with the atmospheric delta earbon-14 before the 1850s, indi-eating that the bioproductivity responds to solar activity.     

晋南地区近50年来气温与降水量变化趋势分析

利用隰县、临汾、运城3个地面气象站1961年-2010年的气温和降水量资料,研究了晋南地区近50年来气温与降水量的变化趋势．研究表明,晋南地区1961年～2010年间年均气温呈上升趋势,增温速率为0．35℃／IOa,高于山西省和全国气温平均增长率,并且年均气温的上升主要源于冬春季节的快速升温．同时,该区60年代和70年代为相对寒冷期,80年代为相对平稳期,而90年代和本世纪前十年为相对温暖期,特别是本世纪前十年增温趋势十分明显．晋南地区近50年来年平均降水量以18．3mm／lOa的速率减少,并且夏秋季节对年降水量减少的贡献最大．该区60年代和70年代为相对多雨期,而90年代和本世纪前十年则为相对少雨期,特别是90年代,降水减少的幅度更明显．     

A mid－Holocene drought interval as evidenced by lake desiccation in the Alashan Plateau,Inner Mongolia,China

The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong sum-mer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lakegeomorphologic and lithologicai evidence from the Alashan Plateau, part of the Mongolian Plateau, that indicates stronglake desiccation during the mid-Holocene. High resolution pollen data from Zhuyeze Lake, at the present summermonsoon margin, is also presented. These data show that present lakes and wetlands in the Juyanze Lake basin west of the Badain Jaran desert, in the Zhuyeze Lake basin between the Badain Jaran and Tengger deserts, and in lakes in the eastern Tengger desert, dried or experienced low lake levelsin the mid-Holocene around 5000-7000 cal yr BP. Pollen data further indicate that the vegetation cover declined in both the local areas and in the Qilian Mountains, suggesting the climate was drier than that associated with the presentAsian summer monsoon. This mid-Holocene drought interval was present throughout a quite large region of the south In-ner Mongolian Plateau. The period was also probably colder,at least in the high Asian plateaus and mountains.