气温升高对黄土高原半干旱区陆面特征影响的数值模拟

利用中尺度数值模式MM5,设计控制试验及敏感性试验,模拟分析气温升高对黄土高原半干旱区陆面特征的影响状况。结果表明:气温升高后,该地区地-气温差基本上是减小的;土壤表层温度受影响较大,深层受影响较小;感热、潜热通量及地表热通量均是减小的;长波辐射受影响较复杂,短波辐射基本是减少的;边界层高度白天降低,减小了昼夜高度差,进而减小了该层能量传输与转换。总体来讲,气温升高使边界层能量传输减小。     

内蒙古农牧交错带中部地区荒漠化与土地利用之关系分析

本文利用RS与GIS技术手段分析了内蒙古农牧交错带中部地区荒漠化情况,得 出结论如下:①研究区土地退化主要以草地、耕地退化为主。其中,草地退化严重。在2000 年,草地退化面积达3556516.9hm2,占总草地面积的75.3%;耕地退化面积为1905119.6 hm2,占总耕地面积的69.2%。②研究区土地荒漠化面积达5982412.2hm2,占研究区面积的 71.0%。其中风蚀荒漠化面积最大,占研究区总面积的38.6%;水蚀荒漠化面积次之,面积 2491597hm2,占研究区总面积的29.6%;盐渍化面积最小,为239296hm2,只占2.8%。     

讨赖河流域近30年土地利用与景观格局动态

以讨赖河流域1976年Landsat MSS、1989年、2000年和2010年的Landsat TM 4期遥感影像为数据源,运用土地利用变化幅度、动态度、转移矩阵等方法,并结合景观指数,采用主成分分析方法,分析了流域1976-2010年间的土地利用/覆被和景观格局的变化及其驱动力。结果表明：近34年,研究区耕地和城乡建设用地所占比例持续上升,分别由4％和0．04％增加到7．4％和0．26％;冰川和永久性积雪、草地面积则分别减少897．98 km2和383．69 km2。各土地利用类型中以城乡建设用地的动态度最高,达16．13％,耕地次之。土地利用类型间主要转移方向为：冰川和永久性积雪转化为裸岩石砾地,戈壁转化为耕地,林地与草地间相互转化。整个景观的斑块密度先增大后降低,最大斑块指数先减小后增大,景观趋于更加破碎,景观的多样性先减小,后增加。人口增长和经济发展因素是研究区土地利用/覆被变化的最直接驱动力,同时也受气候因素的影响。     

河西绿洲对祁连山区环境影响的数值模拟

利用中尺度模式MM5V3.7,设计了河西绿洲对祁连山区环境影响的控制试验和河西绿洲退化为沙漠稀疏植被的敏感性试验,数值模拟结果表明:河西绿洲的退化对祁连山区环境有较大的影响,绿洲退化之后激发出一个局地热力环流,使得祁连山区的谷风增大,气温升高,湿度减小,这种热力作用可以到达高空550hPa左右;绿洲的退化对局地环境也会产生较大的影响,如局地气温升高,湿度减小,感热通量增大,潜热通量减小。     

黄河源区高寒草地不同深度土壤理化性质与抗剪强度关系研究

以黄河源区的高寒草地为研究对象,探讨了草地和裸地在0～10 cm、10～20 cm、20～30 cm、30～40 cm和40～50 cm 5种不同深度土壤理化性质和根-土复合体抗剪强度特征.研究结果表明:黄河源区的土壤为弱碱性土,且pH值、密度随着土壤深度增加而增大.土壤含水率、有机质随土壤深度的增加表现出减小的变化趋...     

黄河源区玛曲3次积雪过程能量平衡特征

利用中国科学院黄河源区气候与环境综合观测研究站2011年12月至2012年3月的观测资料,对比分析了黄河源区玛曲3次积雪过程地表辐射和能量平衡特征,结果表明:受雪面较大反照率的影响,降雪后净辐射减小显著,3次降雪前、后净辐射分别为154、200、210 W·m~(-2)和93、129、130 W·m~(-2)。3次降雪后及融雪后,地—气能量交换受天气条件和土壤冻融状态的影响较大:第1次降雪后较低的气温和地表温度并没有影响冻结土壤原本就较弱的蒸发能力,潜热通量在降雪前、后及融雪后量值较小且相差不大;第2次降雪后的2月18日,较大的风速(≥4 m·s~(-1))和较强的太阳辐射加快了积雪的升华,潜热通量量值较大,日均值高达118 W·m~(-2),风速与潜热通量同步变化,且峰值同时出现(分别为15 m·s~(-1)和300 W·m~(-2)),积雪升华消耗能量使地表温度降低并低于气温,出现负感热通量,日均值为-8 W·m~(-2),峰值达-40 W·m~(-2),融雪后感、潜热通量很快达到降雪前的水平;第3次降雪后的2月29日至3月3日,浅层土壤温度由-1℃逐渐上升并维持在冻土可融化温度-0.18℃左右,冻土壤融化吸收热量,潜热通量与降雪前相比增加不明显,3月4日是积雪融化的最后一天,较湿的土壤和融雪水蒸发释放潜热,潜热通量较3月3日显著增大;积雪融化后,潜热通量受浅层土壤蒸发能力增强的影响较降雪前明显增大。     

天山科其喀尔冰川区复杂下垫面CO_2通量贡献区分析

大气湍流交换过程中CO_2有效源(汇)区域即CO_2通量贡献区,在冰川作用区不仅受到水化学侵蚀强度的影响,还受区域微气候的影响,另外,动态的下垫面和复杂地形也增加了实际监测的不确定性。为了评估冰川区CO_2通量监测结果的空间代表性,在西天山南坡科其喀尔冰川表碛区利用涡度协方差观测系统进行观测,同时,结合基于KM足迹模型基础上开发的ART Footprint Tool足迹软件对通量贡献区进行分析,结果表明:(1)积雪积累期主风向以NW为主,风向频率占53.31%;积雪消融期和冰川消融初期NW向主风减少,偏北的NNW风逐渐增多,但冰川消融峰期后又逐渐过渡为NW风向。(2)积雪积累期雪冰融水几乎消失,但大气CO_2通量平均为-0.07 g·m~(-2)·d~(-1),尤其是白天为-0.88 g·m~(-2)·d~(-1),仍呈没收现象,是由于白天较强辐射下,少量积雪融水引起可溶性物质淋溶过程中水化学反应没收大气CO_2所致;而夜间冰川消融峰期CO_2通量值平均为0.33 g·m~(-2)·d~(-1),呈释放CO_2现象,这可能与夜间区域降温及降水过程中溶解的CO_2因地表蒸发返回大气所致。(3)通量贡献率80%以上的各期0.5 h数据占比依次为:积雪积累期(95.80%)积雪消融期(93.28%)冰川消融峰期(86.13%)冰川消融初期(81.88%),而足迹最远点分布距离顺序与前者几乎相反,但均分布在主风向下的冰川中流线上,说明对CO_2通量监测值有显著影响的贡献区比较集中,也意味着冰川末端及两侧山脊草地CO_2通量变化的影响可以忽略。(4)白天在大气稳态条件下,贡献区解释的CO_2通量为(78.55±2.08)%,略高于夜间的(77.72±1.41)%,但显著低于非稳定条件下白天(89.86±0.22)%和夜间(89.45±0.57)%的解释结果,进一步验证了CO_2通量贡献区比较集中。     

近50a西北干旱区气候变化趋势及对荒漠化的影响

西北干旱区干旱少雨,生态环境脆弱,土地荒漠化严重。本文根据近1951-2000年的逐月平均气温和月降水量资料研究了我国西北干旱区气候变化趋势,并结合近年来西北干旱区地表径流量变化,分析其对准噶尔盆地、塔里木盆地、河西走廊和柴达木盆地土地荒漠化影响。研究结果表明:(1)近50a西北干旱区气温都升高,变暖最显著的是北疆和柴达木盆地。降水量有增加趋势,其中南疆降水量增加趋势最大。北疆蒸发量有减少趋势外,其他区蒸发量都在增加,尤其南疆蒸发量增加趋势最大。(2)近50a来由于气候变暖,使蒸发量增大,塔克拉马干沙漠、河西走廊沙漠区和柴达木沙漠区的干旱危害加剧,这必然导致沙漠化的易发和其进程的加速。北疆气温升高,降水量增加,而蒸发量减少,有利于古尔班通古特沙漠区沙漠化进程的减缓。(3)气候变化和地表径流量变化有利于准噶尔盆地和塔里木盆地的土地荒漠化逆转,而使河西走廊和柴达木盆地的土地荒漠化发展迅速。     

近40年玛曲草地暖干化趋势及影响因子分析

通过利用Holdridge可能蒸散率(PER),对玛曲草地1971～2010年的干湿变化特征进行了分析,近40年玛曲草地PER呈明显的上升趋势,上升趋势达0.03/10a,20世纪90年代后,玛曲草地PER持续偏高,并在1993年出现了增大突变,降水量以7.4mm/10a的趋势减少,温度以0.46℃/10a的趋势上升,生物温度以0.25℃/10a的趋势上升,降水量与生物温度呈现出明显反向变化,玛曲草地有从极湿润区向湿润区过渡的趋势,出现了明显的暖干化趋势。主成分分析表明玛曲草地暖干化的主要原因是气温升高,同时日照时数增加、降水量减少、相对湿度下降和风速减小加剧了暖干化的趋势。受气候暖干化和人为因素的影响,玛曲草地出现了明显的退化和沙化,沼泽湿地的面积也呈明显的减少趋势,导致玛曲草地牧草产量下降,涵养水源能力急剧下降和生物多样性锐减。     

近20 a塔里木河干流区土地利用变化特征

基于GIS技术及景观生态学原理,利用塔里木河干流区4期（1990年、2000年、2005年和2008年）土地利用遥感影像解译数据,研究近20 a塔里木河干流区土地利用的变化特征。结果表明：塔里木河治理后的10 a干流耕地面积增加了1.03×10⁵ hm²,耕地动态度增加较大,盐碱地面积增加了7.13×10⁴ hm²,较治理前增速呈减缓态势;草地面积约减小了4.91×10⁵ hm²,林地、水域面积呈先增加后减小的趋势,但两者动态度减小。沙地、盐碱地的动态度减小,表明塔里木河综合治理基本抑制了干流区盐碱地、沙地面积增加的速度。同时,土地利用类型转移的方向主要是草地、林地、耕地、沙地之间的相互转化。塔里木河综合治理引起干流区水资源的再分配,对耕地、林地和盐碱地面积的变化影响较大;从各景观类型指标分析,聚集度指数明显降低,说明景观破碎度和连通性降低;而多样性指数和均匀度指数增加,表明区域景观异质性增加,稳定性增大。这些变化可能导致土壤表层积盐,沼泽地面积减少。本研究将有助于对综合治理工程的实施效果进行综合评估。     

基于MODIS数据的中国热环境时空变化研究

以2011年1、4、7、10月份的MODIS陆地表面温度产品(MOD11A2)、地表覆盖类型产品(MOD12Q1)为依据,采用GIS的空间分析,方差分析和统计分析方法,研究了中国陆地表面温度(LST)的季节变化规律,以及LST与不同下垫面类型之间的相互关系。结果表明:(1)冬季,整个区域昼夜呈现出陆地表面温度随纬度递减而逐渐上升的趋势;夏季白天,北方大部分地区陆地表面温度要比东南沿海地区高,晚上,则相反。(2)不同下垫面类型对陆地表面温度的影响较为显著,整体表现为,白天,林地、草地、水体、耕地、未利用土地、建设用地的陆地表面温度依次升高;黑夜,水体、林地、草地、耕地、建设用地、未利用土地的陆地表面温度依次降低。这种变化趋势和下垫面类型的热容量性质具有密切的关系。     

Effects of long-term warming on the aboveground biomass and species diversity in an alpine meadow on the Qinghai-Tibetan Plateau of China

Ecosystems in high-altitude regions are more sensitive and respond more rapidly than other ecosystems to global climate warming.The Qinghai-Tibet Plateau(QTP)of China is an ecologically fragile zone that is sensitive to global climate warming.It is of great importance to study the changes in aboveground biomass and species diversity of alpine meadows on the QTP under predicted future climate warming.In this study,we selected an alpine meadow on the QTP as the study object and used infrared radiators as the warming device for a simulation experiment over eight years(2011-2018).We then analyzed the dynamic changes in aboveground biomass and species diversity of the alpine meadow at different time scales,including an early stage of warming(2011-2013)and a late stage of warming(2016-2018),in order to explore the response of alpine meadows to short-term(three years)and long-term warming(eight years).The results showed that the short-term warming increased air temperature by 0.31℃and decreased relative humidity by 2.54%,resulting in the air being warmer and drier.The long-term warming increased air temperature and relative humidity by 0.19℃and 1.47%,respectively,and the air tended to be warmer and wetter.The short-term warming increased soil temperature by 2.44℃and decreased soil moisture by 12.47%,whereas the long-term warming increased soil temperature by 1.76℃and decreased soil moisture by 9.90%.This caused the shallow soil layer to become warmer and drier under both short-term and long-term warming.Furthermore,the degree of soil drought was alleviated with increased warming duration.Under the long-term warming,the importance value and aboveground biomass of plants in different families changed.The importance values of grasses and sedges decreased by 47.56%and 3.67%,respectively,while the importance value of weeds increased by 1.37%.Aboveground biomass of grasses decreased by 36.55%,while those of sedges and weeds increased by 8.09%and 15.24%,respectively.The increase in temperature had a non-significant effect on species diversity.The species diversity indices increased at the early stage of warming and decreased at the late stage of warming,but none of them reached significant levels(P>0.05).Species diversity had no significant correlation with soil temperature and soil moisture under both short-term and long-term warming.Soil temperature and aboveground biomass were positively correlated in the control plots(P=0.014),but negatively correlated under the long-term warming(P=0.013).Therefore,eight years of warming aggravated drought in the shallow soil layer,which is beneficial for the growth of weeds but not for the growth of grasses.Warming changed the structure of alpine meadow communities and had a certain impact on the community species diversity.Our studies have great significance for the protection and effective utilization of alpine vegetation,as well as for the prevention of grassland degradation or desertification in high-altitude regions.     

Vertical distribution of sand-dust aerosols and the relationships with atmospheric environment

The vertical distribution of aerosols in the troposphere is important for determining their effects on climate.The vertical distribution of aerosols under different atmospheric conditions in the free troposphere was directly observed using a surface micro-pulse LIDAR(MPL) and a TP/WVP-3000 microwave radiometer at the Semi-Arid Climate & Environment Observatory of Lanzhou University(SACOL,35.95°N,104.10°E) in the western Loess Plateau,China,in the spring of 2008.The results showed two possible transportation paths of a sandstorm from May 1 to May 4 in 2008.In one path,sand-dust aerosols were transported toward the east from the Taklimakan Desert to the Badain Jaran Desert and the Tengger Desert by a westerly wind and then toward the southeast to Jingtai and Lanzhou.A weak aerosol index(AI) indicated another possible transport path toward the east from the Taklimakan Desert to the Qaidam Basin and through the Tibetan Plateau eastward to SACOL.The aerosol profile of sandstorm processes over the SACOL area displayed three patterns:a single peak distribution under stable atmospheric conditions,indicating urban aerosol distribution;an exponential decrease under unstable atmospheric conditions in the presence of a sandstorm;and a slight change in the mixed layer during the first and last stages of the sandstorm,indicative of thorough mixing during lifting and deposition stages.Analyses of the aerosol layer height(ALH) showed that there are two types of ALH diurnal variation.The ALH during the first sandstorm stage was complex and disordered,and affected by atmospheric circulation.While the ALH had obvious diurnal variation in the other stage,the ALH and aerosol extinction coefficient(AEC) had a single peak,and was higher in the afternoon and lower in the morning.In the second case the ALH was in agreement with the atmospheric boundary layer height(BLH) variation.As a result of the development of the atmospheric boundary layer(ABL) during day and maintenance at night,ALH during sandstorm-free days showed obvious diurnal variations.Multiple vertical distribution patterns of sand-dust aerosols will result in different climate effects;therefore,the vertical distribution patterns can be used to parameterize climate and aerosol models.     

南疆沙漠腹地地温变化特征

利用塔中气象站三年的气象数据,分析了塔中地温的变化特征。结果显示:塔中0～40cm地温年变化规律显著,温度自1月开始迅速上升,在7月达到最高值,达30℃以上,其后又持续下降,冬季最低;80cm以下地温变化平缓,最高、最低温度出现月份逐渐后延,年振幅渐小;在典型晴天、阴天、沙尘天气时,表层地温都是日出前后最低,日出后迅速上升,至午后16时左右达最大值,其后迅速下降,于日落时降至一低值,并在夜间继续缓慢下降;四季0～80cm各层地温夏季﹥秋季﹥春季﹥冬季;天气对地温的影响主要体现在地表温度和浅层地温,至40cm及以下各层几乎无影响,日变化与典型晴天规律相同;阴天和浮尘对地温的影响较小,扬沙和沙尘暴天气对地温影响较大,其影响随深度增加而渐小;各层地温的平均日变化曲线近于正弦曲线,随深度增加地温特征线趋于平缓,极值出现时间逐渐后延。塔中地温的年际、日内变化的逐层性,与沙漠表面风成沙的物理属性有关。     

New evidence for the links between the local water cycle and the underground wet sand layer of a mega-dune in the Badain Jaran Desert,China

Scientists and the local government have great concerns about the climate change and water resources in the Badain Jaran Desert of western China. A field study for the local water cycle of a lake-desert system was conducted near the Noertu Lake in the Badain Jaran Desert from 21 June to 26 August 2008. An underground wet sand layer was observed at a depth of 20–50 cm through analysis of datasets collected during the field experiment. Measurements unveiled that the near surface air humidity increased in the nighttime. The sensible and latent heat fluxes were equivalent at a site about 50 m away from the Noertu Lake during the daytime, with mean values of 134.4 and 105.9 W/m2 respectively. The sensible heat flux was dominant at a site about 500 m away from the Noertu Lake, with a mean of 187.7 W/m2, and a mean latent heat flux of only 26.7 W/m2. There were no apparent differences for the land surface energy budget at the two sites during the night time. The latent heat flux was always negative with a mean value of –12.7 W/m2, and the sensible heat flux was either positive or negative with a mean value of 5.10 W/m2. A portion of the local precipitation was evaporated into the air and the top-layer of sand dried quickly after every rainfall event, while another portion seeped deep and was trapped by the underground wet sand layer, and supplied water for surface psammophyte growth. With an increase of air humidity and the occurrence of negative latent heat flux or water vapor condensation around the Noertu Lake during the nighttime, we postulated that the vapor was transported and condensed at the lakeward sand surface, and provided supplemental underground sand pore water. There were links between the local water cycle, underground wet sand layer, psammophyte growth and landscape evolution of the mega-dunes surrounding the lakes in the Badain Jaran Desert of western China.     

冷锋天气过程大气边界层特征与颗粒物污染

利用兰州大学半干旱气候与环境观测站边界层铁塔梯度观测、湍流观测和PM₁₀浓度资料,分析一次典型冷锋天气过程兰州大气边界层结构和湍流输送特征及其与PM₁₀浓度的关系。结果表明：冷锋过境前边界层有逆温层出现。随着锋面过境,逆温层完全被破坏、消失,混合层迅速发展,边界层低层温度和湿度垂直梯度变得很小,风速垂直梯度则明显增大;PM₁₀浓度先升后降。冷锋过境时垂直湍流输送强烈,经向和纬向动量均向下输送。动量下传使地表尘沙大量扬起,造成冷锋过境初期颗粒物浓度骤升。     

生态脆弱区土地利用变化与沙漠化响应研究——以宁夏中部干旱带为例

以宁夏中部干旱带1978年MSS及1987、1996和2007年Landsat TM/ETM遥感影像为信息源,在3S技术支持下,对不同时期土地利用与沙漠化与沙漠化变化响应关系进行了分析。结果表明：耕地和草地是该地区的主要土地利用类型,分别占总面积的27.7%,24.7%。近30a来,耕地、城镇用地面积增幅较大,分别增加...     

河北省近50年农业界限温度变化特征分析

利用京、津、冀区域内196l～200r7年70个气象观测站点系统的气象观测资料,对河北省≥0℃、10℃界限温度的初日、终日、初终间日数、积温的空间变化、年际变化、年代际变化进行了分析.结果表明:近50年来,全省及各区域≥0℃、10℃界限温度总的变化趋势表现为,初日提前、终日推迟、初终间日数延长、积温增加.20世纪70年...     

Summer atmospheric boundary layer structure in the hinterland of Taklimakan Desert,China

Understanding the characteristics of the structure of desert atmospheric boundary layer and its land surface process is of great importance to the simulations of regional weather and climate.To investigate the atmospheric boundary layer structure and its forming mechanism of Taklimakan Desert,and to improve the accuracy and precision of regional weather and climate simulations,we carried out a GPS radiosonde observation experiment in the hinterland of Taklimakan Desert from 25 June to 3 July,2015.Utilizing the densely observed sounding data,we analyzed the vertical structures of daytime convective boundary layer and nighttime stable boundary layer in summer over this region,and also discussed the impacts of sand-dust and precipitation events on the desert atmospheric boundary layer structure.In summer,the convective boundary layer in the hinterland of Taklimakan Desert developed profoundly and its maximum height could achieve 4,000 m;the stable boundary layer at nighttime was about 400–800-m thick and the residual mixing layer above it could achieve a thickness over 3,000 m.Sand-dust weather would damage the structures of nighttime stable boundary layer and daytime convective boundary layer,and the dust particle swarm can weak the solar radiation absorbed by the ground surface and further restrain the strong development of convective boundary layer in the daytime.Severe convective precipitation process can change the heat from the ground surface to the atmosphere in a very short time,and similarly can damage the structure of desert atmospheric boundary layer remarkably.Moreover,the height of atmospheric boundary layer was very low when raining.Our study verified the phenomenon that the atmospheric boundary layer with supernormal thickness exists over Taklimakan Desert in summer,which could provide a reference and scientific bases for the regional numerical models to better represent the desert atmospheric boundary layer structure.