The effect of hydrologic process changes on NDVI in the desert-oasis ecotone of the Hexi Corridor     

ZHAO WenZhi  CHANG XueLi 《中国科学:地球科学(英文版)》2014,(12)

In the arid inland river basins of northwestern China,human activities control almost all the surface hydrologic processes.The potential effects of these altered hydrologic processes are gradually becoming clear,especially since the 2000 implementation of the integrated water resources management projects in the Shiyang River,the Heihe River,the Tarim River,and the Shuler River.While the appearance of these eco-hydrology changes and consequent environmental effects in the oasis has attracted broad attention,related research is still lacking.Eco-hydrological process changes in the desert-oasis ecotone were investigated in the Pingchuan irrigation district in the middle reaches of the Heihe River.The results showed that the annual average amount of surface water irrigation during the past 20 years has decreased by 1.498×107 m3,while the annual average amount of well irrigation has increased by 1.457×107 m3,since 2000,when the State Council of China approved the water diversion scheme for the Heihe River Basin.The groundwater depth before the water diversion scheme generally varied between2.44–3.19 m(average 2.73±0.24 m),while that after the water diversion scheme has varied between 3.08–4.01 m(average3.79±0.62 m).The distribution area of3 m groundwater depth decreased from 3612 to 394 hm2;while the distribution area of3 m groundwater depth increased from 853 to 3843 hm2.However,although the hydrologic processes changed dramatically,no significant effects on vegetation productivity in the desert-oasis ecotone were detected during the study period.  相似文献   

黄河内蒙古段支流“十大孔兑”侵蚀产沙的时空变化及其成因   总被引：2，自引：2，他引：0  

许炯心 《中国沙漠》2014,34(6):1641-1649

“十大孔兑”来沙造成黄河干流强烈淤积.为了通过流域治理来减轻泥沙灾害,研究“十大孔兑”侵蚀产沙过程具有重要意义.基于1960—2005年的河流输沙量、径流量和降雨量资料,运用统计方法进行了研究.结果表明:“十大孔兑”输沙量高度集中于几个大水大沙年份,其余年份对46年总输沙量的贡献很小.最大1年、最大3年、最大5年和最大10年的累积输沙量分别占到46年总输沙量的21.26%、37.18%、47.92%和69.29%.1960—1991年和1992—2005年两个时段相比,后一时段输沙量年均值减少了37%.这一差异可以用暴雨特征的差异和下垫面(如植被)的变化来解释.1991年以后,年降水量无明显变化,但最大1日降雨量在p<0.10的水平上呈现减小的趋势.虽然20世纪90年代西柳沟并未大规模实施水土保持治理,但由于农村富余劳动力转移,对土地的压力减轻,对植被的破坏大大减弱,使得植被逐渐恢复,NDVI呈增大趋势,因而侵蚀产沙减弱.“十大孔兑”产沙模数具有明显的空间分异特征,从西向东增大,在西柳沟达到最大值,然后再减小.流域自然地理因素具有明显的变化,从西向东,沙尘暴频率减小,降雨量增大.沙丘类型也发生了变化,由以流动沙丘为主变为以半固定沙丘为主,进入河道风沙的输沙强度减小.另一方面,水力驱动的侵蚀和泥沙输移从西向东增强.上述两种作用叠加的结果,在区域中部西柳沟附近出现了侵蚀产沙的峰值区.  相似文献   

长生命史飑线在强、弱对流降水过程中的异同点分析   总被引：5，自引：0，他引：5  

姚晨  郑媛媛  张雪晨 《高原气象》2012,31(5):1366-1375

利用常规气象资料、自动站资料、NCEP再分析资料和多普勒雷达资料,对发生在我国中纬度地区不同对流环境下两次长生命史飑线过程的物理机制和中尺度特征进行了分析。结果表明:(1)飑线在近地面层有较强的水汽辐合,但强对流降水过程中的飑线湿层深厚,水汽辐合的层次更为深广、强度更强,存在较低的抬升凝结高度。(2)高层强冷平流与低层暖平流的叠加是飑线的共同特征之一;不同之处在于弱对流降水过程中飑线不稳定层结的建立更多地依靠高层冷平流的作用,有更高的温度直减率,具有弱降水超级单体的一些特征;强对流降水过程中飑线低层暖平流的加强也是造成大气不稳定的重要原因,θse在中层呈现出湿中性层结特征,存在更大的热力不稳定度,是典型的强降水超级单体特性。(3)长生命史飑线的发展离不开强环境风垂直风切变;强对流降水过程中垂直风切变主要是风速随高度变化而产生的,弱对流降水过程中垂直风切变主要表现为风向随高度的变化。(4)飑线沿着出流边界和引导气流方向移动。(5)飑线在雷达回波上的共同点:都出现典型弓形回波,减弱的标志亦是阵风锋逐渐远离回波主体,弓形回波逐渐断裂,强回波后侧的层状云回波面积开始增大;不同点在于弓形回波的演变方式不同,弱对流降水过程中的弓形回波有超级单体风暴的典型结构,而强对流降水过程中弓形回波的形成是由强降水超级单体的发展而来,单体结构明显不同于经典超级单体中非降水或弱降水超级单体。(6)速度场上低层存在着径向速度的大值区,中低层有辐合,并伴有中气旋存在,中层存在明显的MARC(Mid-Altitude Radial Convergence)。1km高度以下的径向速度大值区、MARC和中气旋对地面灾害性大风有提前预警作用。  相似文献   

路面气象数值预报模型及性能检验          下载免费PDF全文

孟春雷  张朝林 《应用气象学报》2012,23(4):451-458

该文基于通用陆面模式 (CoLM) 发展了精细化路面参数数值预报模型 (BJ-ROME)。该模型可以预报路面温度、积雪厚度、积冰厚度以及积水厚度。模型不仅考虑了路面的不透水性、相对较低反照率、低热容以及高热导率等特征,还考虑了城市人为热的影响。模型采用北京市气象局快速更新循环预报系统 (BJ-RUC) 产生的气象强迫场驱动,预报时间跨度为24 h,更新时间为3 h。采用北京地区芬兰Vaisala公司路面观测站2009年8月9—24日路面温度及2010年1月3—4日积雪厚度观测结果对模型预报结果进行验证,同时进行了敏感性试验。结果表明:无论是在晴空还是降水的气象条件下,BJ-ROME均能较准确地预报路面温度极值以及日变化。BJ-ROME还可以较准确地模拟积雪厚度的最大值以及随时间变化情况。  相似文献   

最大熵增地表蒸散模型:原理及应用综述     

Wang Jingfeng  刘元波  张珂 《地球科学进展》2019,(6):596-605

精确估算地表蒸散一直是地球系统科学中的难点问题。经典的蒸散模型大多建立在水汽输送及能量平衡约束等基础上,相关的基础理论研究进展缓慢。最大熵增地表蒸散(E-MEP)模型是在综合借鉴贝叶斯概率论、信息熵概念、非平衡态热力学理论和大气边界层湍流相似性理论的基础上,建立的全新地表蒸散理论框架,克服了经典模型的主要缺陷,包括:离散梯度模型不满足能量守恒条件,Penman模型针对饱和土壤,Penman-Monteith模型需要率定经验参数等。E-MEP模型具有3个显著特点:①同时给出地表(包括水面、雪面和冰面)蒸散量、感热通量和介质表面热通量,且在所有时间空间尺度上满足能量平衡方程;②模型公式中没有可调经验参数,不依赖于温度梯度和水汽梯度变量,不需要输入风速和表面粗糙度;③适用于任何土壤含水量和植被覆盖条件。由于E-MEP模型建立在坚实的数学物理基础上,并具有解析表达式,简单易用,其输入变量和模型参数少于传统蒸散模型使用。地表辐射、表面温度、表面比湿等模型输入变量易于实地观测获取,且可通过遥感反演获得。检验分析表明,E-MEP模型优于Penman和Penman-Monteith等传统蒸散模型。这一全新的地表蒸散模型已被用于大尺度地表水热的遥感反演和过程监测,并用于改进气候模式的参数化方案。  相似文献   

The State of Arts: Sources,Microbial Processes and Ecological Effects of Iron in the Marine Environment     

Shibo Feng  Yuelu Jiang  Zhonghua Cai  Yanhua Zeng  Jin Zhou 《地球科学进展》2019,34(5):513-522

Iron is the fourth most abundant element in the earth's crust, and it often appears as a trace element in the ocean. Iron has a variable valence and diverse functions, and is an important force to regulate marine primary productivity and drive the geochemical cycle in the ocean. Previous studies have shown that iron plays an important role in maintaining primary productivity, coupling matter cycles, and regulating the transformation of biogenic factors. In recent years, with the development of microbial ecology, iron research has enter more in-depth levels, including microbial-driven iron oxidation-reduction behavior, metabolic processes, and interactions with other major elements(C/N/P). This paper attempts to review the latest progress of iron, focusing on the published literatures of the past fifteen years. Firstly, we explained the sources and occurrence states of iron in the ocean (such as dissolved, colloidal, granular and organic state); Secondly, we reviewed the types and process mechanisms of microbial-mediated iron redoxbehavior (for example nitrate oxidation, and biological reduction, etc.); Finally, we summarized the coupling relationship between iron and C/N/P cycle. Additionally, the ecological roles of iron in specific ecological event (for instance algal bloom) has also been described. Furthermore, the "chemical-biological-physical" theoretical framework for marine iron research is also discussed. The purpose of this paper is to provide more information for marine microecological research and their effects on iron cycle under changing environment, such as global change.  相似文献   

Biological Processes Responsible for Travertine Deposition: A Review and Future Prospect     

Zhijun Wang  Jianjun Yin  Junbing Pu  Daoxian Yuan 《地球科学进展》2019,34(6):606-617

The investigation of biological processes responsible for travertine deposition allows us to better understand the travertine petrographic and geochemical signatures as proxies of climatic and environmental change. This paper reviewed the organisms associated with travertines, the biotic micro-fabrics formed within travertines, the biological processes associated with travertine precipitation and their controls on travertine geochemical properties. Prospects of the future research on biological processes responsible for travertine precipitation were provided. Bacteria, algae and mosses are the most important organisms that involve in the precipitation of travertines. The growth of these organisms leads to the formation of a range of various porosity, crystal fabrics and lamination within travertines. Three main biological processes responsible for travertine deposition can be classified, including \mathrm{①} a process of aquatic plant growth generating a turbulent condition and consequent CO₂ evasion, \mathrm{②} a metabolic (mainly photosynthetic) process mediating carbonate precipitation and \mathrm{③} a ‘surface-control’ process influencing nucleation and crystal growth. These processes play an important role in the migration and transformation of elements in travertine-depositing system and thus determine the properties of water chemistry and geochemistry of carbonate deposits. Travertine deposits have great potential to be valuable records for the geobiological study. Further investigation is required to simultaneously track biotic and abiotic interactions in modern travertine-depositing environments and quantify the contribution of these two processes and apply the results to accurately interpret travertine records.  相似文献