CHARACTERISTICS OF SEDIMENT TRANSPORT ALONG A RIVER REACH WITH A RESERVOIR

Based on long-term measurements at three gauging stations, Toudaoguai, Fugu and Hequ, and one meteorological station, this article discusses the features of discharge (Q) and sediment concentration (Cs) of a river reach of the Yellow River with a reservoir located in the Loess Plateau. The impacts of the local sub-watershed between Toudaoguai and Fugu gauging stations on sediment budget to the Yellow River have been analyzed. In addition, the deposition processes in the Tianqiao Reservoir have been investigated. Results show over 80% of the precipitation that falls in the local subwatershed is unable to contribute to the Yellow River runoff process. It is found that the annualmaximum sediment concentration is usually less than 30 kg/m^3 during flood seasons at Toudaoguai Gauging Station, but the sediment concentration varies dramatically at Fugu Gauging Station. About 35% of the sediment eroded in the sub-watersheds between Toudaoguai and Fugu gauging stationswas produced from the Huangfuchuan sub-watershed which has a drainage area accounting only for 10% of the drainage area between Toudaoguai and Fugu gauging stations. The Tianqiao Reservoir generally has deposition during the summer flood season, and scouring during the non-flood season.On average, over 85% of deposited sediment in the reservoir occurs in the 12 km long lower reservoir reach. The volume of annual deposition in the reservoir mainly depends on the volume of water from the local region between Hequ and Fugu gauging stations.     

科尔沁沙丘-草甸过渡带人工杨树林蒸腾耗水特征

采用热扩散茎流计和自动气象站对科尔沁沙丘-草甸过渡带人工杨树林的树干液流和环境因子进行长期连续监测。结果表明：不同天气条件下茎流速率差异明显,晴天各因子昼夜波动特征明显,雨天波动幅度小,阴天介于二者之间;不同天气类型影响茎流速率的主要气象因子不同,晴天茎流速率与净辐射相关性最高（偏相关系数为0.72）,阴天与气温相关性最高（偏相关系数为0.69）;整个生长季典型晴天日平均茎流速率近似服从二次曲线,夏季大于春季和秋季,不同月份茎流速率日内变化差异显著,表现在峰值大小、液流启动时间和峰值出现时间不同;林地供水充足,持续干旱和雨后茎流速率没有显著差异,杨树蒸腾所需水分主要来自地下水,地下水位在09：00-17：00下降明显,且茎流速率越大下降幅度越大;不同胸径杨树茎流速率对各气象因子的时滞时间相同,而不同月份茎流速率对各气象因子的时滞时间不同。     

基于电磁感应技术的塔里木盆地北缘绿洲土壤盐分空间变异特性

土壤盐渍化是影响绿洲农业生产、抑制作物生长的主要生态环境问题。当前,将电磁感应技术与地面实测技术相结合是监测土壤盐渍化分布及其变化的先进方法。本文以新疆渭干河-库车河三角洲绿洲为研究区,以电磁感应仪在水平模式下（EM_H）和垂直模式下（EM_V）所获取的土壤表观电导率数据以及野外实测数据为基础,通过建立EM_V和EM_H与土壤盐分含量及组成元素的多元线性回归模型,采用泛克里格法（Universal Kriging）对研究区两个关键季节（干季、湿季）的土壤盐分含量及组成的空间变异特征进行了分析。结果表明：研究区干季和湿季表层盐渍土含盐量均与EM_V和EM_H具有良好的相关性,以EM_V+EM_H为自变量建立的土壤盐分解译模型的精度较高,且通过0.01水平检验;研究区干、湿两季的表层土壤含盐量数据符合P-P正态分布,空间分布均呈现强相关性;采用能够充分考虑到干旱区表层土壤盐分空间变异的球状套合模型,能够更好地拟合土壤表层含盐量的空间结构;研究采用泛克里格法将解译出的土壤盐分及其主要组成离子（Na⁺、Cl^-）含量进行空间插值分析,其变化趋势与土壤含盐量的变化趋势基本一致,因而采用电磁感应技术可以有效地监测不同季节干旱区绿洲土壤盐分及其组成的空间变化。     

The influence of rainfall on PR radar measurement of ocean surface wind speed and its calibration

Rain can significantly degrade the wind vector retrieval from Precipitation Radar(PR) by three mechanisms, namely, two-way rain attenuation, rain volume-backscattering, and ocean surface roughening from the rain splash effect. Here we first derive the radar equation for PR in rainy conditions. Then we use the rain attenuation model for Ku band, volume backscatter model for spherical raindrops and PR–TMI(TRMM Microwave Imager, TMI) matchup datasets from June to August in 2010 to solve the radar equation, and quantitatively analyze the influence of rainfall on PR radar measurement of ocean surface wind speed. Our results show that the significant effect of rain on radar signal is dominated by two-way rain attenuation and rain splash effect, and the effect of rain volume-backscattering is relatively the weakest, which can even be neglected in rain-weak conditions. Moreover, both the two-way rain attenuation and rain splash effect increase with the increasing of integration rain rate and incident angle. Last, we combine volume-backscattering effect and splash effect into a simple phenomenological model for rain calibration and select three typhoon cases from June to August in 2012 to verify the accuracy of this model. Before calibration, the mean difference and mean square error(MSE) between PR-observed ? 0 and wind-induced ? 0 are about 2.95 dB and 3.10 dB respectively. However, after calibration, the mean difference and MSE are reduced to 0.64 dB and 1.61 dB respectively. The model yields an accurate calibration for PR near-nadir normalized radar cross section(NRCS) in rainy conditions.     

A sensitivity analysis of lake water level response to changes in climate and river regimes

Lake water level regimes are influenced by climate, hydrology and land use. Intensive land use has led to a decline in lake levels in many regions, with direct impacts on lake hydrology, ecology and ecosystem services. This study examined the role of climate and river flow regime in controlling lake regimes using three different lakes with different hydraulic characteristics (volume-inflow ratio, CIR). The regime changes in the lakes were determined for five different river inflows and five different climate patterns (hot-arid, tropical, moderate, cold-arid, cold-wet), giving 75 different combinations of governing factors in lake hydrology. The input data were scaled to unify them for lake comparisons. By considering the historical lake volume fluctuations, the duration (number of months) of lake volume in different ‘wetness’ regimes from ‘dry’ to ‘wet’ was used to develop a new index for lake regime characterisation, ‘Degree of Lake Wetness’ (DLW). DLW is presented as two indices: DLW₁, providing a measure of lake filling percentage based on observed values and lake geometry, and DLW₂, providing an index for lake regimes based on historical fluctuation patterns. These indices were used to classify lake types based on their historical time series for variable climate and river inflow. The lake response time to changes in hydrology or climate was evaluated. Both DLW₁ and DLW₂ were sensitive to climate and hydrological changes. The results showed that lake level in high CIR systems depends on climate, whereas in systems with low CIR it depends more on river regime.     

山西省2007年酸雨特征分析及成因初探

本文利用五台山、大同、太原、长治、侯马5个酸雨观测站2007年1月～12月的酸雨观测资料,进行了分析,结果表明：五台山酸雨出现频率最高（85．96％）,大同酸雨频率最低（36．36％）;侯马站年降水pH值最低（4．09）,酸雨强度最强,大同的年降水pH值最高（5．36）,酸雨程度最弱;各站pH值最低值一般出现在秋、冬和春季,说明与采暖期燃煤有关。山西酸雨的成因主要与工业结构以及气象因素有关。     

云南临沧市3次罕见雨雪天气对比分析

利用MICAPS资料,对临沧市近年出现的3次罕见雨雪天气从环流特征、冷空气特点和物理量场进行分析,得出:3次雨雪天气过程都是在有利的天气形势背景下发生的,冷空气的强弱和水汽来源的不同,以及水汽通量散度、垂直速度和假相当位温分布的差异导致了雨雪过程降水量的不同.     

淮河洪涝年7月上旬环流特征与近10年平均环流特征差异分析

利用NCEP 1998-2007年分析资料,分析了2007年、2005年和2003年3个淮河大洪水年7月上旬逐日各层的位势高度、温度、水汽和风场等资料.分析结果表明:这3个洪水年和近10年平均场的大尺度环流背景、高低空急流、水汽输送特征等存在显著差异.东亚夏季风异常是这3年淮河流域洪涝出现的主要原因.同时,这3年西北太平洋副热带高压均较历史同期偏强,西伸脊点偏西;华北南部到黄淮距平风场上有较常年明显的偏北气流,副热带高压西北侧850hPa低空急流较常年平均偏强6m·s-1以上,南北两支气流交汇区正好位于淮河流域;在200hPa上淮河流域处于异常的高空急流入口南侧或受较常年偏强的反气旋环流控制之下;从整层水汽通量距平分析,南海是这3个淮河洪涝年的主要水汽源地.     

近50年来长江中下游汛期暴雨变化特征

基于1960～2008年逐日降水观测资料,分析了长江中下游汛期暴雨的气候分布特征、年际、年代际变化以及趋势变化特征。结果表明,该区域汛期暴雨分布呈现南部多、向北递减的总格局。最大暴雨量中心位于江西北部,其形成可能与地形因素有关。在年际尺度上,该区域暴雨量、暴雨强度存有准两年及6～8年的周期变化特征;从年代际尺度看,在时间域上,存在12～14年的周期变化。具体地,汛期区域平均暴雨量、频次在1960年代至1980年代是一个相对平稳的时期,1990年代开始则进入一个高值期,21世纪以后又开始回落。相比较而言,暴雨强度的年代际变化不显著。在空间域上,进入21世纪后随着雨带向淮河流域推进,暴雨量、频次、强度在苏北、皖北增强。从趋势分析看来,过去50年汛期暴雨量、频次呈现较大范围的增加趋势。暴雨强度也表现一定程度的增加趋势。     

淮河大水年的地热涡活动特征及预测途径探讨

通过对2003年地温场的演变形势分析,讨论了引发2003年汛期淮河大水的主要原因。指出：冬季淮河流域有地热涡活跃和缅甸北中部或我国西部中段有6．5级以上强震发生是淮河发生大水的两个必要条件。