Prediction of chlorophyll a concentration using HJ-1 satellite imagery for Xiangxi Bay in Three Gorges Reservoir简

Since the impoundment of the Three Gorges Reservoir in 2003, algal blooms have frequently been observed in it. The chlorophyll a concentration is an important parameter for evaluating algal blooms. In this study, the chlorophyll a concentration in Xiangxi Bay, in the Three Gorges Reservoir, was predicted using HJ-1 satellite imagery. Several models were established based on a correlation analysis between in situ measurements of the chlorophyll a concentration and the values obtained from satellite images of the study area from January 2010 to December 2011. Chlorophyll a concentrations in Xiangxi Bay were predicted based on the established models. The results show that the maximum correlation is between the reflectance of the band combination of B4/（B2＋B3） and in situ measurements of chlorophyll a concentration. The root mean square errors of the predicted values using the linear and quadratic models are 18.49 mg/m3 and 18.52 mg/m3, respectively, and the average relative errors are 37.79% and 36.79%, respectively. The results provide a reference for water bloom prediction in typical tributaries of the Three Gorges Reservoir and contribute to large-scale remote sensing monitoring and water quality management.     

Water issues and prospects for hydrological science in China简

<正>As a country with one of the world’s most rapidly developing economies,China is home to wonderful opportunities for its people and the nation as a whole.An essential element for continued economic prosperity is a water supply of guaranteed quality and quantity,providing critical insurance for food safety,health,and political stability.However,China’s economic success has come with serious water resources problems,intensified by human activities and climate change.The nation is now facing extreme levels of water pollution,soil erosion,and sedimentation,along with floods,droughts,and urban storms.Taken together,these impacts have provided a serious headwind to socioeconomic development in China.This article discusses the problems and emerging opportunities for the coming generation of water scientists and engineers.     

Estimation of discharge and its distribution in compound channels简

Results of research into a compound channel having width ratio(?)in excess of 11 are presented in the form of boundary shear distributions across the compound cross section.New relationship is derived between the percentage of shear carried by the flood plains(%)fp S and the percentage of area occupied by the flood plains(%)fp A.The equation so derived is taken as the basis to develop a new methodology to predict the stage discharge relationship specifically for wide compound channels using Darcy’s friction factor(f)for the main channel and flood plain regions.The methodology also is used for compound channels with smaller width ratios by applying the appropriate relation for%fp S derived earlier by different researchers and seems to work well.Next,as a corollary to the methodology,separate formulae are proposed to estimate flow distribution in main channel and flood plain regions.The proposed method and its corollary are tested for their validity against well-published small-scale data series of previous researchers along with some large-scale data series from EPSRC-FCF(A-Series)compound channel experiments and very good agreement is observed between the measured values and predicted values for total flow as well as zonal distribution of flow.The methodology is also applied to some compound river section data published in literature and is found to serve well the purpose of predicting flow in real world application.This new method gives the least RMS value of error for discharge prediction compared with some other well-known methods used for estimating stage-discharge relation in compound channels by considering all data sets.     

Single-phase and two-phase flows through helical rectangular channels in single screw expander prototype简

The CFD simulations are carried out for the flows in a horizontally oriented helical pipe with various inlet sectional liquid holdups and coil pitches （ H ） . The development of the pressure fields for the single phase air flow and the air-water two-phase flow through the helical rectangular channels is studied. The points with a higher pressure often become the position of expansion leakage. The liquid phase distribution at these points can prevent the leakage of air. It is shown that the increase of the inlet sectional liquid holdup may increase the local liquid holdup at the outmost side of the helical channel. Based on the published pressure drop correla-tion, a new modified relation for predicting the pressure drop in the helical rectangle channel is proposed.     

Flood risk control of dams and dykes in middle reach of Huaihe River简

Three stochastic mathematical models for calculation of the reservoir flood regulation process, river course flood release, and flood risk rate under flood control were established based on the theory of stochastic differential equations and features of flood control systems in the middle reach of the Huaihe River from Xixian to the Bengbu floodgate, comprehensively considering uncertain factors of hydrology, hydraulics, and engineering control. They were used to calculate the flood risk rate with flood regulation of five key reservoirs, including the Meishan, Xianghongdian, Nianyushan, Mozitan, and Foziling reservoirs in the middle reach of the Huaihe River under different flood frequencies, the flood risk rate with river course flood release under design and check floods for the trunk of the Huaihe River in conjunction with relevant flood storage areas, and the flood risk rate with operation of the Linhuaigang Project under design and check floods. The calculated results show that （l） the five reservoirs can withstand design floods, but the Xianghongdian and Foziling reservoirs will suffer overtopping accidents under check floods; （2） considering the service of flood storage areas under the design flood conditions of the Huaihe River, the mean flood risk rate with flood regulation of dykes and dams from Xixian to the Bengbu floodgate is about 0.2, and the trunk of the Huaihe River can generally withstand design floods; and （3） under a check flood with the flood return period of 1 000 years, the risk rate of overtopping accidents of the Linhuaigang Project is not larger than 0.15, indicating that it has a high flood regulation capacity. Through regulation and application of the flood control system of the Linhuigang Project, the Huaihe River Basin can withstand large floods, and the safety of the protected area can be ensured.     

Numerical simulation of hull/propeller interaction of submarine in submergence and near surface conditions简

Hull/propeller interaction is of great importance for powering performance prediction. The features of hull/propeller interaction of a submarine model with a high-skew five blade propeller in submergence and near surface conditions are numerically simulated. The effect of propeller rotation is simulated by the sliding mesh technique. Free surface is captured by the volume of fluid （VOF） method. Computed results including resistance, thrust, torque and self-propulsion factor are compared with experimental data. It shows fairly good agreement. The resistance and wave pattern of the model at different depths of submergence are computed. And the thrust, torque and self-propulsion factor of the model in submergence and near surface condition are compared to analyze the effect of free surface on self-propulsion performance. The results indicate that free surface has more influence on resistance than that on self-propulsion factors.     

Equivalent pipe algorithm for metal spiral casing and its application in hydraulic transient computation basedon equiangular spiral model简

For the metal spiral casing of water turbines, a new equivalent pipe algorithm is developed based on the idea of equiangu-lar spiral. Prototype tests and computations are carried out to investigate the hydraulic transient characteristics. The computation re-sults by using the new model are in a good agreement with the prototype test data with respect to the maximum speed of the tur-bine-generator unit, the maximum water hammer pressure in the spiral casing and the maximum vacuum in the draft tube. The propo-sed method is a significant improvement over the conventional algorithm with the accuracy increased and the error reduced by about 3%.     

An ocean circulation model based on Eulerian forward-backward difference scheme and three-dimensional,primitive equations and its application in regional simulations简

A two-time-level, three-dimensional numerical ocean circulation model is established with a two-level, single-step Eulerian time-difference scheme. The mathematical model of the large-scale oceanic motions is based on the terrain-following coo-rdinated, Boussinesq, Reynolds-averaged primitive equations of ocean dynamics. A simple but very practical Eulerian forward-back-ward method is adopted to replace the most preferred leapfrog scheme as the time-difference method for both barotropic and barocli-nic modes. The forward-backward method is of the second order of accuracy, requires only once of the function evaluation per time step, and is free of the computational mode inherent in the three-level schemes. It is superior in many respects to the original leapfrog and Asselin-filtered leapfrog schemes in the practical use. The performance of the newly-built circulation model is tested by simula-ting a barotropic （tides in marginal seas of China） and a baroclinic phenomenon （seasonal evolution of the Yellow Sea Cold Water Mass）, respectively. The three-year time histories of four prognostic variables obtained by the POM model and the two-time-level model are compared in a regional simulation experiment for the northwest Pacific to further show the reliability of the two-level scheme circulation model.     

GRACE 重力卫星探究我国华北地区陆地水储量变化

利用 GRACE( gravity recovery and climate experiment) 卫星 2003- 2013 年资料分析了华北地区陆地水储量变化, 并与同时间段的 CPC( climate prediction center) 、GLDAS( global land data assimilation system) 水文模型进行比较, GRACE 与 CPC 和 GLDAS 的相关系数分别为 0.679、0.817, GRACE 与 GLDAS 相关性更强。得出结论: 2003- 2013 年华北地区陆地水减少, 变化率为- 1. 8 km3 / a, 扣除地表水后, 地下水变化率为- 1. 3 km3 / a。其中, 2003- 2004 年地下水有所增加, 2005- 2013 年下降, 2010 年以后下降趋势变缓。GRACE 反演与水文模型模拟结 果显示, 2006、2009 年的等效水柱高( equivalent water heig ht , EWH) 均明显小于长期平均值, 并且 GRACE 最值对应月份异常, 对比国家统计局数据分析结果, 这两年水资源总量、地表水资源量、地下水资源量处于低谷区, 这与同年发生的自然灾害相对应。     

基于GRACE重力数据反演黄河流域陆地水储量变化

基于GRACE重力卫星数据反演黄河流域2002-2013年陆地水储量变化,并通过GLDAS验证GRACE反演结果。在此基础上采用皮尔逊相关系数法进一步探究陆地水储量与降水、气温、蒸散和植被NDVI的关系。结果表明:基于GRACE数据能够较好地反演陆地水储量; 2002-2013年间黄河流域的水储量以0.56 cm/a的速度减少,且具有明显的季节特征,水储量在1-6月呈亏损状态,7-12月呈盈余状态;对黄河流域水储量变化与降水、气温、蒸散和NDVI进行滞后性分析,表明其与降水、蒸散、NDVI有两个月的滞后效应,与气温为3个月。     

GRACE卫星数据在海河流域地下水年开采量估算中的应用

结合GRACE卫星数据和全球陆面数据同化系统GLDAS数据,反演了2004—2009年连续72个月的海河流域地下水储量变化。在此基础上,结合2004—2009年海河流域水资源公报的降水量、地下水开采量数据,建立了地下水年开采量与GRACE地下水储量年变化、年降水量的二元回归模型。利用GRACE卫星数据和GLDAS数据反演的地下水储量年变化与由地下水位观测数据计算出的地下水储量年变化相关性较强,其R2为0.804;基于GRACE地下水储量年变化数据与年降水量数据,对地下水年开采量的估算结果良好,建立的回归模型的R2为0.787,表明利用GRACE卫星数据对地下水年开采量进行估算是可行的,是传统地面调查的良好补充。     

2015年黄河流域陆地水储量变化

为研究2005—2015年黄河流域陆地水储量变化,基于GRACE RL05重力数据及全球陆面同化系统模型GLDAS进行陆地水储量反演,通过排除煤炭开采引起的区域质量变化提高反演精度,并分析降水、地下水变化对陆地水储量变化的影响。初步结果表明：在时间上,由GRACE卫星数据反演的黄河流域在2005—2015年陆地水储量变化趋势为-5.20 mm/a,2005—2006年的变化趋势达到-0.91 mm/月,各年内仅7—9月份呈现盈余状态;在[JP2]空间上,流域西部呈现为盈余状态,流域东部呈现为亏损状态;煤炭开采量转换的等效水高变化趋势为-1.95 mm/a,[JP]扣除该水高趋势得到更精确的陆地水储量变化趋势为-3.25 mm/a,其对传统陆地水储量反演结果精度的影响不可忽略;此外,降水与地下水变化分别是导致上、下游区域陆地水储量变化的重要因素。本研究综合考虑煤炭开采量影响,有助于提高传统陆地水储量反演方法精度。     

2002—2021年中国陆地水储量及其组分变化分析

为深入探讨中国2002年4月至2021年3月陆地水储量(TWS)及其组分的变化情况,采用基于分解-集成思想的VMD-LSTM组合预测模型插补GRACE重力卫星和其后续卫星GRACE-FO间断期的数据,利用Theil-Sen斜率分析法和Mann-Kendall趋势检验法研究中国九大流域TWS及其组分的时空演变规律,并基于随机森林法初步分析TWS各组分对TWS的相对贡献率。结果表明:VMD-LSTM模型能够有效插补中国GRACE序列间断期数据,绝大多数区域的纳什效率系数大于 0.6、相关系数大于0.9、均方根误差小于2cm,插补精度显著提高;TWS变化和地下水储量变化趋势具有较好的空间一致性,除东南诸河片、珠江流域片和长江流域片外,其他流域TWS均呈下降趋势,这主要由地下水亏损导致;西部干旱半干旱地区和华北地区TWS主要受地下水储量的影响,相较于干旱半干旱地区,湿润半湿润地区的TWS受冠层水储量和土壤水储量的影响较大。     

海河平原地下水储量变化的重力卫星反演和流域水量平衡

南水北调工程向华北输水与地下水压采的实施,一定程度改变了海河平原供用水格局,影响了海河平原的地下水储量。准确监测地下水储量变化是水安全保障和地下水战略储备的基础。本研究以水资源公报数据为基准,比较了重力卫星(GRACE)不同的信号处理方法和相关产品,反演了2003—2020年海河流域总水储量及其平原区地下水储量变化,分析了海河流域2000—2019年供用水结构变化和水量平衡关系,量化了总水储量变化对流域蒸散发估算的影响。结果表明：GRACE JPL Mascons数据反演的海河平原地下水储量变化与水资源公报数据的决定系数最高;2003—2020年海河平原地下水储量总体分3阶段呈下降趋势,2003—2011年、2012—2015年和2016—2020年的下降速率分别约为-23.9±1.3亿m³/a、-75.5±5.3亿m³/a、-37.3±2.6亿m³/a;在不考虑海河流域年总水储量变化条件下估算的2003—2019年多年平均蒸散量(521 mm/a),与考虑年总水储量变化的多年平均蒸散量(530 mm/a)相差约10 m...     

基于GRACE和GRACE-FO的黄河流域陆地水储量及影响因素分析EI北大核心CSCD

基于GRACE和GRACE-FO卫星陆地水储量遥感数据,采用长短期记忆(LSTM)神经网络模型,结合水量平衡方程和全球陆地数据同化系统(GLDAS)重建GRACE与GRACE-FO间的陆地水储量变化量,分析黄河流域2002年4月至2020年3月陆地水储量变化特征,探究影响陆地水储量变化的环境因子。结果表明:LSTM模型可以有效填补GRACE与GRACE-FO间的陆地水储量变化量;黄河流域陆地水储量呈明显下降趋势,上、中、下游下降趋势依次增大,陆地水储量与地下水储量的变化特征高度相关;黄河流域上、中、下游年陆地水储量变化量与年降水量和年干燥度指数呈极显著相关关系,表明黄河流域陆地水储量变化受到降水和蒸散发的影响。     

黄淮海地区 2003- 2014 年 GRACE 水储量时空变化

利用2003-2014年GRACE时变重力场数据反演黄淮海地区水储量变化,并与同期降水数据比较,分析其年际与年内变化特征,结果表明:时间上,2003-2014年黄淮海地区水储量呈现下降趋势,下降速率约0.42mm/月,其子流域海河和淮河流域下降速率分别为0.52mm/月和0.28mm/月;年内仅2月、9月和12月水储量盈余,9月水储量最大,为9.86mm,6月水储量达到最大盈亏量,约56.65mm;空间上,水储量变化整体上由南往北递减,海河流域水储量较淮河流域亏损严重,但随季节变化水储量亏损状态由南向北得到缓解,到冬季水储量呈现盈余;水储量空间变化主要受降雨影响,同时还受区域农业布局和作物灌溉影响。GRACE数据可为黄淮海地区水储量变化研究带来便利,为区域水资源的科学管理和规划提供依据。     

基于 GRACE 的柴达木盆地水储量变化

水储量是反映区域水资源变化和水量平衡的重要指标,重力反演与气候实验(GRACE)卫星数据为大尺度的水储量变化评估提供了数据支撑。应用2003-2015年的GRACE RL05时变重力场数据并结合地面实测资料,研究柴达木盆地的水储量时空变化特征及其归因。结果表明:13年间柴达木盆地水储量变化呈上升趋势,月平均上升速度约0.26mm;多年平均水储量变化幅度由南向北增量递减,变化幅度8.29~69.38mm;研究区水储量增加与降水量增多的趋势一致。基于GRACE时变重力场反演水储量的方法,为西北资料稀缺地区的水储量变化评估提供了重要支撑。     

利用GRACE时变重力场探测长江流域水储量变化

由于水储量分布不均以及拟合条件不完善,传统水储量探测方法存在局限性,而GRACE(Gravity Recovery and Climate Experiment)重力卫星克服了这些局限,为探测陆地水储量变化提供了新思路。利用CSR(Center for Space Research)提供的GRACE时变重力场模型,辅以P4M6去相关滤波以及高斯平滑滤波等,反演了长江流域2003~2013年陆地水储量变化,采用GLDAS（global land data assimilation system）和WGHM（WaterGAP Global Hydrology Model）水文模型进行对比验证,并对计算得到的水储量时变序列进行趋势项分析。结果表明,GRACE时变重力场能较精确地反演长江流域水储量变化;长江流域水储量呈缓慢增长趋势,增长速度约为0.6 cm/a,长江流域中下游区域水储量增长速度明显大于长江上游区域。