Interannual variability in water storage over 2003-2008 in the Amazon Basin from GRACE space gravimetry, in situ river level and precipitation data

We investigate the interannual variability over 2003-2008 of different hydrological parameters in the Amazon river basin: (1) vertically-integrated water storage from the GRACE space gravimetry mission, (2) surface water level of the Amazon River and its tributaries from in situ gauge stations, and (3) precipitation. We analyze the spatio-temporal evolution of total water storage from GRACE and in situ river level along the Amazon River and its main tributaries and note significant differences between the various parts of the basin. We also perform an Empirical Orthogonal Decomposition of total water storage, river level and precipitation over the whole basin. We find that the 2003-2008 period, is characterized by two major hydrological events: a temporary drought in late 2005 that affected the western and central parts of the basin and very wet conditions peaking in mid-2006, in the eastern, northern and southern regions of the basin. Derivative of basin-average water storage from GRACE is shown to be highly correlated with the Southern Oscillation Index (a proxy of ENSO — El Niño-Southern Oscillation), confirming that the spatio-temporal change in hydrology of the Amazon basin is at least partly driven by the ENSO phenomenon, as noticed in previous studies.     

Use of GRACE time-variable data and GLDAS-LSM for estimating groundwater storage variability at small basin scales: a case study of the Nzoia River Basin

This study integrates time-variable Gravity Recovery and Climate Experiment (GRACE) gravimetric measurements and Global Land Data Assimilation System (GLDAS) land surface models (LSM) in order to understand the inter-annual variations and groundwater storage changes (GWSC) in the Nzoia River Basin in Kenya, using the water balance equation and parameters. From averaged GRACE and GWSC data, the results showed that over the 10-year period, the basin experienced a groundwater depth gain of 6.38 mm year^?1, which is equivalent to aquifer recharge of 298 million cubic metres (mcm) year^?1. The deseasonalized groundwater variation analysis gave a net gain in groundwater storage of 6.21 mm year^?1 that is equal to a groundwater recharge gain of 290 mcm year^?1. The observed results are comparable to the groundwater safe yield of 330 mcm year^?1 as estimated by the Water Resource Management Authority in Kenya. Through cross-plotting and analysis with averaged satellite altimetry data and in situ measurements from rainfall and streamflow discharge, the total water storage change (TWSC) and GWSC in the basin were consistent and closely correlated in variation trends. The inter-annual standard deviation of groundwater change was determined as ±0.24 mm year^?1, which is equivalent to 85% degree of confidence in the obtained results. The results in this study show that GRACE gravity-variable solutions and GLDAS-LSM provide reliable data sets suitable for the study of small to large basin groundwater storage variations, especially in areas with scarce and sparsely available in situ data.     

Integration of GRACE,ground observation,and land-surface models for groundwater storage variations in South Korea

Terrestrial water storage (TWS) comprises all forms of water stored in the Earth’s surface. The gravity recovery and climate experiment (GRACE) twin satellite provides an efficient method of assessing TWS changes (TWSCs) by measuring variations in the Earth’s gravity. GRACE-derived TWS is equivalent to the sum of all forms of water such as surface water, soil moisture, snow water equivalent, and groundwater. Therefore, groundwater storage and its variations can be estimated when other variables are determined. We used Level-3 data (RL 05) to estimate monthly TWSC in South Korea. Data were obtained from land-surface models (LSMs) of global land data assimilation system (GLDAS), ground observations from water management information system (WAMIS) and rural agricultural water resources information system (RAWRIS). GRACE-derived groundwater storage changes (GWSCs) were ?0.18 ± 6.5 cm month^?1 on average, indicating the decrease of groundwater. We validated the GRACE-derived GWSC by comparing the changes with well-derived GWSC obtained from in situ groundwater observation wells of Korean national groundwater monitoring networks (NGMNs). This satellite-based remote-sensing methodology can provide an efficient tool for the nationwide planning and management of groundwater.     

HydroTrend v.3.0: A climate-driven hydrological transport model that simulates discharge and sediment load leaving a river system

HydroTrend v.3.0 is a climate-driven hydrological water balance and transport model that simulates water discharge and sediment load at a river outlet, by incorporating drainage basin properties (river networks, hypsometry, relief, reservoirs) together with biophysical parameters (temperature, precipitation, evapo-transpiration, and glacier characteristics). HydroTrend generates daily discharge values through: snow accumulation and melt, glacier growth and ablation, surface runoff, and groundwater evaporation, retention and recharge. The long-term sediment load is predicted either by the ART-QRT module based on drainage area, discharge, relief, and temperature, or the BQART module that also incorporates basin-average lithology and anthropogenic influences on soil erosion. Sediment trapping efficiency of reservoirs is based on reservoir location in the river network and its volume that determines the residence time of water within the reservoir. Glacial influence is based on the extent of ice cover, equilibrium altitude, and freezing line mobility. HydroTrend v.3.0 captures the inter- and intra-annual variability of sediment flux by using either high-resolution climate observations or a stochastic climate generator for simulations over longer geological intervals. A distributary channel module simulates the flow conditions and transport capacity across a multiple deltaic channel system. Simulations of the Metauro and the Po rivers, in Italy, are used as case studies to demonstrate the applicability of the new model.     

Optimum groundwater locations in the northern United Arab Emirates

Due to the increase in urban and agricultural activities in arid regions, the exploration of new locations of possible groundwater discharge and accumulation is required to augment the limited water resources. In order to locate such discharge areas, it is necessary first to identify zones of high recharge potentials. In such an arid region, like the northern United Arab Emirates (UAE), one of the ways to predict areas of potential groundwater recharge is by understanding the hydrological response of its drainage basins to rainfall events. Due to the scarcity of basic hydrological data, a hydrological model driven mainly by information on the physiographic characteristics, drainage network properties (generated from DEM), and surface cover distribution (generated from satellite images) was used to comprehend the dynamics of surface runoff through hydrographs, and hence water loss in the study area. Results show that the northern UAE is drained by 48 drainage basins emerging from the Oman Mountains. Two‐thirds of these basins drain easterly toward the Gulf of Oman, and one‐third drain westerly toward the Arabian Gulf. These basins are found to be structurally controlled by three major fault trends, which are the NE trend (Dibba zone), NW trend (Ham Zone), and WNW trend (Hatta zone).

The hydrological response of a basin is correlated with its morphological characteristics. Based on these characteristics, and through the application of a cluster analysis, it was feasible to classify the largest basins in the region into four groundwater potentiality groups in accordance with the magnitude of their peak discharges. From this study, it became evident that the downstream area of the two major basins of Ar‐Rafiah and Limhah, and their vicinities are the most probable sites for groundwater accumulation. The drainage systems of these two basins, especially those controlled by major fault lines, play a vital role in transmitting surface–subsurface rainwater from the Oman Mountains, the recharge zone, into the western desert plain, the discharge zone, where freshwater accumulates underground. The study also revealed that a large volume of groundwater is dissipated into the sea along the eastern coast. A detailed examination of MODIS thermal data supports this by revealing cool surface anomalies issuing from the mountain range toward both the western desert plain and the Gulf of Oman following major rainfall events. Thus, the technique used facilitates the prediction of new locations of optimum groundwater resources in the northern UAE. Such a technique could be adopted, with appropriate modifications, elsewhere in arid regions, where groundwater is restricted and subject to greater complexity.     

Influence of neotectonic activity on groundwater salinity and playa development in the Mendha river catchment,western India

The groundwater salinity of Mendha river, one of the important streams that feed Sambhar playa in Rajasthan in western India, was studied to understand the effect of neotectonic activity on groundwater quality and salinity. We attempted to decouple the tectonic control of salinity and its contribution in the development of playa deposits in Rajasthan. Multiresolution, multidate satellite data products such as IRS‐1C, IRS‐1D LISS‐III, PAN and Landsat MSS were digitally enhanced and analysed to model the morphotectonic evolution and hydrological regime of the region. Electrical conductance data from spatially distributed points in the Mendha river basin were correlated with the aquifer geometry deciphered from borehole lithologs and lineaments and major geomorphic features interpreted from satellite images. The results of the study reveal that the aquifer geometry is controlled by subsurface structures that have been influenced by neotectonic activity in the past 8–9 ka, significantly influencing the hydrological regime and salinity of Sambhar playa.     

Linking groundwater simulation and reservoir system analysis models: The case for California’s Central Valley

Groundwater is an important resource. In many developed basins it meets part or all of the water demands. In addition, the management of groundwater resources directly impacts stream flows through stream-aquifer interactions. Yet many reservoir system analysis models that are used for the management of surface water resources either include a simplified representation of the groundwater flow dynamics or rely on surrogate models (linear response functions, artificial neural networks, etc.) which are trained using more complex groundwater models. These approaches may introduce restrictive, sometimes inaccurate, representation of the groundwater flow dynamics and additional modeling steps. In this study a reservoir system analysis model that utilizes an LP solver is linked directly to a non-linear, three-dimensional, finite element groundwater model. The linked model is a general-purpose model and can be applied to any basin. Some of the features of the linked model are showcased by an application to California's Central Valley.     

Reconciling the global terrestrial water budget using satellite remote sensing

Recent retrievals of multiple satellite products for each component of the terrestrial water cycle provide an opportunity to estimate the water budget globally. In this study, we estimate the water budget from satellite remote sensing over ten global river basins for 2003-2006. We use several satellite and non-satellite precipitation (P) and evapo-transpiration (ET) products in this study. The satellite precipitation products are the GPCP, TRMM, CMORPH and PERSIANN. For ET, we use four products generated from three retrieval models (Penman-Monteith (PM), Priestley-Taylor (PT) and the Surface Energy Balance System (SEBS)) with data inputs from the Earth Observing System (EOS) or the International Satellite Cloud Climatology Project (ISCCP) products. GPCP precipitation and PM (ISCCP) ET have less bias and errors over most of the river basins. To estimate the total water budget from satellite data for each basin, we generate merged products for P and ET by combining the four P and four ET products using weighted values based on their errors with respect to non-satellite merged product. The water storage change component is taken from GRACE satellite data, which are used directly with a single pre-specified error value. In the absence of satellite retrievals of river discharge, we use in-situ gauge measurements. Closure of the water budget over the river basins from the combined satellite and in-situ discharge products is not achievable with errors of the order of 5-25% of mean annual precipitation. A constrained ensemble Kalman filter is used to close the water budget and provide a constrained best-estimate of the water budget. The non-closure error from each water budget component is estimated and it is found that the merged satellite precipitation product carries most of the non-closure error.     

卫星重力监测全球地下水储量变化及其特征

地下水储量是水资源管理和陆地表面过程与水循环研究的一个重要参数。然而,由于传统观测技术成本高和空间分辨率低等局限性，很难建立一个全球连续的综合地下水监测网，因此监测全球高时空分辨率的地下水储量及其变化仍是当前的一个挑战。2002年发射的低低卫—卫跟踪“重力恢复与气候试验”(GRACE)重力卫星为高分辨率地监测全球地下水储量及其变化，提供了一种新的可能手段。利用2002年8月~2011年2月的GRACE观测数据估计近10 a的月间隔全球陆地水总储存量，扣除了GLDAS水文模型（全球陆地数据同化系统）中的地表水、冰雪和生物水，得到全球地下水储量时间序列，并分析其季节性和长期变化及其特征。研究结果表明:GRACE探测到全球地下水储量具有明显的季节性变化，例如在南美洲的亚马逊河流域和亚洲中南部的周年振幅达到50 mm，而在澳大利亚南部和非洲北部的周年振幅只有10 mm左右。另外全球地下水储量具有明显的长期变化，如南美洲亚马逊河流域由于洪水造成地下水储量以6 mm/a的速率增加，拉普拉塔地区由于干旱造成地下水储量以7.5 mm/a的速率减少;中国新疆吐鲁番盆地地区的地下水储量以3.1 mm/a的速率减少,中国华北地区的地下水储量以4.8 mm/a的速率下降。     

基于机理模型的兰江洪水复盘分析

为提高洪水预报水位精度，结合水文和水动力模型，对钱塘江 2022 年“6·21”洪水计算过程进行复盘，分析洪水成因。收集降雨量、水位、流量等水文监测数据及水利工程调度信息，建立兰江流域半分布式水文和分段水动力模型，完成模型率定和验证。基于模型分析洪水成因，分析降雨时空变化、梯级水利枢纽调度、区间水库拦蓄对洪水过程的影响。结果表明：洪水主要由自北向南移动的强降雨形成，在水利枢纽调度影响下，洪水水位过程线由尖瘦型演变为头肩型，其中干流水利枢纽调度影响低水水位上涨和消落，上游水库调蓄可有效削减洪峰并推后峰现时间。通过洪水成因分析，在机理模型中加入水利工程调度影响，计算的洪水水位过程与实际更加吻合。     

Remote sensing and active tectonics of South India

The Indian Peninsula in general and its southern part in particular has been thought to be a stable shield area and hence inert to younger earth movements and seismicities. However, in addition to fast relapsing seismicities, the studies carried out by earlier workers during the past three decades indicate possible pulsatory tectonism, at least since the Jurassics. The present study is a newer attempt to identify, analyse, and spatially amalgamate a large number of anomalies visibly displayed by the tectonic, fluvial, coastal, and hydrological systems in remote sensing and ground based datasets/observations, and to finally paint a fair picture on the active tectonic scenario of South India. The study reveals that the phenomena, viz. extensive soil erosion, reservoir siltation, sediment dump into the ocean, preferential migration of rivers, restricted marine regression, shrinkage of back waters, withdrawal of creeks, fall of groundwater table, etc., indicate two E–W trending ongoing tectonic (Cymatogenic) archings along Mangalore–Chennai in the north and Cochin–Ramanathapuram in the south. Intervening these two arches, a cymatogenic deep along Ponnani–Palghat–Manamelkudi exhibiting phenomena opposite to the above is observed. In addition, the characteristic tectonic, geomorphic, and hydrological anomalies observed in 1B satellite FCC data, as well as in the field, indicate N–S trending extensional, NE–SW sinistral, and NW–SE dextral strike slip faults. These anomalies and the tectonic features deduced thereupon, indicate that the southern part of the Indian Peninsula is tectonically active due to the northerly to north–northeasterly directed compressive force related to post collision tectonics. This active tectonic model visualized for South India gives a further clue that the whole Indian plate is whirling like a worm with alternate E–W arching and deepening, along with block and transform faulting from Cape Comorin in the south to the Himalayas in the north.     

An independent component analysis filtering approach for estimating continental hydrology in the GRACE gravity data

An approach based on Independent Component Analysis (ICA) has been applied on a combination of monthly GRACE satellite solutions computed from official providers (CSR, JPL and GFZ), to separate useful geophysical signals from important striping undulations. We pre-filtered the raw GRACE Level-2 solutions using Gaussian filters of 300, 400, 500-km of radius to verify the non-Gaussianity condition which is necessary to apply the ICA. This linear inverse approach ensures to separate components of the observed gravity field which are statistically independent. The most energetic component found by ICA corresponds mainly to the contribution of continental water mass change. Series of ICA-estimated global maps of continental water storage have been produced over 08/2002-07/2009. Our ICA estimates were compared with the solutions obtained using other post-processing of GRACE Level-2 data, such as destriping and Gaussian filtering, at global and basin scales. Besides, they have been validated with in situ measurements in the Murray-Darling Basin. Our computed ICA grids are consistent with the different approaches. Moreover, the ICA-derived time series of water masses showed less north-south spurious gravity signals and improved filtering of unrealistic hydrological features at the basin-scale compared with solutions obtained using other filtering methods.     

Comparison of 1D models of water flow in unsaturated soils

Understanding the interaction between soil, vegetation and atmosphere processes and groundwater dynamics is of paramount importance in water resources planning and management in many practical applications. Hydrological models of complex water resource systems need to include a number of components and should therefore seek a balance between capturing all relevant processes and maintaining data requirement and computing time at an affordable level. Water transfer through the unsaturated zone is a key hydrological process connecting atmosphere, surface water and groundwater. The paper focuses on the analysis of the modelling approaches that are generally used to describe vertical water transfer through unsaturated soil in hydrological models of water resource systems: a physically based approach, using numerical solutions of Richards' equation, and two conceptual models, based on reservoir cascade schemes, are compared. The analysis focuses on the soil water content in the top soil (first meter) and on the outflow from the profile (i.e. recharge to the aquifer). Results show that the water contents simulated by the mechanistic and conceptual models are in good agreement, unless the capillary fringe reaches the top soil (i.e. groundwater table very close to the soil surface). The ability of conceptual models to capture the daily recharge dynamics is generally rather poor, especially when fine textured soils and thick profiles are considered; a better agreement is found when recharge is accumulated over longer time periods (e.g. months). Improvements can be achieved by allowing the number of reservoirs in cascade to vary with changing profile depth, although scientifically sound rules for fixing the number of reservoirs need to be established.     

Water level fluctuations derived from ENVISAT Radar Altimeter (RA-2) and in-situ measurements in a subtropical waterbody: Lake Izabal (Guatemala)

The use of remote sensing techniques in monitoring inland waters has become a powerful tool, considering the amount of ungauged waterbodies all over the world. The water mass balance is an essential subject to take into account in water management activities. The level changes of a lake surface are an indicator of the water mass balance of a basin since they reflect the water storage variations. Space borne altimeters have been successfully used in the last decade to measure lakes, rivers and wetland stages. This study presents the first analysis of Lake Izabal — the biggest lake of Guatemala (Central America) — water level fluctuations using altimetry data and in-situ measurements. Water level variations were obtained from Envisat Radar Altimeter (RA-2) Geophysical Data Records coupled with in-situ measurements. The analysis period included three complete years (2004 to 2006). The rainfall and temperature records over the catchment were analyzed considering that the amount of water feeding the lake, either by the tributaries and/or the groundwater, is driven by the climatic conditions over the lake's catchment. The results obtained show a good agreement between both, altimeter and in-situ datasets (correlation coefficient: 0.83 and rms error: 0.09 m). Lake Izabal water level fluctuations have a seasonal signal forced by the rainy and dry climate seasons in the region. An abrupt lake level rise was found in July 2006 which is correlated to abnormal precipitations in June. We found a connection between the higher/lower extreme values in the lake level variations with rainfall anomalies produced by regional climate changes forced by El Niño Southern Oscillation and the Tropical North Atlantic anomaly.     

Detection of Rossby waves in multi-parameters in multi-mission satellite observations and HYCOM simulations in the Indian Ocean

Rossby waves are difficult to detect with in situ methods. However, as we show in this paper, they can be clearly identified in multi-parameters in multi-mission satellite observations of sea surface height (SSH), sea surface temperature (SST) and ocean color observations of chlorophyll-a (chl-a), as well as 1/12° global HYbrid Coordinate Ocean Model (HYCOM) simulations of SSH, SST and sea surface salinity (SSS) in the Indian Ocean. While the surface structure of Rossby waves can be elucidated from comparisons of the signal in different sea surface parameters, models are needed to gain direct information about how these waves affect the ocean at depth. The first three baroclinic modes of the Rossby waves are inferred from the Fast Fourier Transform (FFT), and two-dimensional Radon Transform (2D RT). At many latitudes the first and second baroclinic mode Rossby wave phase speeds from satellite observations and model parameters are identified. Wavelet transforms of these multi-parameters from satellite observations and model simulations help to discriminate between the annual and semi-annual signal of these Rossby waves. This comprehensive study reveals that the surface signature of Rossby waves in SSS anomalies is likely to be between 0.05 and 0.3 psu in the South Indian Ocean.     

Ground water potential in a semi-arid region of Andhra Pradesh - a geographical information system approach

Continuous and adequate supplies of potable water from ground reservoirs are important for sustained agriculture, industry and domestic use throughout huge semi-arid regions of India. The present paper describes an approach to investigating groundwater potential over extensive geographical areas and illustrates its potential with reference to watershed planning in the large Varaha River Basin (VRB), Andhra Pradesh, India. The method involves the creation of a systematic database of information from satellite data for reconnaissance survey before going for field exploration. Colour composite images from Landsat Thematic Mapper and Indian Remote Sensing (IRS) satellite were used to interpret various thematic maps of the Varaha river basin. SPOT 1 MLA data of band 3 on a 1:250 000 scale was used for improving the accuracy of interpretation of topographic units due to its higher resolution and stereo coverage. Slope and other coverages were derived from topographic maps. The thematic and topographic information was digitized and ERDAS Imagine GIS software was used to analyse this information. Groundwater potential zones were delineated through subjective weights assigned to interpreted thematic and derived topographic units according to their likely infiltration capacities. Seven categories of groundwater potential ranging from very good to poor were derived automatically. Field measurements were then made within a selection of these categories to check the groundwater potential at selected sites. The validity and effectiveness of using remote sensing and GIS techniques for improving the targeting of field observations for groundwater for a huge river basin is shown by comparing the inferred groundwater potential with the field measurements.     

基于北京一号小卫星的北京及周边五大流域地表水资源监测与分析

地表水作为水资源的重要组成部分,能从特定角度反映水资源状况。研究了基于北京一号小卫星影像的地表水体分类标准、水信息提取方法,并对2007年北京及周边五大流域地表水资源进行了动态监测,同时结合气象水文数据分析其时空分布规律、年内变化特征和变化原因。研究表明:① 利用北京一号小卫星32 m多光谱影像辅以4 m全色影像,基于面向对象分类等方法可以较准确地提取各类地表水信息;② 2007年北京及周边五大流域地表水资源变化特征与该区域2007年平均降水量、降水量的年内变化以及水库调蓄等有关。     

Coupling real-time control and socio-economic issues in participatory river basin planning

In this paper an approach for coupling real-time control and socio-economic issues in participatory river basin planning is presented through a case study. It relies on the use of Bayesian Networks (Bns) to describe in a probabilistic way the behaviour of farmers within an irrigation district in response to some planning actions. Bayesian Networks are coupled with classical stochastic hydrological models in a decision-making framework concerning the real-time control of a water reservoir network. The approach is embedded within the framework of the Participatory and Integrated Planning (PIP) procedure.     

利用多源数据分析呼伦湖地表与地下水的动态变化

湖泊对揭示区域环境演变特征与规律具有重要意义。为研究近30 a呼伦湖地区地表水面积与地下水水储量的变化,利用Google Earth Engine（GEE）云平台处理了1986~2018年间所有Landsat卫星影像。结合卫星测高所获得的水位数据,得到呼伦湖的水体面积长时间变化序列,并将其划分为4个阶段：2000年之前的平稳扩张阶段,2000~2012年的骤减阶段,2013~2015年为迅速回升阶段,2016年之后的稳定阶段。在此基础上,综合利用降水、蒸发以及河流流量等模型数据对其变化原因进行了全面分析,揭示了3个因素在4个阶段所发挥的不同作用。最后,利用水量平衡公式推算出地下水储量变化,分析了（1986~2013年）呼伦湖地下水水储量变化趋势,结果表明该地区地下水水储量持续减少。     

Land surface air temperature mapping using TOVS and AVHRR

Surface air temperature is an important variable in land surface hydrological studies. This paper evaluates the ability of satellites to map air temperature across large land surface areas. Algorithms recently have been developed that derive surface air temperature using observations from the TOVS (TIROS Operational Vertical Sounder) suite of instruments and also from the AVHRR (Advanced Very High Resolution Radiometer), which have flown on the NOAA operational sun synchronous satellites TIROS-N NOAA-14. In this study we evaluate TOVS soundings from NOAA-10 (nominal local time of overpass 7:30 a.m./p.m.) and data from AVHRR aboard NOAA-9 (nominal local time 2:30 a.m./p.m.). Instantaneous estimates from the AVHRR and TOVS were compared with the hourly ground observations collected from 26 meteorological stations in the Red River-Arkansas River basin for a 3-month period from May to July 1987. Detailed comparisons between the satellite and ground estimates of surface air temperatures are reported and the feasibility of estimating the diurnal variation is explored. The comparisons are interpreted in the geographical context, i.e. land cover and topography, and in the seasonal context, i.e. early and midsummer. The results show that the average bias over the 3-month period compared with ground-based observations is approximately 2°C or less for the three times of day with TOVS having lower biases than AVHRR. Knowledge of these error estimates will greatly benefit use of satellite data in hydrological modelling.