Long-term Streamflow Forecasting Based on Ensemble Streamflow Prediction Technique: A Case Study in New Zealand

Streamflow forecasts are essential for optimal management of water resources for various demands, including irrigation, fisheries management, hydropower production and flood warning. Despite operational application of Ensemble Streamflow Prediction (ESP) for long-range streamflow forecasts in United States of America by the National Weather Service River Forecast System, no such approach has been explored in New Zealand. The objective of the present paper is to explore ESP-based forecasts in New Zealand catchments, highlighting its capability for seasonal flow forecasting. In this paper, a probabilistic forecast framework based on ESP technique is presented, with the basic assumption that future weather patterns will reflect those experienced historically. Hence, past forcing data (input to hydrological model) can be used with the current initial condition of a catchment to generate an ensemble of flow predictions. In the present study employs the ESP-based approach using the TopNet hydrological model with a range of past forcing data and current initial conditions. An ensemble stream flow predictions which provide probabilistic hydrological forecasts, reflecting the intrinsic uncertainty in climate, with lead time up to three months is presented for the Rangitata, Ahuriri, and Hooker and Jollie catchments in South Island, New Zealand. Verification of the forecast over the period 2000-2010 indicates a Ranked Probability Skill Score of 23 to 69 % (over climatology) across the four catchments. In general, improvement in ESP forecasting skill over climatology is greatest in summer for all catchments studied. The ESP based forecast exhibited higher skill for a greater percentage of the forecasting period than climatology. As a result, the ESP forecast can provide better over all information for integrated water resources management purpose. ESP-based forecasts using the TopNet hydrological model have potential as tools for water resource management in New Zealand catchments.     

Hydrologic Modelling Calibration for Operational Flood Forecasting

Runoff prediction in flood forecasting depends on the use of hydrological simulation models and on the input of accurate precipitation forecasts. Reliability of predictions thus obtained hinges on proper calibration of the model. Moreover, when the model is intended to be used systematically in operational forecasting of streamflows, the calibration process must take into account the variation of the model parameters over time, namely in response to changing weather and hydrological conditions in the basin. The goal of the study was to build a process to adjust, on a daily basis, the simulation model parameters to the current hydrological conditions of the river basin, in order for the model to be run operationally for prediction of the streamflow for the next 10-days period, and, thereby, to forecast the occurrence of flood events. Towards this end, hydrological simulations using the HEC-HMS model were performed, using a 3 h period time step. The present communication focuses on the hydrological model calibration and verification processes and on the evaluation of forecasts’ accuracy. The procedure was applied to a part of the largest (full) Portuguese river basin, the Mondego river basin, corresponding to the Aguieira dam section watershed, which comprises an area of 3070 km². Four wet periods, associated with the occurrence of flooding, were selected for the calibration and verification of the model, by adjustment of the model parameters. The results of the study aim to define the optimal calibration parameters values to model the observed streamflow for various hydro-meteorological states, thus enabling adequate prediction of flow in flooding situations and proper application of the model in operational flood forecasting.     

El Niño–Southern Oscillation Link to South Florida Hydrology and Water Management Applications

This study evaluates the relationships between El Niño–Southern Oscillation (ENSO) indices and South Florida hydrology and proposes applications to water management decision making. ENSO relations to the Upper Kissimmee Basin rainfall, watershed for Lake Okeechobee, and cumulative sea surface temperature (SST) anomalies at Niño 3.4 were evaluated. Additionally, relationship between ENSO and Lake Okeechobee inflows, Arbuckle Creek and Josephine Creek flows were analyzed. Hydrology of the northern watersheds of the South Florida water management system is linked to ENSO events. Dry season (November–May) rainfall and flows are higher than average during El Niño years and lower during La Niña years, at the 90% confidence level or higher. The relationship is strongest when the ENSO event is strong as shown with analysis of correlation. ENSO prediction has more certainty than hydrologic prediction for a region. Identifying ENSO and hydrologic relationships can aid water management decision making by providing a lead-time of months to mitigate drought or flood impacts. The ENSO tracking method, which was published in a previous study, is presented to track ENSO strength and event type to provide supplemental outlook on dry season rainfall for Lake Okeechobee operations. Lake Okeechobee, which is the main storage in the South Florida water management system, is regulated by a schedule with a limited band of stage fluctuation because of susceptibility of the Herbert Hoover Dike to wave erosion and seepage at high stages. An early decision making approach to storage management with respect to ENSO related hydrology, is presented based on tracking the strength of ENSO events.     

Flood Vulnerability to Climate Change through Hydrological Modeling

Abstract

Determination of flood vulnerability to climate change is one of the most critical issues for regional water management. Most of the previous studies related to system vulnerabilities to climate change were either a qualitative assessment without the support of hydrological modeling or too complex to apply them to real-world systems. In this study, a modeling and assessment system is proposed to tackle flood vulnerability to the climate change through the incorporation of future climate change scenarios, rainfall-runoff simulation, and vulnerability estimation within an integrated frame. The developed approach is applied to provide decision support for flood management of the Swift Current Creek watershed in Western Canada. The approach not only is useful to determine relative flood vulnerabilities to climate change for supporting flood control planning in the watershed, but also can be extended to estimate vulnerabilities of water quality and water supply to climate change.     

数值天气预报的成功经验对洪水预报的启示

鉴于近30年来数值天气预报有了长足的进步,而在洪水预报中试图推行流域水文模型却进展缓慢这一现状,试图寻找洪水预报精度与数值天气预报精度的差距原因。通过对大气模式(型)和流域水文模型的比较,围绕预报方法及预见期、初始场和边值场、数据同化和融合等问题,论述了数值天气预报的成功经验和流域水文模型在洪水预报应用中存在的问题,期望洪水预报能从中得到启示,在不远的将来实现流域水文模型与数值天气预报的无缝衔接,以进一步提高洪水预报精度,增长洪水预报预见期。     

Fractal characteristics of the middle reach of the Paraná River floodplain during extreme hydrological events

The hydrological events that occur on floodplains are largely defined by precipitation and runoff inputs interacting with their geomorphological characteristics. In the middle Paraná River (MPR), hydrological events have traditionally been studied using water level time series and topographic charts or satellite images of certain floodplain sectors, using the same scale throughout the study area. Different zones of the floodplain were integrated using fractal dimension (FD) to better understand hydrological processes. FD is a useful tool used to characterize the geomorphological complexity of river networks in watersheds. The box-counting method was applied in the MPR floodplain. The result showed that as water levels increase, FD decreases, thereby indicating the direct relation with the hydrological attributes of the floodplain (e.g., duration, magnitude, recurrence of the flood event, and connectivity). This relation constitutes the basis of a new approach of the analysis of hydrological events and their effect on the MPR floodplain. This research provides fundamental information obtained from two hydrological stages and different spatial scales which may complement the method designed to accurately understand the hydrogeomorphological processes that operate on the Paraná River floodplain. It provides a simple parameter that can be used to evaluate the role that each floodplain section plays in attenuating the hydrograph recorded at each gauge analyzed along the river. This information will be useful in the implementation of management policies directed to the mitigation of future hydrological threats generated by alterations in the hydrological regime due to hydroclimatic variations or watershed alterations. The results further strengthen the basis for integrated sustainable planning of the main channel of the Paraná River, its floodplain, and the resources provided by this ecosystem.     

基于集合预报的淮河流域洪水预报研究

建立基于集合预报的淮河具有行蓄洪区流域洪水预报及早期预警模型。在洪水预报中引入数值天气预报以延长洪水预报的预见期。集合预报采用多模式和多分析集合预报技术,考虑初始场的不确定性和模式的不确定性,避免“单一”确定性数值天气预报结果易存在的预报误区。THORPEX 项目支撑的THORPEXInteractiveGrand GlobalEnsemble（TIGGE ）集合预报目的是建立全球交互式预报系统。本文以淮河流域为试验流域,以TIGGE 集合预报（加拿大气象中心（简称CMC,集合成员数为15个）、 欧洲中期天气预报中心（简称ECMWF,集合成员数为51个）、 英国气象局（简称UKMO ,集合成员数为24个）、 美国国家环境预测中心（简称NCEP,集合成员数为15个））驱动构建的水文与水力学相结合的具有行蓄洪区流域洪水预报模型以达延长洪水预报的预见期,新安江模型用于降雨径流计算、一维水动力学模型用于河道洪水演算,实现洪水预报及早期预警。为了进行比较,同时采用地面雨量计观测降水驱动构建的洪水预报模型,对2007和2008年淮河汛期洪水进行检验。结果表明,基于TIGGE 集合预报驱动的洪水预报预见期延长了72~120h ,证明了TIGGE 集合预报可以应用于洪水预报及早期预警。     

山区流域洪涝预报水文与水动力耦合模型研究进展

受人类活动及气候变化的影响,我国山区流域洪涝灾害频发,研制洪涝模拟及预报模型对于流域洪涝灾害防治及水环境综合整治具有重要的理论意义和应用价值。论文评述了洪涝模拟与预报使用的水文及水动力模型的优缺点,指出单一的水文或水动力模型的局限性。基于此,分析并比较了国内外已有的水文模型与水动力模型的不同耦合方式,包括水文模型与水动力模型的串联耦合、水文模型与一维水动力模型的动态单向耦合、水文模型与二维水动力模型的动态单向耦合。总结了各类耦合模型的优势和适用性,评价了已有耦合模型在计算精度、数值格式稳定性和计算效率等方面所取得的创新。论文探讨了流域洪涝发生和发展的水文过程与水动力过程的互馈机制,分析了水文模型与水动力模型新的耦合方法及可行性,介绍了水文与二维及一维水动力的动态双向耦合模型。动态双向耦合模型预期能更加真实地反映流域洪涝发生及发展物理机制,具有提高洪涝模拟预报精度和计算效率的潜力。各类耦合模型各有其自身优势,可以根据流域及城市防洪实际,选取合适的水文与水动力耦合模型,为山区流域洪涝模拟和预报提供技术支持。     

Hydrological simulation approaches for BMPs and LID practices in highly urbanized area and development of hydrological performance indicator system

Urbanization causes hydrological change and increases stormwater runoff volumes, leading to flooding, erosion, and the degradation of instream ecosystem health. Best management practices （BMPs）, like detention ponds and infiltration trenches, have been widely used to control flood runoff events for the past decade. However, low impact development （LID） options have been proposed as an alternative approach to better mimic the natural flow regime by using decentralized designs to control stormwater runoff at the source, rather than at a centralized location in the watershed. For highly urbanized areas, LID stormwater management practices such as bioretention cells and porous pavements can be used to retrofit existing infrastructure and reduce runoff volumes and peak flows. This paper describes a modeling approach to incorporate these LID practices and the two BMPs of detention ponds and infiltration trenches in an existing hydrological model to estimate the impacts of BMPs and LID practices on the surface runoff. The modeling approach has been used in a parking lot located in Lenexa, Kansas, USA, to predict hydrological performance of BMPs and LID practices. A performance indicator system including the flow duration curve, peak flow frequency exceedance curve, and runoff coefficient have been developed in an attempt to represent impacts of BMPs and LID practices on the entire spectrum of the runoff regime. Results demonstrate that use of these BMPs and LID practices leads to significant stormwater control for small rainfall events and less control for flood events.     

Assessing Downstream Impacts of Detention Basins in Urbanized River Basins Using a Distributed Hydrological Model

It is widely recognized that urban development alters infiltration capacity and enhances its spatial variability, but also constrains watercourses into narrow channels making them unable to contain the runoff that is generated by relatively small, but intense, rainfall events. Network of detention basins are designed to reduce the flood peak by temporarily storing the excess storm water and then releasing the water volume at allowable rates over an extended period. This paper shows the use of a distributed hydrological model for the assessment of effectiveness of a network of detention facilities in a heavily urbanized river basin. The distributed hydrological model FEST was used to assess design hydrograph and, in parallel to design the seven detention basins optimized for the specific purpose of maintaining the flow rate within the range of the maximum allowable discharge. This permitted to estimate the design hydrograph considering both the spatial variability of soil infiltration capacity and routing characteristics induced by each detention basins along the main river. Results indicate that on-stream detention ponds can increase duration of the critical event and runoff volume of design flood with possible negative implications on downstream facilities.     

大流域洪水预报与洪水调度管理方法研究

采用水文学与水力学、确定与随机相结合的方法，研究大流域洪水预报与洪水调度管理。确定性模型采用降雨～径流模型的新安江模型和经验预报方案进行流域流量过程预报，一维非恒定流水力学方法进行河道流量与水位以及蓄滞洪预报。随机模型采用线性动态模型进行下断面水位实时预报，最小二乘递推模型进行误差实时校正。以长江支流修水流域为例，采用新安江模型、经验方案进行万家埠与柘林水库入库洪水预报作为水力学计算的上边界条件，采用一维非恒定流水力学方法进行河道洪水流量、水位计算以及分洪计算。该方法为流域的防洪减灾提供了科学的途径。     

基于水文要素的闹德海水库入库沙量预测模型

针对水库调度需要,以闹德海水库为背景开展入库沙量预报研究。首先分析水库的入库水沙特性,以确定入库沙量的主要影响因素;进而研究建立基于水文要素的BP神经网络入库沙量预测模型,并利用历史场次洪水资料进行训练学习。结果表明所选择的产沙因子基本能够反映流域降雨-产沙-输沙过程的传递关系,模型可用于入库沙量预报,指导水库实时水沙调度决策。     

太湖流域大尺度洪涝淹没仿真模型的建立及应用

利用DEM数据及GIS空间分析技术构建洪涝淹没分析模块,将圩区概化为"零维调蓄单元",实现圩区的精细化模拟,与细化后的太湖流域水文水动力学模型耦合,建立能够可靠模拟太湖流域洪涝淹没状态的数学模型.选择2016年流域性暴雨洪涝资料进行模拟验证,与代表站实测水位及实际洪涝灾情分布对比表明,构建的洪涝淹没仿真模型可靠有效.针...     

基于数值天气预报模式的流域中期径流预报

研究耦合天气预报模式的径流预报对提高预报预见期及流域防洪减灾具有重要意义。以金溪池潭水库流域为例,通过尺度转换和气象要素联结实现GEM和GFS两种数值天气模式与新安江模型的单向耦合,进行流域水文模拟以及中期径流预报。日径流过程和次洪过程模拟结果发现耦合数值天气预报模式的流域中期径流预报能够较好地预估一段时间内的径流总量,而对洪峰以及洪水过程预报能力稍有不足。预报误差来源有水文模型误差和降水预报误差两种,且降水预报的误差在水文模型中会有放大的效应,这增加了中期径流预报的不确定性。     

气象集合预报在水文领域中的应用研究进展

集合预报是针对数值预报的不确定性而发展起来的概率预报技术,在水库控制中应用集合预报信息可以延长水文预报有效预见期并且提高预报精度。目前,集合预报已在发达国家中得到广泛的应用。现概括了集合预报的发展过程,并从洪水预警、径流预报、水库调度决策3个方面分析了集合预报在水文领域中的研究进展,探讨了集合预报的检验和集合预报应用中存在的关键问题。     

暴雨洪水相似性判别及外推预估方法

超前洪水预估精度不高一直困扰防洪决策，为解决这一技术难题，提出一种基于暴雨洪水知识的相似性分 析方法，进行洪水预报预测。该方法从历史典型暴雨洪水知识中提取多要素特征指标，基于欧氏距离进行当前与 历史暴雨洪水的特征指标相似性判别，根据判别出的最相似洪水，经“峰-量”联合修正消除非一致性后，实时外推 预估未来洪水过程，构成一套完整的“多要素特征指标提取-历史暴雨洪水相似性判别-实时洪水修正外推预估” 技术。在沂河蒙阴站的应用结果表明，基于“降雨-径流”关系，对判别出的最相似洪水进行修正，显著提高了外推 预估洪水精度，洪峰流量相对误差δQm 的范围降至 10?% 附近，峰现时间绝对误差 ΔT的范围降至±2?h 以内，径流深 相对误差 δR的范围降至±20?% 以内，且随着时间推移，精度水平不断提高。该套技术方法能够挖掘隐含在历史暴 雨洪水数据中的相似性，超前预估当前洪水变化过程，为洪水预报提供一种新的技术参考。     

Basin/Reservoir System Integration for Real Time Reservoir Operation

This paper demonstrates the basin/reservoir system integration as a decision support system for short term operation policy of a multipurpose dam. It is desired to re-evaluate and improve the current operational regulation of the reservoir with respect to water supply and flood control especially for real time operation. The most innovative part of this paper is the development of a decision support system (DSS) by the integration of a hydrological (HEC-HMS) and reservoir simulation model (HEC-ResSim) to guide the professional practitioners during the real time operation of a reservoir to meet water elevation and flood protection objectives. In this context, a hybrid operating strategy to retain maximum water elevation is built by shifting between daily and hourly decisions depending on real time runoff forecasts. First, a daily hydro-meteorological rule based reservoir simulation model (HRM) is developed for both water supply and flood control risk. Then, for the possibility of a flood occurrence, hourly flood control rule based reservoir simulation model (FRM) is used. The DSS is applied on Yuvac?k Dam Basin which has a flood potential due to its steep topography, snow potential, mild and rainy climate in Turkey. Numerical weather prediction based runoff forecasts computed by a hydrological model together with developed reservoir operation policy are put into actual practice for real time operation of the reservoir for March – June, 2012. According to the evaluations, proposed DSS is found to be practical and valuable to overcome subjective decisions about reservoir storage.     

空间均化水文模型及其验证

本文基于空间均化方法构建了空间均化水文模型SAHM.该模型采用基于空间均化方法建立的宏观尺度水文控制方程描述了计算单元内入渗、壤中流和坡面汇流等基本水文过程,在方程中直接包含了土壤饱和导水率和微地形的空间非均匀性,使SAHM在保持传统"点"尺度方程机理性的同时从理论上避免了方程适用尺度和模型应用尺度的不匹配问题.模型在半干旱半湿润的沁河流域上游进行了验证,并对模型参数敏感性进行了分析,结果 表明,模型具有较高的计算精度和计算效率,可用于大中尺度流域水文模拟、水资源评价和洪水预报.     

Variable Streamflow Contributions in Nested Subwatersheds of a US Midwestern Urban Watershed

Quantification of runoff is critical to estimate and control water pollution in urban regions, but variation in impervious area and land-use type can complicate the quantification of runoff. We quantified the streamflow contributions of subwatersheds and the historical changes in streamflow in a flood prone urbanizing watershed in US Midwest to guide the establishment of a future pollution-control plan. Streamflow data from five nested hydrological stations enabled accurate estimations of streamflow contribution from five subwatersheds with variable impervious areas (from 0.5% to 26.6%). We corrected the impact of Missouri river backwatering at the most downstream station by comparing its streamflow with an upstream station using double-mass analysis combined with Bernaola-Galvan Heuristic Segmentation approach. We also compared the streamflow of the urbanizing watershed with seven surrounding rural watersheds to estimate the cumulative impact of urbanization on the streamflow regime. The two most urbanized subwatersheds contributed >365 mm streamflow in 2012 with 657 mm precipitation, which was more than fourfold greater than the two least urbanized subwatersheds. Runoff occurred almost exclusively over the most urbanized subwatersheds during the dry period. The frequent floods occurred and the same amount of precipitation produced ~100 mm more streamflow in 2008–2014 than 1967–1980 in the urbanizing watershed; such phenomena did not occur in surrounding rural watersheds. Our approaches provide comprehensive information for planning on runoff control and pollutant reduction in urban watersheds.     

基于水文模型与遥感信息的植被变化水文响应分析

针对地表覆被改变带来的流域水文响应存在不确定性这一问题,为了探索我国南方山区植被变化下的水文过程时空演变规律,依据东江流域的土地覆被类型,结合野外调查试验与遥感数据提取典型植被特征信息,利用考虑水文、地形、土壤、植被等多要素综合的分布式水文模型DHSVM,对流域内各种典型覆被情景下的水文过程进行模拟,进而分析植被变化引起的径流、蒸发、土壤水变化的响应关系。结果表明:大面积人工种植桉树林,将会对流域水文过程产生较大影响,地表径流深比现状针叶林增大17.5%,蒸散发量减小18.1%,洪峰流量也有所增加,流域洪水灾害发生概率加大;当流域现有针叶林生态系统退化为草地时,多年平均径流量增加24.4%,蒸散量减少25.3%,不利于自然流域的水源含蓄;针叶林、阔叶林和混交林三类森林植被更替对流域的水文过程影响相比其他植被类型要小。研究成果为分析流域变化环境下的水文过程时空演变规律及其生态环境效应提供参考,对我国南方山区水资源管理规划和生态环境保护具有实际意义。