A revised range of variability approach considering the periodicity of hydrological indicators

Comprehensively assessing the hydrological alteration of river flows is a prerequisite for the scientific management, protection, and restoration of rivers. The range of variability approach (RVA), which is based on indicators of hydrological alteration (IHAs), is a widely used method to evaluate hydrological alteration. However, the RVA only considers the frequency of each IHA, neglecting the equally important temporal order of these IHAs. The order of IHA event can be reflected by its periodicity. On the basis of the RVA, in this study, we propose a revised RVA that considers both the frequency and periodicity of IHAs. In the revised RVA, first, the periodic time of each IHA is identified; next, the periodicity alteration (P) of river flow is calculated by comparing the periodic times of the pre‐impact‐period and post‐impact‐period IHAs; finally, P and the frequency alteration(D) in traditional RVA are incorporated into a single index (H) to reflect the overall hydrological alteration. A case study of the Xi Dayang (XDY) Reservoir and rearranged flow suggests that the traditional RVA underestimates hydrological alterations because it neglects the alteration of periodicity. Compared with the traditional RVA and its alternatives, the revised RVA could give a more comprehensive representation of hydrological alteration caused by human and nature impacts. Thus, better protection of an ecosystem could be obtained by applying this method in the evaluation and management of water resources. Copyright © 2013 John Wiley & Sons, Ltd.     

西洞庭湖沉水植物分布格局对环境因子及水文情势差异的响应

沉水植物是湖泊生态系统的重要组成部分,其生产力和分布格局受环境因子特别是水文情势决定.洞庭湖是长江流域重要的大型通江湖泊,近年来受人为干扰和气候变化影响,水文节律与水质等环境因子发生改变,导致沉水植物出现衰退现象,急需开展科学恢复,因此有必要对洞庭湖沉水植物深入研究.本研究选取西洞庭湖为研究区域,于2018年和2019年夏季调查了12处典型生境、98个样点的沉水植物与水深、透明度等11个环境因子,采用独立样本T检验和冗余分析方法对沉水植物与环境因子的关系进行分析,对比年际水文情势变化的影响.结果表明：1）西洞庭湖沉水植物主要在水深较浅、水质更优、水体更为稳定的半阻隔子湖和自由连通的湖湾区分布,在河道及水位波动较大的区域分布较少,有、无沉水植物分布样点间存在显著差异的环境因子为水深、透明度、底泥总磷和pH;2）在有沉水植物分布的样点,沉水植物生物量与pH、水深和水体总磷呈显著相关关系;3）自然连通的季节性淹没湖泊沉水植物生物量在2018年高于2019年,可能与2019年5—8月沉水植物关键生长期出现的涨水过程有关,持续的高水位对沉水植物的生长产生了不利影响.维持自然水文节律、湖泊生境异质性与自由连通性、健康的水质等是恢复西洞庭沉水植物的关键,建议在水深低于3 m、营养盐浓度适中、流速及风浪较小的湖湾区或半阻隔湖泊开展沉水植物恢复.     

Changes in stream flow regime in headwater catchments of the Yellow River basin since the 1950s

The headwater catchments of the Yellow River basin generate over 35% of the basin's total stream flow and play a vital role in meeting downstream water resources requirements. In recent years the Yellow River has experienced significant changes in its hydrological regime, including an increased number of zero‐flow days. These changes have serious implications for water security and basin management. We investigated changes in stream flow regime of four headwater catchments since the 1950s. The rank‐based non‐parametric Mann–Kendall test was used to detect trends in annual stream flow. The results showed no significant trend for the period 1956 to 2000. However, change‐point analysis showed that a significant change in annual stream flow occurred around 1990, and hence the stream‐flow data can be divided into two periods: 1956–1990 and 1991–2000. There was a considerable difference in average annual stream flow between the two periods, with a maximum reduction of 51%. Wet‐season rainfall appears to be the main factor responsible for the decreasing trend in annual stream flow. Reductions in annual stream flow were associated with decreased interannual variability in stream flow. Seasonal stream flow distribution changed from bimodal to unimodal between the two periods, with winter stream flow showing a greater reduction than other seasons. Daily stream flow regime represented by flow duration curves showed that all percentile flows were decreased in the second period. The high flow index (Q₅/Q₅₀) reduced by up to 28%, whereas the reduction in the low flow index (Q₉₅/Q₅₀) is more dramatic, with up to 100% reduction. Copyright © 2006 John Wiley & Sons, Ltd.     

A framework for assessing flow regime alterations resulting from the effects of climate change and human disturbance

Flow regimes have been severely altered by climate change and human activities in recent decades, which has led to ecological degradation in rivers. This study proposes an analogy analysis-based framework, coupled with the Pettitt test, the indicators of hydrological alteration and the range of variation approach, which were used to distinguish the different effects. This framework was applied to the Sha River, a typical river in North China, to test its effectiveness. The results show that: (i) human disturbance had larger effects on pre-flood flow magnitude, the timing, frequency and duration of high and low pulse, and the flow change rate; (ii) climate change mainly influences the magnitude of flood and post-flood flows, and of extreme events; and (iii) the probability of high alteration from the target frequency increased by 69.7% due to the combined impacts. These results can provide valuable references for water resource and aquatic ecosystem management.     

Classification of natural flow regimes in Iran to support environmental flow management

Abstract

Development of environmental flow standards at the regional scale has been proposed as a means to manage the influence of hydrological alterations on riverine ecosystems in view of the rapid pace of global water resources management. Flow regime classification forms a critical part in such environmental flow assessments. We present a national-scale classification of hydrological regimes for Iran based on a set of hydrological metrics. It describes ecologically relevant characteristics of the natural hydrological regime derived from 15- to 47-year-long records of daily mean discharge data for 539 streamgauges within a 47-year period. The classification was undertaken using a fuzzy partitional method within Bayesian mixture modelling. The analysis resulted in 12 classes of distinctive flow regime types that differ in various hydrological aspects. This classification is being used for further research in regional-scale environmental flow studies in Iran.

Editor D. Koutsoyiannis     

The influence of hydroelectrical development on the flow regime of the karstic river Cetina

The Cetina River is a typical karst watercourse in the deep and well‐developed Dinaric karst. The total length of the Cetina River open streamflow from its spring to the mouth is about 105 km. Estimated mean annual rainfall is 1380 mm. The Cetina catchment is built of Triassic, Jurassic, and Cretaceous carbonate strata. The western part of the catchment by the Cetina River is referred to as the ‘direct’ or topographic catchment. It was defined based on surface morphologic forms, by connection between mountain chain peaks. This part of the catchment is almost entirely situated in the Republic of Croatia. The eastern part of the catchment is referred to as the ‘indirect’ catchment, and is mainly situated in Bosnia‐Herzegovina. Water from the ‘indirect’ catchment emerges from the western ‘direct’ catchment in numerous permanent and temporary karst springs. Since 1960, numerous hydrotechnical works have been carried out on the Cetina River and within its catchment. Five hydroelectric power plants (HEPPs), five reservoirs, and three long tunnels and pipelines have been built. Their operation has significantly altered the natural hydrological regime. The Cetina River is divided into two hydrological reaches. In the 65 km upstream, the hydrological regime was redistributed within the year: low flows had increased and high flows had decreased, although the mean annual discharge remained the same. Part of the Cetina watercourse downstream from the Pran?evi?i Reservoir lost the majority of its flow. The mean annual discharges dropped from 100 m³ s^?1 to less than 10 m³ s^?1 because of the Zaku?ac HEPP development. Copyright © 2003 John Wiley & Sons, Ltd.     

A framework to assess the cumulative impacts of dams on hydrological regime: A case study of the Yangtze River

Comparisons of flow time series between preimpact and postimpact periods have been widely used to determine hydrological alterations caused by reservoir operation. However, preimpact and postimpact periods might also be characterized by different climatological properties, a problem that has not been well addressed. In this study, we propose a framework to assess the cumulative impact of dams on hydrological regime over time. The impacts of the Three Gorges Dam (TGD) on the flow regime of the Yangtze River were investigated using this framework. We reconstructed the unregulated flow series to compare with the regulated flow series during the same period (2010 to 2015). Eco‐surplus and eco‐deficit and the Indicators of Hydrologic Alteration (IHA) parameters were used to examine hydrological regime change. Among 32 IHA parameters, Wilcoxon signed‐rank test and principal component analysis identified the October median flow, 1‐ and 3‐day maximum flows, 1‐day minimum flow, and rise rate as representative indicators of hydrological alterations. Eco‐surplus and eco‐deficit showed that the reservoir also changed the seasonal regime of the flows by reducing autumn flow and increasing winter flow. Changes in annual extreme flows and October flows lead to negative ecological implications downstream of the TGD. Ecological considerations should be taken into account during operation of the TGD in order to mitigate the negative effects on the fluvial ecosystem in the middle reach of Yangtze River. The framework proposed here could be a robust method to assess the cumulative impacts of reservoir operation over time.     

Analysis of the impact of conservation measures on stream flow regime in catchments of the Loess Plateau,China

Catchments in the Loess Plateau have been under the influence of human activities for centuries. In the last four decades, soil conservation measures have accelerated and intensified. These measures were designed to reduce soil erosion, improve agricultural productivity, and enhance environmental quality. It is important to evaluate the effects of these measures on hydrology in order to develop sustainable catchment management plans in the region. This study evaluated changes in stream flow data for four selected catchments in the Loess Plateau following large‐scale soil conservation measures. The non‐parametric Mann–Kendall test was used to identify trends in annual stream flow and the results showed significant downward trends in three of the four catchments. The Pettitt test indicated that a change point occurred in 1978 in these three catchments. Annual precipitation in all the catchments showed no significant trend during the period of record. Comparison of daily flow duration curves for two 20‐year periods (1957–1978) and (1979–2003) showed significant changes in stream flow regime. Reduction in most percentile flows varied between 20 and 45%, and the reduction in low flows was greatest. Overall, the reductions in daily flow were increasing with time, with significant changes occurring in the 1990s. However, it is not clear whether these catchments have seen the full effects of the soil conservation measures, so the results of this study might underestimate the final impact of soil conservation on stream flow regime. Copyright © 2007 John Wiley & Sons, Ltd.     

A simple model of hillslope response for overland flow generation

This paper deals with the derivation of the hydrological response of a hillslope on the assumption of quick runoff by surface runoff generation. By using the simple non‐linear storage based model, first proposed by Horton, an analytical solution of the overland flow equations over a plane hillslope was derived. This solution establishes a generalization for different flow regimes of Horton's original solution, which is valid for the transitional flow regime only. The solution proposed was compared successfully with that of Horton and, for the turbulent flow regime, to the one derived from kinematic wave theory. This solution can be applied easily to both stationary and non‐stationary rainfall excess events. An analytical solution for the instantaneous response function (IRF) was also derived. Finally, simple expressions to compute peak and time to peak of IRF are proposed. Copyright © 2001 John Wiley & Sons, Ltd.     

River flow regime and snow cover of the Pamir Alay (Central Asia) in a changing climate

Abstract

The Vakhsh and Pyandj rivers, main tributaries of the Amu Darya River in the mountainous region of the Pamir Alay, play an important role in the water resources of the Aral Sea basin (Central Asia). In this region, the glaciers and snow cover significantly influence the water cycle and flow regime, which could be strongly modified by climate change. The present study, part of a project funded by the European Commission, analyses the hydrological situation in six benchmark basins covering areas of between 1800 and 8400 km², essentially located in Tajikistan, with a variety of topographical situations, precipitation amounts and glacierized areas. Four types of parameter are discussed: temperature, glaciation, snow cover and river flows. The study is based mainly on a long-time series that ended in the 1990s (with the collapse of the Soviet Union) and on field observations and data collection. In addition, a short, more recent period (May 2000 to May 2002) was examined to better understand the role of snow cover, using scarce monitored data and satellite information. The results confirm the overall homogeneous trend of temperature increase in the mountain range and its impacts on the surface water regime. Concerning the snow cover, significant differences are noted in the location, elevation, orientation and morphology of snow cover in the respective basins. The changes in the river flow regime are regulated by the combination of the snow cover dynamics and the increasing trend of the air temperature.

Editor Z.W. Kundzewicz     

Assessing the effects of the Three Gorges Dam and upstream inflow change on the downstream flow regime during different operation periods of the dam

As the largest hydroelectric dam in the world, the Three Gorges Dam (TGD) has raised wide concerns over the environmental and ecological impacts since its dramatic effect on the downstream flow regime of the Yangtze River. Since 2003, the TGD has progressed from the initial operation period to the full operation period, with different effects on the downstream flow regime over each period. Although the upstream inflow change (USIC) of the TGD is a possibly additional factor affecting the downstream flow regime, this has drawn little attention. This study aims to quantify the individual contributions of the TGD and the USIC to the changes of the downstream flow regime over different operation periods of the dam. Using the Muskingum routing model and the Xin'anjiang rainfall–run‐off model, we reconstruct the discharge unregulated by the TGD for the post‐TGD period from 2003 to 2015. On this basis, the effects of the TGD and the USIC on the downstream flow regime are quantitatively assessed. Benchmarked against the flow regime during the pre‐TGD period from 1955 to 2002, it is found that the TGD and the USIC play considerable and comparable roles in affecting the downstream flow regime during the whole post‐TGD period from 2003 to 2015. Furthermore, the TGD appears to have a limited effect on the downstream flow regime during the initial operation period from 2003 to 2008 relative to the USIC. In contrast, during the full operation period from 2009 to 2015, the TGD plays a dominant role in changing the downstream flow regime, although the effect of the USIC cannot be neglected. The findings of this study are helpful to understand the exact impacts of the TGD on the downstream flow regime, thereby facilitating the development of a rational strategy for operating the dam.     

Assessment of the impact of climate change on the flow regime of the Han River basin using indicators of hydrologic alteration

Most natural disasters are caused by water‐/climate‐related hazards, such as floods, droughts, typhoons, and landslides. In the last few years, great attention has been paid to climate change, and especially the impact of climate change on water resources and the natural disasters that have been an important issue in many countries. As climate change increases the frequency and intensity of extreme rainfall, the number of water‐related disasters is expected to rise. In this regard, this study intends to analyse the changes in extreme weather events and the associated flow regime in both the past and the future. Given trend analysis, spatially coherent and statistically significant changes in the extreme events of temperature and rainfall were identified. A weather generator based on the non‐stationary Markov chain model was applied to produce a daily climate change scenario for the Han River basin for a period of 2001–2090. The weather generator mainly utilizes the climate change SRES A2 scenario driven by input from the regional climate model. Following this, the SLURP model, which is a semi‐distributed hydrological model, was applied to produce a long‐term daily runoff ensemble series. Finally, the indicator of hydrologic alteration was applied to carry out a quantitative analysis and assessment of the impact of climate change on runoff, the river flow regime, and the aquatic ecosystem. It was found that the runoff is expected to decrease in May and July, while no significant changes occur in June. In comparison with historical evidence, the runoff is expected to increase from August to April. A remarkable increase, which is about 40%, in runoff was identified in September. The amount of the minimum discharge over various durations tended to increase when compared to the present hydrological condition. A detailed comparison for discharge and its associated characteristics was discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Response of the hydrological regime of the Yellow River to the changing monsoon intensity and human activity

Abstract

In the past 50 years, influenced by global climate change, the East Asian summer monsoon intensity (SMI) changed significantly, leading to a response by the water cycle of the Yellow River basin. The variation in SMI has three stages: (1) 1951–1963, SMI increased; (2) 1963–1965, SMI declined sharply, a feature that may be regarded as an abrupt change; and (3) 1965–2000, SMI remained at low levels and showed a tendency to decline slowly. The decreased SMI led to a reduction in water vapour transfer from the ocean to the Yellow River basin, and thus precipitation decreased and the natural river runoff of the Yellow River also decreased. Due to the increase in population and therefore in irrigated land area, the ratio of net water diversion to natural river runoff increased continuously. Comparison of the ratio of net water diversion to natural river runoff before and after the abrupt change in SMI indicates some discontinuity in the response of the man-induced lateral branch of the water cycle to the abrupt change in SMI. The frequently occurring flow desiccation in the lower Yellow River can be regarded as a response of the water cycle system to the decreasing summer monsoon intensity and increasing population. When the ratio of net water diversion exceeded the ratio of natural runoff of the low-flow season to the annual total natural runoff, flow desiccation in the lower Yellow River would occur. When the ratio of net water diversion is 0.3 larger than the ratio of the natural runoff of the low-flow season to the annual total natural runoff, an abrupt increase in the number of flow desiccation events is likely to occur.     

福建山美水库浮游动物群落结构时空特征及其影响因子分析

山美水库既是福建省泉州市饮用水源地,也肩负着为台湾省金门县供水的功能,但春夏季过高的pH值影响了水库水质.为此,从2020年起,调整水库鱼类放养结构和捕捞策略,并研究鱼类群落调控后山美水库浮游动物群落结构的响应及其与环境因子的关系.本研究于2020年和2021年连续两年的1月（冬季）、4月（春季）、7月（夏季）、10月（秋季）调查山美水库21个采样点的浮游动物群落结构和水环境因子.结果共鉴定出浮游动物68属102种,其中轮虫21属41种（40.20%）,原生动物32属41种（40.20%）,枝角类8属13种（12.75%）,桡足类7属7种（6.86%）.2020—2021年山美水库浮游动物平均密度为（1443.05±360.02） ind./L,平均生物量为（1.21±0.27） mg/L,2021年浮游动物密度和生物量显著高于2020年,其中,2021年枝角类和桡足类的密度分别显著高于2020年枝角类和桡足类的密度,2021年库首、库中和库尾区域枝角类生物量显著高于2020年对应区域;2021年桡足类生物量显著高于2020年.春冬季浮游动物群落的优势种主要为原生动物,夏秋季浮游动物群落的优势种主要为轮虫.根据浮游动物密度和生物量评价水体营养状态,夏季山美水库处于中营养状态,春、秋和冬季处于贫营养状态.影响浮游动物群落结构分布的主要环境因子为电导率、水温、溶解氧、硝态氮、透明度和高锰酸盐指数.研究表明调整鱼类放养和捕捞措施提高了浮游动物密度和生物量,基于此提出了通过调整鱼类群落结构改变浮游动物群落结构,进而改善水环境的建议,可为湖泊水库水环境保护和水生生物资源高效利用提供科学依据.     

Inter-catchment comparison of flow regime between the Hailiutu and Huangfuchuan rivers in the semi-arid Erdos Plateau,Northwest China

Abstract

Two river catchments, the Huangfuchuan and the Hailiutu, located in the same climate zone in the Erdos Plateau, China, have distinctly different flow regimes. This study systematically compared differences between the flow regimes of these two catchments using several statistical methods, and analysed the possible causes. The variations in yearly, monthly and daily mean discharges were found to be much greater in the Huangfuchuan catchment than in the Hailiutu catchment. Preliminary analysis indicated that these differences are not caused by changes in climate, but are instead attributable to differences in geology, geomorphology, hydrological processes and human interventions. In the Hailiutu catchment, the dominant groundwater contribution maintains stationary daily and monthly river discharges, while shifts in yearly mean discharges were closely associated with the expansion or reduction of crop area. In the Huangfuchuan catchment, the dominant direct rainfall–runoff process generates flashier daily and monthly river discharges, while the decrease of yearly mean discharges is caused mainly by the construction of check dams. These findings have significant implications for water resource management and the implementation of proper soil and water conservation measures in the middle reach of the Yellow River Basin of China.

Editor Z.W. Kundzewicz; Associate editor Y. Gyasi-Agyei     

Spatial and temporal variability of the hydrological response in a small Mediterranean research catchment (Vallcebre,Eastern Pyrenees)

This paper analyses the spatial and temporal variability of the hydrological response in a small Mediterranean catchment (Cal Rodó). The first part of the analysis focuses on the rainfall–runoff relationship at seasonal and monthly scale, using an 8‐year data set. Then, using storm‐flow volume and coefficient, the temporal variability of the rainfall–runoff relationship and its relationship with several hydrological variables are analysed at the event scale from hydrographs observed over a 3‐year period. Finally, the spatial non‐linearity of the hydrological response is examined by comparing the Cal Rodó hydrological response with the Can Vila sub‐catchment response at the event scale. Results show that, on a seasonal and monthly scale, there is no simple relationship between rainfall and runoff depths, and that evapotranspiration is a factor that introduced some non‐linearity in the rainfall–runoff relationship. The analysis of monthly values also reveals the existence of a threshold in the relationship between rainfall and runoff depths, denoting a more contrasted hydrological response than the one usually observed in humid catchments. At the event scale, the storm‐flow coefficient has a clear seasonal pattern with an alternance between a wet period, when the catchment is hydrologically responsive, and a dry summer period, when the catchment is much less reactive to any rainfall. The relationship between the storm‐flow coefficient and rainfall depth, rainfall maximum intensity and base‐flow shows that observed correlations are the same as those observed for humid conditions, even if correlation coefficients are notably lower. Comparison with the Can Vila sub‐catchment highlights the spatial heterogeneity of the rainfall‐runoff relationship at the small catchment scale. Although interpretation in terms of runoff processes remains delicate, heterogeneities between the two catchments seem to be related to changes in the ratio between infiltration excess and saturation processes in runoff formation. Copyright © 2007 John Wiley & Sons, Ltd.     

The relative impacts of climate change and urbanization on the hydrological response of a Korean urban watershed

We assessed the relative hydrological impacts of climate change and urbanization using an integrated approach that links the statistical downscaling model (SDSM), the Hydrological Simulation Program—Fortran (HSPF) and the impervious cover model (ICM). A case study of the Anyangcheon watershed, a representative urban region in Korea, illustrates how the proposed framework can be used to analyse the impacts of climate change and urbanization on water quantity and quality. The evaluation criteria were measurements of low flow (99, 95, and 90 percentile flow), high flow (10, 5, and 1 percentile value), pollutant concentration (30, 10, and 1 percentile value), and the numbers of days required to satisfy the target water quantity and quality for a sensitive comparison of subtle impacts of variations in these measures. Nine scenarios, including three climate scenarios (present conditions, A1B, and A2) and three land use change scenarios, were analysed using the HSPF model. The impacts of climate change on low flow (34·1–59·8% increase) and high flow (29·1–37·1% increase) were found to be much greater than those on the biochemical oxygen demand (BOD) (3·8–10·0% decrease). On the other hand, the impacts of urbanization on water quality (19·0–44·6% increase) are more significant than those on high (1·0–4·4% increase) and low flow (11·4–25·6% decrease). Furthermore, low flows are more sensitive to urbanization than high flows. The number of days required to satisfy the target water quantity and quality can be a sensitive criterion to compare the subtle impacts of climate and urbanization on human society, especially as they are much more sensitive than low flow and pollutant concentration. Finally, urbanization has a potent impact on BOD while climate change has a high impact on flow rate. Therefore, the impacts of both climate change and urbanization must be included in watershed management and water resources planning for sustainable development. Copyright © 2010 John Wiley & Sons, Ltd.     

细菌群落组成对微囊藻水华分解过程的响应

为探究细菌群落组成对微囊藻水华腐败分解过程的响应,在太湖梅梁湾沿岸进行为期11 d的原位围隔实验,模拟蓝藻水华聚集分解过程,并监测了此过程中水体环境因子和细菌群落组成.结果表明,水体理化因子和细菌群落组成在微囊藻水华分解的过程中发生了显著变化.冗余分析显示细菌的群落组成与水体氧化还原环境(溶解氧或氧化还原电位)、pH值、浮游植物生物量和营养盐浓度(总磷、硝态氮浓度)密切相关.研究还发现了某些与微囊藻水华分解密切相关的特殊细菌类群,其中隶属于黄杆菌科(拟杆菌门)的一个类群在微囊藻厌氧分解的阶段占据显著优势,其功能有待于进一步研究.