Changes In Hydrological Characteristics Research Articles

Assessing future urban flood hazard: A comprehensive approach to estimating the implications of future rainfall scenarios

AbstractEstimating potential changes in future flood patterns based on anticipated changes in hydrological characteristics within the basin is crucial for mitigating flood damage and managing flood risk. In this study, nonparametric probability models are used to estimate future rainfall patterns in Seoul under the GCM‐based climate change scenarios (CCS), and the estimated future daily rainfall data was temporally downscaled to hourly units using the KNNR‐GA technique. Changes in flood hazard and runoff characteristics of the target area based on the estimated future rainfall data are quantitatively assessed. The results highlight that under CCS, flood runoff may increase further into the future, resulting in more significant changes in flood patterns and accelerating the increase in flood hazard. The delta change factor of flood risk indicators increased relatively significantly in more severe CCS. This study also proposed a process to estimate future flood runoff and mitigation effects according to CCS by reflecting various flood mitigation measures in the urban drainage system model. These findings can offer valuable insights for setting the direction of current and future mitigation measures.

The effect of planting grass filter strips on fishes in agricultural headwater streams

Abstract Grass filter strips (i.e., herbaceous riparian buffers) are a widely used conservation practice in the United States to mitigate the impacts of agriculture on streams and rivers. Yet, only a limited amount of information is available on the effects of grass filter strips on stream fishes and instream habitat conditions and long‐term assessments are rare. The objective of this research was to document the long‐term effects of planting grass filter strips adjacent to channelized agricultural headwater streams on fish community structure and instream habitat. Fishes, instream habitat and riparian characteristics were sampled from three channelized agricultural headwater streams without grass filter strips, three channelized agricultural headwater streams with grass filter strips and two unchannelized streams having forested riparian habitats in central Ohio from spring of 2006 to autumn of 2015. Fish species richness, abundance, darter species richness, per cent darters, sunfish species richness, minnow species richness and per cent headwater fishes did not differ among riparian habitat types. Darter species richness and per cent darters differed annually. Mean water depth, velocity, wetted width, instream habitat diversity, dominant grain size and per cent instream wood did not differ among riparian habitat types. Mean water depth, water velocity, wetted width and instream habitat diversity exhibited annual differences. Additionally, mean riparian width, woody vegetation density and per cent canopy cover were greater in forested streams than the unplanted and grass filter strip streams. Riparian characteristics did not differ annually. The lack of fish community responses 10–13 years after planting grass filter strips is probably due to the lack of corresponding changes in hydrological characteristics, substrate and instream wood amounts. These results suggest that grass filter strips should not be implemented alone but in conjunction with conservation practices that will improve physical habitat quality and water quality.

Prediction of Changes in Land Use/Land Cover and Hydrological Response in the Upper Ciliwung Watershed

As a result of rapid urbanization, in 2021, it was recorded that the forest area in the Upper Ciliwung Watershed was only a quarter of the total area. Therefore, the Upper Ciliwung Watershed cannot optimally perform its hydrological functions. One of the reasons for conducting this research is to provide consideration in calculating the adequacy of the forest area in the Upper Ciliwung watershed. In addition, this research was also conducted to estimate the discharge and volume of water, the trend of land use change in the Upper Ciliwung watershed in the last few decades, what might happen in the future if land use change continues, and how much influence it will have in maintaining forest areas that exist in minimizing the risk of future disasters occurring due to the high rate of development. This study combines remote sensing technology and hydrological modelling to understand changes in hydrological characteristics when LULC transformed from 2001 to 2051. The spatial-temporal dynamics of LULC and its hydrological response were estimated using an integrated approach that combines remote sensing, Cellular Automata-Markov Chain based on Multi-Layer Perceptron with an HEC-HMS modelling system. Multitemporal satellite imagery is used to understand LULC changes and projections for 2031 and 2051 in the Upper Ciliwung watershed. The analysis shows that there has been a very significant increase in the developed area over the years. In contrast, other types of LULC have decreased. In 2001-2051, the forest area experienced the worst decline, 22,423,493 m2. Meanwhile, the developed area experienced a significant increase of 49,771,952 m2. This changing pattern has a negative impact on hydrological characteristics. Hydrological modelling shows that the volume and discharge are projected to increase drastically to reach 258.61 x 106 m3 and 26.3 m3/s, respectively, in 2051.

The Impact of Flooding on Snail Spread: The Case of Endemic Schistosomiasis Areas in Jiangxi Province, China.

Flooding is the main natural factor in snail diffusion, and it has a negative impact on schistosomiasis transmission. There are few studies on the spread and migration of snails following a flood; therefore, we aimed to investigate the influence of flooding on snail diffusion and explore the characteristics and laws of snail diffusion in Jiangxi Province. By using a retrospective survey and cross-sectional survey, the data on snail spreading in Jiangxi Province from 2017 to 2021 were collected. The distribution, nature, and area of snail spread were systematically analyzed in combination with the hydrological situation, types of region, and types of flood. From 2017 to 2021, a total of 120 snail-spread environments were found, including in 92 hilly areas and in 28 lake areas. The areas caused by flood and by other means numbered 6 and 114, respectively. The proportions of recurrence, expansion, and first-time occurrences were 43.42%, 38.16%, and 18.42%, respectively, and the 14 new snail environments were only distributed in the hilly areas. With the exception of 2018, the ratio of snail-spread areas in the hilly region was higher than that in lake region in other years. The average density of live snails was 0.0184-1.6617 no./0.1 m2 and 0.0028-0.2182 no./0.1 m2 in the hilly region. Among the 114 environments affected by floods, 86 consisted of hilly environments, including 66 spreading environments affected by rainstorm floods, and 20 rainstorm debris flow environments. There were 28 lake areas, of which 10 were in the Jiangxi section of Yangtze River and were affected by rainstorm floods. Snail spread following flooding has a certain 'lag effect,' and = simple annual changes in hydrological characteristics have little effect on the diffusion of snails or on their density = in the affected environment, but it is more closely related to local floods. The hilly environments are more susceptible to floods than the lake region, and the risk of snail spread is much higher in the hilly than in the lake region.

Assessment of hydro-morpho dynamics of the Nile River confluence scour

ABSTRACT Confluences of rivers are important component of river systems. Confluence scour is significant geomorphologically because it is a node in a channel network that controls sediment distribution, thus controlling the formation of channel migration. Nile River confluences take various shapes, such as downstream islands. Due to the construction of Aswan High Dam, major changes in hydrological characteristics downstream of the dam have affected river morphology, including the formation of islands. The purpose of this study is to investigate the hydrodynamic and morphological parameters for the Nile River confluences to provide an appropriate formula to predict confluence scour depth. For the current study, six confluence areas were selected. A numerical model was used to calculate the hydraulic characteristics of the Nile River. Geometric, morphological, and hydrodynamic analyses of selected confluences were performed in different years. Five confluence scour equations were applied to compute scour depths for the selected confluences. The scour depths for the specified confluences were calculated using five confluence scour equations. Field observations were compared to the calculated scour depths. The selected confluence scour equations didn’t have a satisfying performance for estimating the confluence scour depth in the Nile River. A new dimensionless confluence scour equation has been established.

Temporal disaggregation of hourly precipitation under changing climate over the Southeast United States

Climate change impacts on precipitation characteristics will alter the hydrologic characteristics, such as peak flows, time to peak, and erosion potential of watersheds. However, many of the currently available climate change datasets are provided at temporal and spatial resolutions that are inadequate to quantify projected changes in hydrologic characteristics of a watershed. Therefore, it is critical to temporally disaggregate coarse-resolution precipitation data to finer resolutions for studies sensitive to precipitation characteristics. In this study, we generated novel 15-minute precipitation datasets from hourly precipitation datasets obtained from five NA-CORDEX downscaled climate models under RCP 8.5 scenario for the historical (1970–1999) and projected (2030–2059) years over the Southeast United States using a modified version of the stochastic method. The results showed conservation of mass of the precipitation inputs. Furthermore, the probability of zero precipitation, variance of precipitation, and maximum precipitation in the disaggregated data matched well with the observed precipitation characteristics. The generated 15-minute precipitation data can be used in all scientific studies that require precipitation data at that resolution.

KAJIAN MORPHOMETRI PADA SATUAN WILAYAH PENGELOLAAN DAS PRIORITAS DI KOTA PADANG (STUDI KASUS PADA DAS ARAU, DAS KURANJI, DAN DAS AIR DINGIN)

In line with the sustainable development process, it is necessary to regulate activities with the main priority to re-create the ecological balance of the environment. The three rivers which were expected to receive rainfall, such as Batang Kuranji, Batang Arau and Batang Air Dingin, were unable to cope with the flooding. The hydrological conditions of the 3 watersheds are currently experiencing changes in hydrological characteristics which are marked by increased flood potential. This threat, apart from natural factors such as climate and extreme rainfall, can also occur due to human factors such as cultivating floodplain areas, land allocations in flood plains that are not in accordance with land functions. Changes in land use in an area can affect the function of the water system. This is in accordance with the opinion of Arsyad (2010), which states that any treatment given to a plot of land can affect the water system in that place and places downstream. From the above threat parameters, flooding is also strongly influenced by natural phenomena in the form of morphometry consisting of watershed area, watershed shape, river network, flow density, flow pattern, land use and river steepness gradient. For this reason, research on watershed morphometry needs to be carried out so that the causes of flooding in the watershed can be identified. Floods that occurred from 2016 to 2021, have harmed the community. By using Paimin's theory for morphometry, the ARC GIS program to determine the extent of flooding, as well as Thiessen's theory to determine rainfall and a rational theory to analyze discharge, it was obtained into 3, namely the Arau watershed, Kuranji watershed and Air Dingin watershed prone to flooding with the highest score due to the use of land.

Prediction of Aquatic Ecosystem Health Indices through Machine Learning Models Using the WGAN-Based Data Augmentation Method

Changes in hydrological characteristics and increases in various pollutant loadings due to rapid climate change and urbanization have a significant impact on the deterioration of aquatic ecosystem health (AEH). Therefore, it is important to effectively evaluate the AEH in advance and establish appropriate strategic plans. Recently, machine learning (ML) models have been widely used to solve hydrological and environmental problems in various fields. However, in general, collecting sufficient data for ML training is time-consuming and labor-intensive. Especially in classification problems, data imbalance can lead to erroneous prediction results of ML models. In this study, we proposed a method to solve the data imbalance problem through data augmentation based on Wasserstein Generative Adversarial Network (WGAN) and to efficiently predict the grades (from A to E grades) of AEH indices (i.e., Benthic Macroinvertebrate Index (BMI), Trophic Diatom Index (TDI), Fish Assessment Index (FAI)) through the ML models. Raw datasets for the AEH indices composed of various physicochemical factors (i.e., WT, DO, BOD5, SS, TN, TP, and Flow) and AEH grades were built and augmented through the WGAN. The performance of each ML model was evaluated through a 10-fold cross-validation (CV), and the performances of the ML models trained on the raw and WGAN-based training sets were compared and analyzed through AEH grade prediction on the test sets. The results showed that the ML models trained on the WGAN-based training set had an average F1-score for grades of each AEH index of 0.9 or greater for the test set, which was superior to the models trained on the raw training set (fewer data compared to other datasets) only. Through the above results, it was confirmed that by using the dataset augmented through WGAN, the ML model can yield better AEH grade predictive performance compared to the model trained on limited datasets; this approach reduces the effort needed for actual data collection from rivers which requires enormous time and cost. In the future, the results of this study can be used as basic data to construct big data of aquatic ecosystems, needed to efficiently evaluate and predict AEH in rivers based on the ML models.

СРАВНИТЕЛЬНАЯ ОЦЕНКА ФОРМИРОВАНИЯ СТОКА РЕК В КЛИМАТИЧЕСКИХ ЗОНАХ ГОРНОГО ПАМИРА

The research object. The hydrological characteristics of the Gunt and Vanch rivers belonging to the Southwestern and Central climatic zones of the Pamirs and are tributaries of the transboundary Pyanj River are considered. Long-term average values of temperature and precipitation as the main factors affecting the formation of river flows are determined for the period 1944–2016. The state of glaciation in the basins of the respective rivers is estimated. Goal. A comparative assessment of the influence of climatic features and mountain orography on the formation of river flows. Determination of the trend of changes in the climatic conditions of the Gunt and Vanch river basins at different periods of more than 70 years (1944–2016). Research methods. Generalization, systematization of meteorological and hydrological characteristics and determination of their change compared with the base period 1960–1990. Statistical processing of meteorological and hydrological data and establishing a trend of changes in climatic and hydrological characteristics using a differentiated method. Research results. It is shown that the nature of changes in hydrological characteristics, namely the flow of rivers in different climatic zones of the Pamir can differ significantly. On the example of two rivers (Gunt and Vanch) - tributaries of the transboundary Pyanj river, it is shown that the trend of change in the flow of the Gunt river differs from the Vanch river due to the state of glaciation of the river basin. To explain the results the meteorological conditions of the respective river basins and their possible impact on river hydrology were studied. Conclusion. The hydrological characteristics of the Gunt and Vanch rivers in the Pamirs taking into account the meteorological conditions of the respective river basins show that a key factor in improving the state of glaciation and reducing degradation processes, as well as achieving positive trends in the mass balance of glaciers is the presence of sufficient air mass in the glaciation zone. Naturally, this is the key to ensuring a sufficient amount of runoff.

Estimation of the Future Probable Precipitation based on the Assumption of Non-Stationarity in Seoul

In this study, an estimation of the future probable rainfall in Seoul, Korea, was performed, using non-stationary frequency analysis according to climate change and it was compared with the current probable rainfall. Hourly rainfall data provided by the Korea Meteorological Administration with durations of 1, 2, 3, 6, 12, 24, and 48-h were used as input. For the future projection of precipitation, the RCP 8.5 scenario was selected with the same durations. Moreover, the future hourly rainfall was extracted from using the daily precipitation from 29 Global Climate Models (GCMs), based on the statistical temporal down-scaling method and their corresponding bias corrections. Subsequently, the annual maximum precipitation was extracted for each year. In this study, both stationary and non-stationary frequency analysis was applied based on the observed and predicted time series data sets. In particular, for the non-stationary frequency analysis, the Differential Evolution Markov Chain technique, which combines the Bayesian-based Differential Evolution and Markov chain Monte Carlo methods, was adopted. Finally, the current and future intensity-duration-frequency curves were derived from the optimal probability distribution, and each probable rainfall was estimated. The results of the 29-scenario are presented with quantile estimations. The non-stationary frequency analysis results for Seoul revealed rainfalls of 94.4 mm/h for 30 y, 101.7 mm/h for 50 y, and 111.5 mm/h for 100 y return periods. The average value of the 29-GCM model ensemble was estimated to be approximately 5 mm/h higher than that obtained from the stationary frequency analysis. Considering the changes in hydrological characteristics due to climate change in Seoul, the results of this study could be utilized to pro-actively respond to natural disasters due to such phenomena.

Changes in the hydrological characteristics of Cauvery river draining the eastern side of southern Western Ghats, India

ABSTRACTThe changes in land use and regional climate together with human interventions affect the hydrological processes, resulting in the spatial and temporal alterations of surface and subsurface flow processes. Both climate and land surface change have adverse implications on the natural hydrological system in terms of variation in the run-off regime, surface storage, evapotranspiration, subsurface flow and infiltration, thereby affecting the hydrology of the river basin as a whole. Even though several studies worldwide have attempted to address the influence of climate change, land-use change and human activities on the hydrology of river basins, either as a whole or limited to a few components of the hydrological cycle, limited attention has been given to study the hydrological changes in the river basins of arid and semi-arid tropics, which are essentially fed by precipitation. The objective of the study is to analyse the changes in hydrological characteristics of the Cauvery river basin, a semi-arid river basin in South India. The changes in the hydrology of the Cauvery river basin are studied by analysing the trends in hydro-meteorological parameters using Mann-Kendall trend tests and Sen’s estimator of the slope. The results showed that the changes in the volume of rainfall and the number of rainy days significantly affect the overall hydrological regime of the river basin. The analysis of annual and seasonal rainfall over the Cauvery river basin showed a decreasing trend in the middle Cauvery basin. A declining trend in the number of rainfall events was also observed in the middle Cauvery region. The effect of decreasing trend in the volume of rainfall and number of rainy days is evident from the decreasing trends in the streamflow of the main channel and tributaries of the Cauvery river. The regions of increase in evapotranspiration showed a significant correlation with the regions which exhibited a decline in groundwater level.

Climate indicators of changes in hydrological characteristics (a case of the Psyol river basin)

Formulation of the problem. A national climate program, complying with the Association Agreement between Ukraine and the EU, is aimed at long-term adaptation measures to climate change, providing for the development of legislation in the field of environmental protection, sectoral strategies, improving air and water quality. These measures require identification of climatic factors’ impact on hydrological characteristics of water bodies in any area in order to protect and improve them, as well as a comprehensive approach to the rational management of water resources. Analysis of previous research. Using mathematical models of atmospheric circulation allows us to obtain generalized calculations of the average global and regional air temperature, characterized by significant errors in case of different models. Problems of further research. Modern changes in climatic conditions in Ukraine are characterized by locality and rapidity: increasing number of anomalous atmospheric phenomena, frequency of droughts, dry winds which, according to preliminary estimates, may lead to reduction of water resources, changes in internal annual redistribution of water temperature and runoff against the background of increasing thermal resources of the territory. The purpose. The article analyses climatic indicators’ influence on the main hydrological characteristics on the example of the Psyol river basin within Ukraine. Research methods. Research methods are presented by statistical and cartographic analysis (correlation analysis method). The initial information is the results of observations contained in the State Climate Cadastre and the State Water Cadastre for the Dnieper Valley. Presentation of the main research material. Analysis of climate change in the Psyol river basin indicates a decrease in water consumption, both in the main river of the basin and in its main tributaries. In addition to changes in temperature and humidity, the reasons for this process were the shifts that occurred in the nature of the intra-annual distribution of the runoff. During the late XX – early XXI century the share of spring floods decreased due to the reduced period of ice phenomena and corresponding decrease in the thickness of the snow cover on the rivers. As a result, the most important component of the annual runoff of rivers began to decrease rapidly. The role of groundwater in the formation of water runoff increased against the background of a predominant decrease in precipitation. This is especially true for medium-size and small rivers, subject to significant anthropogenic pressure: over-regulation of channels, creation of artificial lakes, their shallowing. Practical value. Based on the main provisions of the national environmental policy of Ukraine on the use of water resources and the implementation of European principles of the Water Framework Directive 2000/60 / EC (ERVD) the study of changes in hydrological regime of rivers is of practical importance for sustainable management. Research results. The study of the impact of changes in climatic indicators on hydrological characteristics makes it possible to determine the reference conditions and classes of ecological status of rivers under conditions of anthropogenic pressure against the background of further changes in climatic indicators that will have different trends.

Spatiotemporal changes in the ecological status of water bodies on the mining territories of the Syunik Province (Republic of Armenia)

We discuss the changes in hydrological characteristics of water bodies caused by freshwater withdrawals to meet the interests of various users on the territory of the Syunik Province of the Republic of Armenia. An analysis is made of the possibilities of combining the water withdrawal for mining enterprises and for agriculture. The problems with water supply of settlements located on this territory are highlighted. The temporal dynamics of water withdrawals is presented for separate rivers as well as its relationship with the minimum and ecological flow. It is found that the anthropogenic load on water bodies is more clearly pronounced in the case of a degradation of the quality of water resources as a result of the industrial waste water diversion, and wash-out of pollutants from the territory of enterprises during floods and in the case of emergency input of wastes from tailings pools, rock spoil heaps and waste storage areas. Results of these authors’ observations, data of routine observations and material from published sources were used in analyzing the water quality in the rivers of the Syunik Province. We calculated the coefficients of ecological quality and determined the river water quality classes according to physicochemical and biological indicators. Assessments of the river water quality class were made in accordance with the methodology of Directive 2000/60/EC. We identified the main pollutants that are responsible for the water quality class, and the factors of impact on natural waters governing the ecological status of water bodies. A comprehensive analysis is made of the intensity of anthropogenic impact on surface waters. The ecological status of water bodies is determined. Spatial changes in the quality indicators of the water of the region’s main rivers are demonstrated. Special emphasis is placed on the need to implement immediate measures to improve technological processes and bring the operation of enterprises into compliance with ecological normative standards.

Possible changes in hydrological characteristics due to streamflow control.

Possible changes in hydrological characteristics due to streamflow control.

Empirical assessment of effects of urbanization on event flow hydrology in watersheds of Canada’s Great Lakes-St Lawrence basin

We conducted an empirical hydrological analysis of high-temporal resolution streamflow records for 27 watersheds within 11 river systems in the Greater Toronto Region of the Canadian Great Lakes basin. Our objectives were to model the event-scale flow response of watersheds to urbanization and to test for scale and threshold effects. Watershed areas ranged from 37.5km2 to 806km2 and urban percent land cover ranged from less than 0.1–87.6%. Flow records had a resolution of 15-min increments and were available over a 42-year period, allowing for detailed assessment of changes in event-scale flow response with increasing urban land use during the post-freshet period (May 26 to November 15). Empirical statistical models were developed for flow characteristics including total runoff, runoff coefficient, eightieth and ninety-fifth percentile rising limb event runoff and mean rising limb event acceleration. Changes in some of these runoff metrics began at very low urban land use (<4%). Urban land use had a very strong influence on total runoff and event-scale hydrologic characteristics, with the exception of 80th percentile flows, which had a curvilinear relationship with urban cover. Event flow acceleration increased with increasing urban cover, thus causing 80th percentile runoff depths to be reached sooner. These results indicate the potential for compromised water balance when cumulative changes are considered at the watershed scale. No abrupt or threshold changes in hydrologic characteristics were identified along the urban land use gradient. A positive interaction of urban percent land use and watershed size indicated a scale effect on total runoff. Overall, the results document compromised hydrologic stability attributable to urbanization during a period with no detectable change in rainfall patterns. They also corroborate literature recommendations for spatially distributed low impact urban development techniques; measures would be needed throughout the urbanized area of a watershed to dampen event-scale hydrologic responses to urbanization. Additional research is warranted into event-scale hydrologic trends with urbanization in other regions, in particular rising limb event flow accelerations.

Impact of Climate Change on Streamflow in the Tropical Lowland of Kapuas River, West Borneo, Indonesia

Indonesia is one of the tropical area which its climate is generally experienced of two distinct seasons, rainy season and dry season. However, the beginning and end of each season is not always occurred at the same month on every year. Characteristics of hydrology variables, especially rainfall events, is strongly influenced by local and global climatic conditions. Thus it is important to identify how far the changes of global climate would effect the characteristic of the hydrology variables in a certain watershed. These informations will be valuable to determine the correct measures for the watershed's development and management in the future. Kapuas River, one of rivers in Borneo, Kalimantan-Indonesia, has streamflow which is empirically changed during the last three decades. The changes of hydrological characteristics are analysed statistically based on rainfall data recorded at Supadio Rainfall and Meteorological Station-Pontianak. The monthly rainfall data were available from 1968-2013, while the daily rainfall data were available during 1981-2013. The 1968-2013 data were then used to analyze the trend of annual rainfall, while the 1981-2013 were used to analyze the changes of hydrological characteristics. The results showed that the numbers of average annual rainfall is 3,206mm, while the average monthly rainfall is 267mm. During the 45-year period (1968-2013) the annual rainfall tends to decrease, but for the past 30 years it tends to increase. The number of rainy days during the past 30 years tends to increase. Whereas the rainfall intensity on short duration tends to decrease. Even though the availability of streamflow in the river during the past 30 years tends to decrease. It was proven based on observed streamflow in the tributary of Kapuas, Sekayam River. It was found that during 35 years (1978-2012) the availability of streamflow tends to decrease. It is, therefore can be concluded that hydrological characteristics of lowlands at Kapuas River has changed.

Long-term monitoring programme of the hydrological variability in the Mediterranean Sea: a first overview of the HYDROCHANGES network

Abstract. The long-term monitoring of basic hydrological parameters (temperature and salinity), collected as time series with adequate temporal resolution (i.e. with a sampling interval allowing the resolution of all important timescales) in key places of the Mediterranean Sea (straits and channels, zones of dense water formation, deep parts of the basins), constitute a priority in the context of global changes. This led CIESM (The Mediterranean Science Commission) to support, since 2002, the HYDROCHANGES programme (http//www.ciesm.org/marine/programs/hydrochanges.htm), a network of autonomous conductivity, temperature, and depth (CTD) sensors, deployed on mainly short and easily manageable subsurface moorings, within the core of a certain water mass. The HYDROCHANGES strategy is twofold and develops on different scales. To get information about long-term changes of hydrological characteristics, long time series are needed. But before these series are long enough they allow the detection of links between them at shorter timescales that may provide extremely valuable information about the functioning of the Mediterranean Sea. The aim of this paper is to present the history of the programme and the current set-up of the network (monitored sites, involved groups) as well as to provide for the first time an overview of all the time series collected under the HYDROCHANGES umbrella, discussing the results obtained thanks to the programme.

Possible climatic changes of hydrological regime of valley reservoirs

The paper presents the simulation outputs of changes of hydrological characteristics of reservoirs of different kind (changes in residence time and in water column stratification) in case of forecast warming according to the most adverse scenario for Moscow water supply, when annual flow and springflood flow depth decrease.

Meltwater storage and delaying characteristics of Gangotri Glacier (Indian Himalayas) during ablation season

AbstractHimalayan basins have considerable snow‐ and glacier‐covered areas, which are an important source of water, particularly during summer season. In the Himalayan region, in general, the glacier melt season is considered to be from May to October. Changes in hydrological characteristics of the runoff over the melt season can be understood by studying the variation in time to peak and time lag between melt generation and its emergence as runoff. In the present study, the runoff‐delaying characteristics of Gangotri Glacier, one of the largest glaciers in the Indian Himalayas, have been studied. For this purpose, hourly discharge and temperature data were collected near the snout of the glacier (4000 m) for three ablation seasons (2004–2006). The diurnal variations in discharge and temperature provided useful information on water storage and runoff characteristics of the glacier. In the early stages of the ablation period, poor drainage network and stronger storage characteristics of the glaciers due to the presence of seasonal snow cover resulted in a much delayed response of melt water, providing a higher time lag and time to peak as compared to the peak melt season. A comparison of runoff‐delaying parameters with the discharge ratio clearly indicated that changes in time lag and time to peak are inversely correlated with variations in discharge. Impact of such meltwater storage and delaying characteristics of glaciers on hydropower projects being planned/developed on glacier‐fed streams in India has been discussed. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Root studies on grass species in a semi-arid South Africa along a degradation gradient

Understanding changes in hydrological characteristics of rangeland ecosystems with degradation is essential when making rangeland management decisions in arid and semi-arid areas to ensure sustainable animal production. The impact of rangeland degradation on root production, root/shoot ratio and water-use efficiency was therefore determined for a semi-arid rangeland, over a 7-year period (1999/00 to 2005/06 growing seasons). Water-use efficiency (WUE) is defined as the quantity of above- and/or belowground phytomass produced over a certain period of time per unit of water evapotranspired. Sampling was from rangeland artificially maintained in three different rangeland conditions, viz. good, moderate and poor. As much as 86, 89 and 94% of the roots for rangelands in good, moderate and poor conditions, respectively, occurred at a depth of less than 300 mm. Root mass was strongly seasonal with the most active growth taking place during March and April. Root mass appears to be greater than aboveground phytomass for this semi-arid area, with an increase in roots in relation to aboveground phytomass production with rangeland degradation. The mean monthly root/shoot ratios for rangelands in good, moderate and poor conditions were 1.16, 1.11 and 1.37, respectively. Rangeland degradation significantly lowered above- and belowground phytomass production as well as the water-use efficiency. The mean WUE (root production included) were 4.79, 3.54 and 2.47 kg ha −1 mm −1 for rangelands in good, moderate and poor conditions, respectively. These water-use efficiency observations are among the few also including root production in its calculation. As a proportion of annual phytomass, litter fall of 7.17, 4.64 and 3.41% was obtained for rangelands in good, moderate and poor conditions, respectively. Increasing rangeland degradation increased the replacement of total root system by about 10 months and decomposition time of litter by 6 months. The importance of a well-established root system for sustainable production in the semi-arid rangelands cannot be overemphasized.