Spatial-temporal characteristics of epidemic spread in-out flow——Using SARS epidemic in Beijing as a case study

For better detecting the spatial-temporal change mode of individual susceptible-infected-symptomatic-treated-recovered epidemic progress and the characteristics of information/material flow in the epidemic spread network between regions,the epidemic spread mechanism of virus input and output was explored based on individuals and spatial regions.Three typical spatial information parameters including working unit/address,onset location and reporting unit were selected and SARS epidemic spread in-out flow in Beijing was defined based on the SARS epidemiological investigation data in China from 2002 to 2003 while its epidemiological characteristics were discussed.Furthermore,by the methods of spatial-temporal statistical analysis and network characteristic analysis,spatial-temporal high-risk hotspots and network structure characteristics of Beijing outer in-out flow were explored,and spatial autocorrelation/heterogeneity,spatial-temporal evolutive rules and structure characteristics of the spread network of Beijing inner in-out flow were comprehensively analyzed.The results show that(1)The outer input flow of SARS epidemic in Beijing concentrated on Shanxi and Guangdong provinces,but the outer output flow was disperse and mainly includes several north provinces such as Guangdong and Shandong.And the control measurement should focus on the early and interim progress of SARS breakout.(2)The inner output cases had significant positive autocorrelative characteristics in the whole studied region,and the high-risk population was young and middle-aged people with ages from 20 to 60 and occupations of medicine and civilian labourer.(3)The downtown districts were main high-risk hotspots of SARS epidemic in Beijing,the northwest suburban districts/counties were secondary high-risk hotspots,and northeast suburban areas were relatively safe.(4)The district/county nodes in inner spread network showed small-world characteristics and information/material flow had notable heterogeneity.The suburban Tongzhou and Changping districts were the underlying high-risk regions,and several suburban districts such as Shunyi and Huairou were the relatively low-risk safe regions as they carried out minority information/material flow.The exploration and analysis based on epidemic spread in-out flow help better detect and discover the potential spatial-temporal evolutive rules and characteristics of SARS epidemic,and provide a more effective theoretical basis for emergency/control measurements and decision-making.     

Influences of retrogressive erosion of reservoir on sedimentation of its downstream river channel——A case study on Sanmenxia Reservoir and the Lower Yellow River

Retrogressive erosion, a widespread phenomenon of sediment transport in reservoirs, often impacts on both the reservoir capacity and the sedimentation in the downstream river channel. Based on field data from the Sanmenxia Reservoir and the Lower Yellow River over the past decades, three courses of ret-rogressive erosion with distinctive features were analyzed. The results indicate that retrogressive erosion, especially caused by rapid reduction in the water level till the reservoir is empty, often results in the serious siltation of the lower Yellow River and threatens the safety of the flood control in the Lower Yellow River. Unreasonable operation of the reservoir and incoming hyperconcentrated floods accom-panied by retrogressive erosion also aggravate the siltation of the main channel of the river. However, a reasonable operation mode of the reservoir so named"storing the clear (low sediment concentration) water in the non–flood season, and sluicing the muddy(high sediment concentration) water in the flood season" was found, which might mitigate the deposition in both the reservoir and the Lower Yellow River. This operation mode provides important experience for the design and operation of large reser-voirs in other large rivers carrying huge amounts of sediment.     

Influence of deposition of fine plant debris in river floodplain shrubs on flood flow conditions – The Warta River case study

This paper presents problems caused by organic material transported by flowing water. This material is usually referred to as plant debris or organic debris. Its composition depends on the characteristic of the watercourse. For lowland rivers, the share of the so-called small organic matter in plant debris is considerable. This includes both various parts of water plants and floodplain vegetation (leaves, stems, blades of grass, twigs, etc.). During floods, larger woody debris poses a significant risk to bridges or other water engineering structures. It may cause river jams and may lead to damming of the flowing water. This, in turn, affects flood safety and increases flood risk in river valleys, both directly and indirectly. The importance of fine plant debris for the phenomenon being studied comes down to the hydrodynamic aspect (plant elements carried by water end up on trees and shrubs, increase hydraulic flow resistance and contribute to the nature of flow through vegetated areas changed from micro-to macro-structural). The key part of the research problem under analysis was to determine qualitative and quantitative debris parameters and to establish the relationship between the type of debris and the type of land use of river valleys (crop fields, meadows and forested river sections). Another problem was to identify parameters of plant debris for various flow conditions (e.g. for low, medium and flood flows). The research also included an analysis of the materials deposited on the structure of shrubs under flood flow conditions during the 2010 flood on the Warta River.     

Simulation analysis on the regulation of overflow ecological water consumption in arid areas——A case study in the Canmrik ecological area of the mainstream zone of the Tarim River

After analyzing the regulation of overflow ecological water consumption in the Canmrik ecological area of mainstream zone of the Tarim River, in this paper a model of ecological bifurcation is developed, the dynamic overflow process of ecological bifurcation is simulated, and the quantitative relationships between the volume of ecological water consumption and the ecological conservation extent and overflow time are analyzed using GIS, advance of freshet and RS means. The results reveal that the effects of discharge and time of ecological bifurcation on the efficiency of ecological water consump-tion are significant, there is a geometrical exponential relationship between the efficiency of ecological bifurcation and the water supply with different discharges and different times under the same eco-logical water consumption, hypsography plays an important role in ecological water consumption, the regulation of ecological water consumption cannot be equated with the ordinary farming irrigation system, a serious water waste will result and the prospective ecological benefits will not be able to be achieved if an ordinary ecological bifurcation is implemented. The efficiency of ecological water con-sumption can be increased by 30% by selecting the bifurcation schemes in an optimized way, which is of the utmost importance for arid areas with shortage of water resources.     

Experimental study on the influence of river flow confluences on the open channel stage–discharge relationship

ABSTRACT

Accurate assessment of stage–discharge relationships in open channel flows is important to the design and management of hydraulic structures and engineering. Flow junctions commonly occur at the confluence of natural rivers or streams. The effect of flow junctions on the stage–discharge relationship at mountain river confluences was found by measuring velocity fields and water levels in experimental models. The results show that the backwater and accumulation–separation at flow junctions affect the flow structures and patterns in the channel; also, flow confluences may induce complex flow characteristics of backwater and flow separation at river junctions, indicating potential submerged flooding disasters within the confluence zone. The impacts of flow junctions on the stage–discharge relationship are investigated for two physical confluence models built from river confluence prototype systems in southwest China. The results show that the presence of tributary river inflows tends to increase the water level of the main river. This is important for flood control, flood-risk evaluation and engineering (e.g. hydropower station construction) in mountain rivers. Finally, a comparative quantitative analysis based on flow motion equations is conducted to evaluate the stage–discharge relationship in both uniform and regular confluence systems. The results indicate that more accurate prediction can be made when taking into account the flow non-uniformity induced by flow separation, backwater and distorted bed in the junction region.     

Hydrodynamic characteristics of Wujiangdu Reservoir during the dry season—a case study of a canyon reservoir

With the development of hydropower in the karst area of Southwest China, a series of cascade canyon reservoirs have been formed through the construction of dams. Given that hydrodynamic conditions in canyon reservoirs play a pivotal role in controlling the spatiotemporal distribution of physical and chemical properties of the stored water, hydrodynamic characteristics are of great importance in understanding biogeochemical cycles in those reservoirs. To further this understanding, a field campaign was conducted in the Wujiangdu Reservoir of Guizhou Province. It was found that from the reservoir inlet to the front of the dam, velocity(v) was negativelycorrelated and had a logarithmic relationship with distance along the ship track(s) under dry-season flow conditions[v =-0.104 ln(s) + 0.4756]. Analysis showed that dryseason flow velocity had no significant correlation with water temperature, p H, or dissolved oxygen(DO). However, when velocity decreased to 0.061 m/s, water depth increased abruptly. In addition, DO displayed a sudden drop and the trend in p H changed from increasing to decreasing, while water temperature showed an opposite trend, indicating the existence of a transition zone from the river to the reservoir.     

Three-dimensional flow patterns at the river–aquifer interface — a case study at the Danube

The three-dimensional groundwater flow patterns in a gravel bar at the Danube east of Vienna were investigated and are discussed in this paper. The observed groundwater level gradients are highly dynamic and respond very quickly to changes in the river water levels. A variably saturated groundwater model was calibrated to the data to describe the complex dynamics of flow in the gravel bar. The model results suggest that short-term (6–48 h) fluctuations of river water levels cause variations in the exchange flow rates from − 35 l/s to 82 l/s. The highest rates occur during brief infiltration after rapidly rising river water levels. Simulations of different scenarios indicate that riverbank clogging will decrease the exchange fluxes by up to 80%, while clogging of both riverbank and riverbed essentially stops the flow exchange. The groundwater model is also used to simulate the transport of a conservative tracer. The variation of river water levels over time is shown to increase the extent of the active river–aquifer mixing zone in the gravel bar. These dynamic factors significantly enhance the dilution of conservative tracer concentrations in this zone.     

Impact of climate and land-use changes on hydrological processes and sediment yield—a case study of the Be River catchment,Vietnam

Abstract

The impact of climate and land-use changes on hydrological processes and sediment yield is investigated in the Be River catchment, Vietnam, using the Soil and Water Assessment Tool (SWAT) hydrological model. The sensitivity analysis, model calibration and validation indicated that the SWAT model could reasonably simulate the hydrology and sediment yield in the catchment. From this, the responses of the hydrology and sediment to climate change and land-use changes were considered. The results indicate that deforestation had increased the annual flow (by 1.2%) and sediment load (by 11.3%), and that climate change had also significantly increased the annual streamflow (by 26.3%) and sediment load (by 31.7%). Under the impact of coupled climate and land-use changes, the annual streamflow and sediment load increased by 28.0% and 46.4%, respectively. In general, during the 1978–2000 period, climate change influenced the hydrological processes in the Be River catchment more strongly than the land-use change.

Editor Z.W. Kundzewicz; Associate editor Q. Zhang

Citation Khoi, D.N. and Suetsugi, T., 2014. Impact of climate and land-use changes on hydrological processes and sediment yield—a case study of the Be River catchment, Vietnam. Hydrological Sciences Journal, 59 (5), 1095–1108.     

A preliminary study on the heat storage fluxes of a tropical seasonal rain forest in Xishuangbanna

In order to discuss the values and daily variation characteristics of heat storage fluxes in a tropical seasonal rain forest in Xishuangbanna, the sensible and latent heat storage flux within air column, canopy heat storage flux, energy storage by photosynthesis and ground heat storage above the soil heat flux plate, as well as the ratios of these heat storage fluxes to the net radiation in the cool-dry, hot-dry and rainy season were compared and analyzed based on the observation data of carbon fluxes, meteorological factors and biomass within this tropical seasonal rain forest from January 2003 to December 2004. The findings showed that heat storage terms ranged significantly in the daytime and weakly in the nighttime, and the absolute values of sensible and latent heat storage fluxes were obviously greater than other heat storage terms in all seasons. In addition, the absolute values of total heat storage fluxes reached the peak in the hot-dry season, then were higher in the rainy season, and reached the minimum in the cool-dry season. The ratios of heat storage fluxes to net radiation generally decreased with time in the daytime, moreover, the sensible and latent heat storage dominated a considerable fraction of net radiation, while other heat storage contents occupied a smaller fraction of the net radiation and the peak value was not above 3.5%. In the daytime, the ratios of the total heat storage to net radiation were greater and differences in these ratios were distinct among seasons before 12:00, and then they became lower and differences were small among seasons after 12:00. The energy closure was improved when the storage terms were considered in the energy balance, which indicated that heat storage terms should not been neglected. The energy closure of tropical seasonal rain forest was not very well due to effects of many factors. The results would help us to further understand energy transfer and mass exchange between tropical forest and atmosphere. Moreover, they would supply a research basis for studying energy closure at other places.     

A case study of the evolution of a Kelvin–Helmholtz wave and turbulence in noctilucent clouds

Bright and extensive noctilucent clouds (NLC) were observed in Århus (Denmark) on 3/4 July of 2008 with an automatic digital camera taking images every minute. This event was unique in the sense that bright NLC were seen at high elevation angles (more than 30°) that allowed observing the evolution of a Kelvin–Helmholtz (KH) wave, resulted in well-developed turbulence. In particular, coherent vortex structures of a horseshoe-shaped form were observed for the first time in noctilucent clouds. The turbulent diffusion coefficient and turbulent energy dissipation rate around the mesopause are estimated in the range 162–667 m²/s and 300–1235 mW/kg, respectively, representing a case of strong neutral air turbulence in noctilucent clouds. Turbulent structures were observed to be in the vicinity of breaking small-scale gravity waves that seems to be responsible for a high level of turbulence.At the same time, it has been demonstrated that it is of importance to take into account non-turbulent process such as the gravity wave motion that is always present in NLC layers. Unless non-turbulent process is taken into account, this certainly leads to overestimating of the value of the turbulent diffusion coefficient. More accurate characteristics of turbulence in NLC can be obtained by analyzing a sequence of high-resolution images with a high frame-rate high-resolution digital camera.     

Changes in the plain river system and its hydrological characteristics under urbanization – case study of Suzhou City,China

ABSTRACT

Rapid urbanization in China has severely disturbed the underlying surface and river systems. The stream structure parameters of Suzhou City were analysed to study the evolution and spatial differentiation of a water system undergoing urbanization. The influencing pattern of different urbanization processes on river system structure and hydrological processes was detected by statistical methods and simulation analysis. The results show that urban sprawl is influenced by both the natural environment and the social economy. At different stages of urbanization, the spatial urban expansion and the natural river characteristics influence the evolution of the river network: during rapid urbanization, the decline in surface water ratio and river density is more intense. The decrease of surface water ratio and river density in rapidly urbanized areas was greatest, followed by that in area urbanized in the 1980s, with few changes in the old town. Under high urbanization, river system indicators tend to stabilize. The rivers’ hydrological features were affected by urbanization, with water yield in the study area increasing from 0.81 to 0.95 m³/m² (1991–2015). The same rainfall intensity results in higher flood levels and greater risk of flooding under rapid urbanization.     

Spatial variations of terrain and their impacts on landscape patterns in the transition zone from mountains to plains—A case study of Qihe River Basin in the Taihang Mountains

Terrain plays a key role in landscape pattern formation, particularly in the transition zones from mountains to plains. Exploring the relationships between terrain characteristics and landscape types in terrain-complex areas can help reveal the mechanisms underlying the relationships. In this study, Qihe River Basin, situated in the transition zone from the Taihang Mountains to the North-China Plain, was selected as a case study area. First, the spatial variations in the relief amplitudes (i.e., high-amplitude terrain undulations) were analyzed. Second, the effects of relief amplitudes on the landscape patterns were indepth investigated from the perspectives of both landscape types and landscape indices. Finally, a logistic regression model was employed to examine the relationships between the landscape patterns and the influencing factors (natural and human) at different relief amplitudes. The results show that with increasing relief amplitude, anthropogenic landscapes gradually give in to natural landscapes. Specifically, human factors normally dominate the gentle areas (e.g., flat areas) in influencing the distribution of landscape types, and natural factors normally dominate the highly-undulating areas (e.g., moderate relief areas). As for the intermediately undulating areas (i.e., medium relief amplitudes), a combined influence of natural and human factors result in the highest varieties of landscape types. The results also show that in micro-relief areas and small relief areas where natural factors and human factors are more or less equally active, landscape types are affected by a combination of natural and human factors. The combination leads to a high fragmentation and a high diversity of landscape patterns. It seems that appropriate human interferences in these areas can be conducive to enhancing landscape diversity and that inappropriate human interferences can aggravate the problems of landscape fragmentation.     

Monitoring heat losses using Landsat ETM+ thermal infrared data — a case study at Kuju fumarolic area in Japan

To monitor heat losses using Landsat 7 thermal infrared data from 2002 to 2010 within the active fumarolic region of Kuju volcano in Japan, we used the Stefan-Boltzmann equation for radiative heat flux (RHF) estimation. Heat discharge rate (HDR) was calculated by using the relationship coefficient of RHF and HDR, obtained from two previous studies. The highest total RHF was found to be about 57.7 MW in 2002 and the lowest was about 21.1 MW in 2010. We found the highest HDR, of about 384.5 MW, in 2002 and the lowest, of about 140.8 MW, in 2010. The RHF anomalous areas were showing a declining trend during our study period. The relationship between the land surface temperature (LST) above ambient and RHF was, as expected, in a strong correlation for each result during our study period. Overall, our study was able to delineate the declining trend of heat losses that supports a previous study of similar declining trend of HDR using steam maximum diameter method from the active fumarolic region of Kuju volcano.     

Where do periodic variations in the discharge of a well become negligible?

A rule of thumb is presented to determine where variations in the discharge of a pumping well have a significant influence on the flow in an aquifer. The rule of thumb relates the period of the variation of the discharge to the distance from the well beyond which the transient effect on the flow in the aquifer is insignificant. For example, when an irrigation well pumps intermittently during the growing season, the rule may be applied to determine the distance from the well beyond which flow in the aquifer can be simulated with an average discharge during the growing season; the distance from the well beyond which flow can be simulated with a steady, yearly averaged discharge can also be computed.     

A case study of the mesoscale dynamics in the North-Western Mediterranean Sea: a combined data–model approach

The Northern current is the main circulation feature of the North-Western Mediterranean Sea. While the large-scale to mesoscale variability of the northern current (NC) is well known and widely documented for the Ligurian region, off Nice or along the Gulf of Lions shelf, few is known about the current instabilities and its associated mesoscale dynamics in the intermediate area, off Toulon. Here, we took advantage of an oceanographic cruise of opportunity, the start of a HF radar monitoring programme in the Toulon area and the availability of regular satellite sea surface temperature and chlorophyll a data, to evaluate the realism of a NEMO-based regional high-resolution model and the added value brought by HF radar. The combined analysis of a 1/64° configuration, named GLAZUR64, and of all data sets revealed the occurrence of an anticyclonic coastal trapped eddy, generated inside a NC meander and passing the Toulon area during the field campaign. We show that this anticyclonic eddy is advected downstream along the French Riviera up to the study region and disturbs the Northern current flow. This study aims to show the importance of combining observations and modelling when dealing with mesoscale processes, as well as the importance of high-resolution modelling.     

Impact of the greenhouse effect on sewerage systems—Lund case study

Abstract

The possible impacts of modifications in rainfall patterns due to the greenhouse effect on the function of a sewerage system are studied based on a case study of the city of Lund, Sweden. The Storm Water Management Model is used to simulate changes in the runoff pattern. The paper lists the possible effects of increases in rainfall intensity on the urban water cycle, quantifies changes in the runoff pattern, and discusses the significance of detected changes in terms of economic and environmental consequences and the possibilities to undertake preventative measures. For the purpose of the present study, 10%, 20% and 30% levels of rainfall increase were assumed. In spite of considerable uncertainty regarding the potential future rate of hydrological changes, the examples given of possible impacts of the greenhouse effect on the function of the sewerage system bear witness to the great vulnerability of sewerage systems to the results of climate changes.     

Producing time series of river water height by means of satellite radar altimetry—a comparative study

Abstract

Satellite radar altimetry is complementary to in situ limnimetric surveys as a means of estimating the water height of large rivers, lakes and flood plains. Production of water height time series by satellite radar altimetry technology requires first the selection of radar ground target locations corresponding to water body surfaces under study, i.e. the definition of “virtual limnimetric stations”. We propose to investigate qualitative and quantitative differences between three representative virtual station creation methodologies: (a) a fully manual method, (b) a semi-automatic method based on a land cover characterization that allows the water body surface under study to be located; and (c) an original fully automatic procedure that exploits a digital elevation model and an estimation of the river width. The results yielded by these three methods are comparable: maximum absolute magnitudes of water height differences being 0.46, 0.26 and 0.15 m for, respectively, 95, 90 and 80% of the water height values obtained. Moreover, more than 67% and 92% of time series jointly produced by the methods present root mean square differences lower than 20 and 50 cm, respectively. The results show that the fully automatic method developed herein provides as reliable results as the fully manual one. This opens the way to use of satellite radar altimetry for the generation of water height time series on a large scale, and considerably extends the applicability of satellite radar altimetry in hydrology.

Citation Roux, E., Santos da Silva, J., Vieira Getirana, A. C., Bonnet, M.-P., Calmant, S., Martinez, J.-M. & Seyler, F. (2010) Producing time series of river water height by means of satellite radar altimetry—comparative study. Hydrol. Sci. J. 55(1), 104–120.     

Long-range dependence in the time series of Taiţa River discharges

ABSTRACT

The aim of this article is to offer an insight into the hydrology of southeast Romanian catchments, which have not been studied systematically. The complex behaviour of the Tai?a, one of the most important rivers situated in the northern part of Dobrogea, is demonstrated. Long-range dependence (LRD) in the time series of its streamflow, including the presence of trends, is supported by an estimated Hurst exponent of approximately 0.8, as well as statistical tests.

Editor D. Koutsoyiannis; GUEST editor S. Weijs     

Trend and change-point analyses of streamflow and sediment discharge in the Yellow River during 1950–2005

Abstract

The objectives of this work are: (a) to statistically test and quantify the decreasing trends of streamflow and sediment discharge of the Yellow River in China during 1950–2005, (b) to identify change points or transition years of the decreasing trends, and (c) to diagnose whether the decreasing trends were caused by precipitation changes or human intervention, or both. The results show that significant decreasing trends in annual streamflow and sediment discharge have existed since the late 1950s at three stations located in the upper, middle, and lower reaches of the Yellow River (P?=?0.01). Change-point analyses further revealed that transition years existed and that rapid decline in streamflow and sediment discharge began in 1985 in most parts of the basin (P?=?0.05). Adoption of conservation measures in the 1980s and 1990s corroborates the identified transition years. Double-mass curves of precipitation vs streamflow (sediment) for the periods before and after the transition years show remarkable decreases in proportionality of streamflow (sediment) generation. All percentiles of streamflow and sediment discharge after the transition years showed rapid reduction. In the absence of significantly decreasing precipitation trends, it is concluded that the decreasing trends were very likely caused by human intervention. Relative to the period before the transition, human intervention during 1985–2005 reduced cumulative streamflow by 13.5, 14.3 and 24.6% and cumulative sediment discharge by 29.0, 24.8 and 26.5%, at Toudaoguai, Huayuankou and Lijin, respectively, showing the quantitative conservation effect in the basin.

Citation Gao, P., Zhang, X.-C., Mu, X.-M., Wang, F., Li, R. & Zhang, X. (2010) Trend and change-point analyses of streamflow and sediment discharge in the Yellow River during 1950–2005. Hydrol. Sci. J. 55(2), 275–285.