1,721,097 research outputs found
Assessment of the effects of climate variability and land use changes on the hydrology of the Meuse River Basin
Full text linkUhlenbrook, S. [Promotor]Laat, P. de [Copromotor
Catchment modelling: towards an improved representation of the hydrological processes in real-world model applications
No full textCatchment hydrology: hydrological processes and distributed modelling
No full textSimposio tenuto in occasione della General Assembly della European Geosciences Unio
Space-time variation of hydrological processes and water resources in Rwanda: Focus on the Migina catchment
No full textThis book presents the hydrological research carried out in the Migina catchment (260 km2), Southern Rwanda. The main objective of the research is to explore the hydrological trends and climate linkages for catchments in Rwanda (26,338 km2), and to contribute to the understanding of dominant hydrological process interactions. Different hydro-meteorological instrumentations have been installed in the Migina catchment during April 2009 to July 2009 and measurements have been carried out and are still ongoing. The trend analysis is based on Mann-Kendall (MK) test and Pettitt test on times series data varying from 30 to 56 years before 2000. The hydrometric data and modern tracer methods are used for hydrograph separation and show that subsurface runoff is dominating the total discharge even during rainy seasons of May 2010 and 2011 at Cyihene-Kansi and Migina sub-catchments, respectively. Further, a semi-distributed conceptual hydrological model HEC-HMS is applied for assessing the spatio-temporal variation of water resources in the Migina catchment. The model results are compared with tracer based hydrograph separation results in terms of the runoff components. The model performed reasonably well in simulating the total flow volume, peak flow and timing as well as the portion of direct runoff and baseflow.Water ManagementCivil Engineering and Geoscience
Transport of multiple Escherichia coli strains in saturated porous media
No full textThe deviation of bacteria transport and deposition patterns on grains in porous media from theory has resulted in the inability to accurately predict transport distances in aquifers, with consequences of polluting drinking water sources (springs, boreholes and wells). Due to the importance of Escherichia coli (E. coli) as an indicator of faecal contamination of drinking water supplies, this thesis research focused on their transport in saturated porous media. The objectives were to (i) study inter-strain and intra-strain attachment variability among multiple E. coli strains, (ii) characterize the distribution of sticking efficiencies within cell populations (iii) develop a methodology to measure minimum values of sticking efficiencies, and (iv) to assess the contribution of various cell properties on bacterial attachment to quartz grains. Most of this research was carried out under laboratory conditions (e.g. column and batch experiments), but a part of this work focused on the transport characteristics of E. coli strains isolated at the termination point of groundwater flow lines (springs) in Kampala, Uganda. The underlying hypothesis was that transport by a group of E. coli strains could possibly be characterized by a similar set of transport parameters. Transport of E. coli strains isolated from different sources of the environment was studied using saturated quartz columns. Short (7 cm) and long (1.5 - 25 m) columns were used to investigate inter-strain attachment variations among E. coli strains, distributions in attachment efficiency within E. coli strains and to develop a methodology to measure the minimum sticking efficiency. Furthermore, long column experiments were applied in order to be able to measure low sticking efficiency values. Prior to the experiments E. coli strains were cultured and their phenotypic characteristics and selected genes encoding structures at the outer membrane were measured to investigate their effects on transport/attachment. The results indicated that none of the studied cell characteristics significantly influenced E. coli attachment on sedimentary quartz grains; however, cell motility and antigen-43 expression promoted attachment to quartz grains over relatively short transport distances. For spring E. coli isolates from Kampala, a substantial percentage belonged to the same serotype (E. coli O21:H7). Therefore, we concluded that strains possessing this particular serotype may possess certain characteristics that promote their selective transport through the aquifers in the Kampala area in Uganda and might have determined an overall transport homogeneity observed for this particular group of E. coli isolates. With the exception of spring E. coli isolates which showed overall inter-strain transport homogeneity, results indicated that intra-strain and inter-strain attachment heterogeneities existed within and among the various E. coli strains, respectively. Environmentally relevant low values of sticking efficiencies were measured over long transport distances and thus demonstrated the importance of the use of long columns for this type of research. The measured low values of sticking efficiency indicated that, for bacterial populations leaked into groundwater environments, sub-populations may possess non-attaching characteristics and therefore increase their chances of being transported over considerable distances, that might be underestimated using common drinking water protection guidelines. Intra-strain attachment variability resulted in a power-law distribution between fraction of cells and their sticking efficiencies. Minimum sticking efficiency was extrapolated from the power-law distribution. The minimum sticking efficiency is defined as the sticking efficiency belonging to a bacteria fraction of 0.001% of initial bacteria mass flowing into a column, after removal of 99.999% (5 log reduction) of the original bacteria mass has taken place. Values extrapolated were lower than those measured from experiments; the low values make the minimum sticking efficiency a valuable tool in delineating well-head protection areas in real-world cases. Future research should focus on cell surface structures known to be involved in initial attachment to host tissues and/or abiotic surfaces. In addition, we advocate to carry out field bacteria transport experiments instead of laboratory experiments, since interpreting the results of the latter is limited by transport dependent scale issues.Water ManagementCivil Engineering and Geoscience
Understanding hydrological variability for improved water management in the Semi-Arid Karkheh basin, Iran
No full textThis study provides a hydrology based assessment of (surface) water resources and its continuum of variability and change at different spatio-temporal scales in the semi-arid Karkheh Basin, Iran, where water is scarce, competition among users is high and massive water resources development is under way. The study reveals that the ongoing allocation planning is not sustainable and essentially requires reformulation, with consideration of spatio-temporal variability and observed trends in the streamflows regarding flood intensification and decline in low flows. The development of innovative methods for quantification of the hydrological fluxes (i.e., regionalization of model parameters based on similarity of the flow duration curve and the use of areal precipitation input in the hydrological modeling) helped better understanding and modeling the basin hydrology. The investigation of scenarios for upgrading rain-fed areas to irrigated agriculture, using SWAT, recommends the promotion of in-situ soil and water conservation techniques. Conversion of rain-fed areas to irrigation causes significant reduction in the downstream flows, and requires additional considerations such as less development in the upper catchments, practicing supplementary irrigation and developing water storage. The knowledge generated is instructive for hydrological assessment and its use in water resources planning and management in the river basin context.Civil Engineering and Geoscience
Water Tower of the Yellow River in a Changing Climate: Toward an integrated assessment
No full textClimate change due to increasing greenhouse gas emissions is likely to alter the hydrological cycle resulting in large impacts on water resources worldwide. Mountain regions are important sources of freshwater for the entire globe, but their role in global water resources could be significantly altered by climate change. Mountains are expected to be more sensitive and vulnerable to global climate change than other land surface at the same latitude owing to the highly heterogeneous physiographic and climatic settings. Furthermore, there is also evidence from observational and modelling studies for an elevation-dependent warming within some mountain regions. With the increasing certainty of global climate change, it is important to understand how climate will change in the 21st century and how these changes will impact water resources in these mountain regions. Our understanding of climate change and the associated impacts on water availability in mountains is restricted due to inadequacies in observations and models. This is also the case in the Yellow River source region (YRSR). The YRSR is often referred to as the water tower of the Yellow River as it contributes about 35% of the total annual runoff of the entire Yellow River. Located in the northeast Tibetan Plateau, a “climate change hot-spot” and one of the most sensitive areas to greenhouse gas (GHG)-induced global warming, the potential impacts of climate change on water resources in this region could be significant with unknown consequences for water availability in the entire Yellow River basin. The YRSR is relatively undisturbed by anthropogenic influences such as abstractions and damming, which enables the characterization of largely natural, climate-driven changes. A growing number of studies suggest that the YRSR is experiencing warming and streamflow reduction in recent decades, which has drawn increasing attention about the future climate changes and their impacts on water availability. While most previous studies focused on historical changes in the mean values of hydroclimatic conditions, future climate change impacts were less explored. Additionally, compared to assessing the impact of a change in average hydroclimatic condition, changes in extremes were solely missing in this region in spite of high relevance of such events on our society. This study attempts to fill these research gaps by investigating the spatial and temporal variability of both recent and future climate change impacts with specific focus on extremes. An integrated approach is applied consisting of (i) statistical analysis of historic data, (ii) downscaling of large-scale climate projections and (iii) hydrological modelling. This study contributes towards an improved understanding of spatial and temporal variability of climate change impacts in the YRSR through four major topics. The first topic focuses on the assessment of recent climate change impacts in the YRSR. Historical trends in a number of temperature, rainfall and streamflow indices representing both mean values and extreme events are analyzed over the last 50 years. The linkages between hydrological and climatic variables are also explored to better understand the nature of recent observed changes in hydrological variables. Significant warming trends have been observed for the whole study region. This warming is mainly attributed to the increase in the minimum temperature as a result of the increase in magnitude and decrease in frequency of low temperature events. In contrast to the temperature indices, the trends in rainfall indices are less distinct. However, on a basin scale increasing trends are observed in winter and spring rainfall. Conversely, the frequency and contribution of moderately heavy rainfall events to total rainfall show a significant decreasing trend in summer. In general, the YRSR is characterized by an overall tendency towards decreasing water availability, which is shown by decreasing trends in a number of indices in the observed discharge at the outlet of basin over the period 1959–2008. The hydrological variables studied are closely related to precipitation in the wet season (June, July, August and September), indicating that the widespread decrease in wet season precipitation is expected to be associated with significant decrease in streamflow. To conclude, this study shows that over the past decades the YRSR has become warmer and experienced some seasonally varying changes in rainfall, which also supports an emerging global picture of warming and the prevailing positive trends in winter rainfall extremes over the mid-latitudinal land areas of the Northern Hemisphere. The decreasing precipitation, particularly in the wet season, along with increasing temperature can be associated with pronounced decrease in water resources, posing a significant challenge to downstream water uses. In the second topic, three statistical downscaling methods are compared with regard to their ability to downscale summer (June–September) daily precipitation to a network of 14 stations over the Yellow River source region from the NCEP/NCAR reanalysis data with the aim of constructing high-resolution regional precipitation scenarios for impact studies. The methods used are the Statistical Downscaling Model (SDSM), the Generalized LInear Model for daily CLIMate (GLIMCLIM) and the non-homogeneous Hidden Markov Model (NHMM). The methods are compared using several criteria, such as spatial dependence, wet and dry spell length distributions and inter-annual variability. In comparison with other two models, NHMM shows better performance in reproducing the spatial correlation structure, inter-annual variability and magnitude of the observed precipitation. But its performance is less satisfactory in reproducing observed wet and dry spell length distributions at some stations. SDSM and GLIMCLIM showed better performance in reproducing the temporal dependence than NHMM. These models are also applied to derive future scenarios for six precipitation indices for the period 2046-2065 using the predictors from two global climate models (GCMs; CGCM3 and ECHAM5) under the IPCC SRES A2, A1B and B1scenarios. There is a strong consensus among two GCMs, three downscaling methods and three emission scenarios in the precipitation change signal. Under the future climate scenarios considered, all parts of the study region would experience increases in rainfall totals and extremes that are statistically significant at most stations. The magnitude of the projected changes is more intense for the SDSM than for other two models, which indicates that climate projection based on results from only one downscaling method should be interpreted with caution. The increase in the magnitude of rainfall totals and extremes is also accompanied by an increase in their inter-annual variability. In the third topic, we investigate possible changes in mean and extreme temperature indices and their elevation dependency over the YRSR for the two future periods 2046–2065 and 2081–2100 using statistically downscaled outputs from two CGMs under three IPCC SRES emission scenarios (A2, A1B and B1). The projections show that by the middle and end of the 21st century all parts of the study region may experience increases in both mean and extreme temperature in all seasons, along with an increase in the frequency of hot days and warm nights and decrease in frost days. By the end of the 21st century, inter-annual variability increases in the frequency of hot days and warm nights in all seasons. The frost days show decreasing inter-annual variability in spring and increasing one in summer. Six out of eight temperature indices in autumn show significant increasing changes with elevation. The fourth topic presents a modelling study on the spatial and temporal variability of the future climate-induced hydrologic changes in the YRSR. A fully distributed, physically based hydrologic model (WaSiM) was employed to simulate baseline (1961-1990) and future (2046–2065 and 2081–2100) hydrologic regimes based on climate change scenarios. The climate chance scenarios are statistically downscaled from two GCM outputs under three emissions scenarios (B1, A1B and A2). All climate change projections used here show yearround increases in both precipitation and temperature, which result in significant increases in streamflow and evaporation on both annual and seasonal basis. High flow is expected to increase considerably in most projections, whereas low flow is expected to increase slightly. Snow storage is projected to considerably decrease while the peak flow is likely to occur later. We also observe a significant increase in soil moisture on annual basis owing to increased precipitation. Overall, the projected increases in all the hydro-climatic variables considered are greater for the mid of the century than for the end of the century. The magnitude of the projected changes varies across the subbasins, and is different under different emission scenarios and GCMs, indicating the uncertainty involved in the impact analysis. Inconsistency of observed streamflow trends with future projections indicates that the recently observed streamflow trends cannot be used as an illustration of plausible expected future changes in the YRSR. Such inconsistency calls for an urgent need for research aiming to reconcile the historical changes with future projections. This study has covered a wide range of topics and a number of relevant issues of hydrology, climate change and downscaling in mountain areas. The applied multidisciplinary approach has clearly added value and provided new insights (e.g. multisite downscaling in a mountainous catchment, climate-induced changes in extremes) and opened many new avenues for scientific research in the future to be explored including investigating the potential feedbacks between land cover change and climate change and reconciling the observed trends with future projections. In general, the knowledge generated in this study can be used as the basis of local scale adaptive water resources management in a changing climate.Water ManagementCivil Engineering and Geoscience
Fate and Transport of Nutrients in Groundwater and Surface Water in an Urban Slum Catchment Kampala, Uganda
No full textThis study investigates the generation, transport and fate of sanitation-related nutrients in groundwater and surface water in an urban slum area in sub-Saharan Africa. In excess, nutrients can cause eutrophication of downstream water bodies. The study argues that nitrogen-containing rains and domestic wastewater from slum areas were important sources of nutrients in urban catchments. Contrary to surface water, nutrients were greatly attenuated in groundwater by the pit latrine-alluvial aquifer system implying that interventions to manage nutrients in slum areas should focus on surface water. This research is of broad interest as urbanisation in developing countries is an ongoing trend that is accompanied by lack proper sanitation systems.Water managementCivil Engineering and Geoscience
Assessing the impact of climate change upon hydrology and agriculture in the Indrawati Basin, Nepal.
No full textAgriculture is sensitive to climate change, especially to temperature and precipitation changes. The purpose of this study was to evaluate the climate change impacts upon rain-fed crops production in the Indrawati river basin, Nepal. The Soil and Water Assessment Tool SWAT model was used to model hydrology and cropping systems in the catchment, and to predict the influence of different climate change scenarios therein. Daily weather data collected from about 13 weather stations during 4 decades were used to constrain the SWAT model, and data from two hydrometric stations used to calibrate/validate it. Then management practices (crop calendar) were applied to specific Hydrological Response Units (HRUs) for the main crops of the region, rice, corn and wheat. Manual calibration of crop production was also carried, against values of crop yield in the area from literature. The calibrated and validated model was further applied to assess the impact of three future climate change scenarios (RCPs) upon the crop productivity in the region. Three climate models (GCMs) were adopted, each with three RCPs (2.5, 4.5, 8.5). Hence, impacts of climate change were assessed considering three time windows, namely a baseline period (1995-2004), the middle of century (2045-2054) and the end of century (2085-2094). For each GCM and RCP future hydrology and yield was compared to baseline scenario. The results displayed slightly modified hydrological cycle, and somewhat small variation in crop production, variable with models and RCPs, and for crop type, the largest being for wheat
Impact of prospective climate change on water resources and crop yields in the Indrawati basin, Nepal
No full textThe study aimed at developing a tool to investigate the effect of prospective climate change (until 2100) on hydrology and productivity of rain-fed crops (wheat Triticum L., maize Zea Mais L., and rice Oryza L.) in the Indrawati river basin, Nepal, Himalaya. Climate scenarios from 3 climate models (GCMs), namely CCSM4, EC-Earth and ECHAM6, each one under 3 different representative concentration pathways (RCPs) were fed to Soil and Water Assessment Tool (SWAT) and hydrological fluxes and crop yields were estimated for two time windows, i.e. half century (2045-2054) and end of century (2085-2094) against control run decade (1995-2004). The results foresee considerable potential changes of hydrological fluxes (from -26% to +37% yearly, with large difference seasonally and between models and RCPs), and potential changes of crop production (-36% to +18% for wheat, -17% to +4% for maize, and -17% to +12% for rice, again with differences between models and RCPs), also in term of yearly variability, potentially affecting food security. The CCSM4T model projected larger changes in hydrology and reduction in crop yields than other models. Wheat was found to be more vulnerable than maize and rice to climate change
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