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  • Hydrology
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  • 1
    Language: English
    Description: Study region Nyangores River watershed, headwater catchment of Mara River basin in Kenya. Study focus Climate variability and human activities are the main drivers of change of watershed hydrology. The contribution of climate variability and land use change to change in streamflow of Nyangores River, was investigated. Mann Kendall and sequential Mann Kendall tests were used to investigate the presence and breakpoint of a trend in discharge data (1965–2007) respectively. The Budyko framework was used to separate the respective contribution of drivers to change in discharge. Future response of the watershed to climate change was predicted using the runoff sensitivity equation developed. New hydrological insights for the region There was a significant increasing trend in the discharge with a breakpoint in 1977. Land use change was found to be the main driver of change in discharge accounting for 97.5% of the change. Climate variability only caused a net increase of the remaining 2.5% of the change; which was caused by counter impacts on discharge of increase in rainfall (increased discharge by 24%) and increase in potential evapotranspiration (decreased discharge by 21.5%). Climate change was predicted to cause a moderate 16% and 15% increase in streamflow in the next 20 and 50 years respectively. Change in discharge was specifically attributed to deforestation at the headwaters of the watershed.
    Keywords: Info:Eu-Repo/Classification/Ddc/690 ; Ddc:690 ; Klimavariabilität ; Landnutzungsänderung ; Hydrologie ; Streamflow ; Wassersicherheit ; Budyko Rahmen ; Technische Universität Dresden ; Publikationsfonds ; Climate Variability ; Land Use Change ; Hydrology ; Streamflow ; Water Security ; Budyko Framework ; Technische Universität Dresden ; Publishing Fund
    Source: Networked Digital Library of Theses and Dissertations
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  • 2
    Language: English
    In: Journal of Hydrology: Regional Studies, March 2016, Vol.5, pp.244-260
    Description: Nyangores River watershed, headwater catchment of Mara River basin in Kenya. Climate variability and human activities are the main drivers of change of watershed hydrology. The contribution of climate variability and land use change to change in streamflow of Nyangores River, was investigated. Mann Kendall and sequential Mann Kendall tests were used to investigate the presence and breakpoint of a trend in discharge data (1965–2007) respectively. The Budyko framework was used to separate the respective contribution of drivers to change in discharge. Future response of the watershed to climate change was predicted using the runoff sensitivity equation developed. There was a significant increasing trend in the discharge with a breakpoint in 1977. Land use change was found to be the main driver of change in discharge accounting for 97.5% of the change. Climate variability only caused a net increase of the remaining 2.5% of the change; which was caused by counter impacts on discharge of increase in rainfall (increased discharge by 24%) and increase in potential evapotranspiration (decreased discharge by 21.5%). Climate change was predicted to cause a moderate 16% and 15% increase in streamflow in the next 20 and 50 years respectively. Change in discharge was specifically attributed to deforestation at the headwaters of the watershed.
    Keywords: Climate Variability ; Land Use Change ; Hydrology ; Streamflow ; Water Security ; Budyko Framework ; Geography
    ISSN: 2214-5818
    E-ISSN: 2214-5818
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  • 3
    In: Hydrological Processes, 30 August 2016, Vol.30(18), pp.3139-3155
    Description: Land‐use change is one of the main drivers of watershed hydrology change. The effect of forestry related land‐use changes (e.g. afforestation, deforestation, agroforestry) on water fluxes depends on climate, watershed characteristics and spatial scale. The Soil and Water Assessment Tool (SWAT) model was calibrated, validated and used to simulate the impact of agroforestry on the water balance in the Mara River Basin (MRB) in East Africa. Model performance was assessed by Nash–Sutcliffe Efficiency (NSE) and Kling–Gupta Efficiency (KGE). The NSE (and KGE) values for calibration and validation were: 0.77 (0.88) and 0.74 (0.85) for the Nyangores sub‐watershed, and 0.78 (0.89) and 0.79 (0.63) for the entire MRB. It was found that agroforestry in the watershed would generally reduce surface runoff, mainly because of enhanced infiltration. However, it would also increase evapotranspiration and consequently reduce baseflow and overall water yield, which was attributed to increased water use by trees. Spatial scale was found to have a significant effect on water balance; the impact of agroforestry was higher at the smaller headwater catchment (Nyangores) than for the larger watershed (entire MRB). However, the rate of change in water yield with an increase in area under agroforestry was different for the two and could be attributed to the spatial variability of climate within the MRB. Our results suggest that direct extrapolation of the findings from a small sub‐catchment to a larger watershed may not always be accurate. These findings could guide watershed managers on the level of trade‐offs that might occur between reduced water yields and other benefits (e.g. soil erosion control, improved soil productivity) offered by agroforestry. Copyright © 2016 John Wiley & Sons, Ltd.
    Keywords: Land‐Use ; Agroforestry ; Swat Model ; Hydrology ; Catchment Water Balance
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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  • 4
    Language: English
    In: Journal of Earth Science, 2010, Vol.21(6), pp.974-978
    Description: Land-cover changes cause a loss of natural vegetation in many parts of the world. In the Xishuangbanna (西双版纳) district (Yunnan (云南) Province), rubber plantations replace tropical rainforests covering already an area of about 10% of the study area (2007). There, land-use allocation is mostly driven by economic considerations. Thus, local planning authorities need decision support for land-use planning issues, which integrate socio-economic and ecological aspects. Within the NabanFrame, an agro-economic, ecological and social model was applied, which, altogether, interacted with a land allocation model via defined interfaces. Effects on the water cycle, ecological conditions as well as socio-economic should be considered by integrating the spatially distributed rainfall-runoff and water balance model AKWA-M® in the model setup.
    Keywords: land-use ; water balance model ; rubber ; integrated land-use planning ; land-use prognosis
    ISSN: 1674-487X
    E-ISSN: 1867-111X
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  • 5
    Language: English
    In: Geoderma, 15 February 2016, Vol.264, pp.350-362
    Description: Data scarcity represents a serious limitation to the use of hydrologic models for supporting decision making processes, and may lead to inappropriate measures for integrated water resources management efforts. In particular, the importance of spatially distributed soil information is often overlooked. The forest-dominated Águeda catchment in north-central Portugal is an example of a region with serious soil data availability limitations. The Soil Land Inference Model (SoLIM) approach, combined with information from several soil surveys, was used to create a map of soil properties based upon the effective soil depths of the landscape. The modified soil map provided a better representation of the soil spatial attributes, particularly the distribution of soil water content. The Soil Water Assessment Tool (SWAT) was applied to the Águeda catchment with two input data sets differing in the soil data. Although SWAT performed satisfactorily in simulating daily streamflow for both data sets at the outlet, results of our study indicate that the SoLIM derived soil data set provides a better representation of the first peak flow events after the dry period. Additionally, it is shown that the better representation of profile depth can contribute considerably to the understanding of water balance components at the small scale and for the implications for management. This study underlines the importance of spatially distributed soil information in watershed modeling for decision making in the river basin management process.
    Keywords: Digital Soil Mapping ; Soil Variation ; Solim ; Hydrological Modeling ; SWAT ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 6
    Language: English
    In: Forest Ecology and Management, 2009, Vol.258(10), pp.2163-2174
    Description: Knowledge of site-specific water conditions is important in forestland evaluation and fundamental for a sustainable forest management. In Central Europe, traditional site mapping has followed an integrated ecological approach. The assessment of soil water availability is based on overlaying relief and descriptive soil information. It is a relative system referring to an (hypothetical) equilibrium between relief-dependent soil conditions and the potential natural forest association at a given regional climate. Accordingly, the climatic settings are supposed to be constant and are mostly based on long-term means of precipitation and air temperature. However, long-term climate changes, as well as infrequent climatic extremes have not been considered adequately. Furthermore, the feedback of forest management itself on available soil water cannot be addressed. To overcome these shortcomings, we developed an approach in which the soil hydrological model LWF-BROOK90 is organized in a GIS-frame to simulate the daily water fluxes and soil moisture status. Spatially distributed meteorological input data is generated from long-term station data using special regionalization procedures. Model parameterization for soil physical properties by horizon are derived from detailed forest soil maps using pedotransfer functions. Thus, we obtained data on all components of the water balance depending on climate, aspect, slope, vertical soil properties, and stand conditions in a spatial resolution of 25 m × 25 m. In addition to the common output of site water balance models, additional indicators were implemented to enable the quantification of ‘transpiration stress’, ‘soil drought stress’, and ‘excess soil water stress’. Soil water evaluation is based on the number of days exceeding defined thresholds of parameter values. The implemented soil water indices were suitable to reflect relevant differences in the soil water conditions between sites whereas focusing on individual and extreme years rather than on long-term averages seems to be more appropriate for assessing water-related tree growth conditions. The next step will be to produce forest site maps based on such ‘stress’ indicators. The novel approach provides a more objective description of variable soil water conditions than the currently used mapping approach. Furthermore, it makes spatial hydrological data (e.g. groundwater recharge) available for use beyond forest management.
    Keywords: Forest Site Mapping ; Forest Site Evaluation ; Forest Climatology ; Soil Water Modelling ; Eco-Hydrology ; Hydropedology ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 7
    Language: English
    In: Journal of Plant Nutrition and Soil Science, August 2016, Vol.179(4), pp.425-438
    Description: Understanding and quantification of phosphorus (P) fluxes are key requirements for predictions of future forest ecosystems changes as well as for transferring lessons learned from natural ecosystems to croplands and plantations. This review summarizes and evaluates the recent knowledge on mechanisms, magnitude, and relevance by which dissolved and colloidal inorganic and organic P forms can be translocated within or exported from forest ecosystems. Attention is paid to hydrological pathways of P losses at the soil profile and landscape scales, and the subsequent influence of P on aquatic ecosystems. New (unpublished) data from the German Priority Program 1685 “” were added to provide up‐to‐date flux‐based information. Nitrogen (N) additions increase the release of water‐transportable P forms. Most P found in percolates and pore waters belongs to the so‐called dissolved organic P (DOP) fractions, rich in orthophosphate‐monoesters and also containing some orthophosphate‐diesters. Total solution P concentrations range from ca. 1 to 400 µg P L, with large variations among forest stands. Recent sophisticated analyses revealed that large portions of the DOP in forest stream water can comprise natural nanoparticles and fine colloids which under extreme conditions may account for 40–100% of the P losses. Their translocation within preferential flow passes may be rapid, mediated by storm events. The potential total P loss through leaching into subsoils and with streams was found to be less than 50 mg P m a, suggesting effects on ecosystems at centennial to millennium scale. All current data are based on selected snapshots only. Quantitative measurements of P fluxes in temperate forest systems are nearly absent in the literature, probably due to main research focus on the C and N cycles. Therefore, we lack complete ecosystem‐based assessments of dissolved and colloidal P fluxes within and from temperate forest systems.
    Keywords: Forest Ecosystem ; Phosphorus ; Fluxes ; Soil ; Processes ; Hydrology
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 8
    Language: English
    In: Biogeochemistry, 2003, Vol.65(3), pp.341-368
    Description: The biogeochemical input-output fluxes of two forested catchments with contrasting levels of atmospheric deposition were investigated in Germany. This paper focuses on the effects of recent changes in atmospheric inputs on the chemical composition in the soil solution and stream. The catchment 'Schluchsee' (Black Forest; SW Germany) is characterized by relatively low atmospheric inputs whereas 'Rotherdbach' (Ore Mountains; E Germany) received significant amounts of acid deposition (mainly originating from SO 2 emissions) until recent years. Both sites reveal decreases in H + and S deposition during the 1990s. This pattern is typical when compared to trends in Europe. In response to the reduced S deposition, soil solution and streamwater SO 4 2− concentrations decreased significantly. A net release of SO 4 2− (output 〉 input) was observed at both sites due to the release of S previously stored in the soil. The level of N deposition was more or less constant at both sites. At Schluchsee, NO 3 − concentration in streamwater remained more or less unchanged, whereas a decrease at Rotherdbach was observed. A recovery from acidification was found in seepage water as indicated by increasing acid neutralizing capacity (ANC). Streamwater ANC increased only in the permanently acidified Rotherdbach. No change of ANC was observed in the Schluchsee stream, which was characterized by episodic acidification during high-flow conditions. Nevertheless, the key factor controlling the recovery from surface water acidification was the type, amount and distribution of stored S pools in the ecosystem. Thus, time series analysis of long-term data of input-output chemistry can be a valuable instrument in order to improve the understanding of linked terrestrial-aquatic systems and give useful clues for modeling efforts.
    Keywords: Atmospheric deposition ; Forested catchments ; Norway spruce ; Recovery from acidification ; Soil leachate ; Streamwater
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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  • 9
    Language: English
    Description: Study region Nyangores River watershed, headwater catchment of Mara River basin in Kenya. Study focus Climate variability and human activities are the main drivers of change of watershed hydrology. The contribution of climate variability and land use change to change in streamflow of Nyangores River, was investigated. Mann Kendall and sequential Mann Kendall tests were used to investigate the presence and breakpoint of a trend in discharge data (1965–2007) respectively. The Budyko framework was used to separate the respective contribution of drivers to change in discharge. Future response of the watershed to climate change was predicted using the runoff sensitivity equation developed. New hydrological insights for the region There was a significant increasing trend in the discharge with a breakpoint in 1977. Land use change was found to be the main driver of change in discharge accounting for 97.5% of the change. Climate variability only caused a net increase of the remaining 2.5% of the change; which was caused by counter impacts on discharge of increase in rainfall (increased discharge by 24%) and increase in potential evapotranspiration (decreased discharge by 21.5%). Climate change was predicted to cause a moderate 16% and 15% increase in streamflow in the next 20 and 50 years respectively. Change in discharge was specifically attributed to deforestation at the headwaters of the watershed.
    Keywords: Klimavariabilität ; Landnutzungsänderung ; Hydrologie ; Streamflow ; Wassersicherheit ; Budyko Rahmen ; Technische Universität Dresden ; Publikationsfonds ; Climate Variability ; Land Use Change ; Hydrology ; Streamflow ; Water Security ; Budyko Framework ; Technische Universität Dresden ; Publishing Fund ; Ddc:690 ; Rvk:Zi 0001
    Source: Networked Digital Library of Theses and Dissertations
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  • 10
    Language: English
    Description: Land use change and climate variability are the main drivers of watershed hydrological processes. The main objective of this study was to assess the impact of land use change and climate variability on hydrology of the Mara River Basin in East Africa. Land use maps generated from satellite images were analyzed using the intensity analysis approach to determine the patterns, dynamics and intensity of land use change. Changes in measured streamflow caused separately by land use change and climate variability were separated using the catchment water-energy budget based approach of Budyko framework. The information on past impact of climate variability on streamflow was used to develop a runoff sensitivity equation which was then used to predict the future impact of climate change on streamflow. Finally, the impact of agroforestry on watershed water balance was predicted using SWAT (Soil and Water Assessment Tool) model. Deforestation and expansion of agriculture were found to be dominant and intensive land use changes in the watershed. The deforestation was attributed to illegal encroachment and excision of the forest reserve. The deforested land was mainly converted to small scale agriculture particularly in the headwaters of the watershed. There was intensive conversion of rangeland to largescale mechanized agriculture which accelerated with change of land tenure (privatization). The watershed has a very dynamic land use change as depicted by swap change (simultaneous equal loss and gains of a particular land use/cover) which accounted for more than half of the overall change. This implies that reporting only net change in land use (of MRB) underestimates the total land use change. The results show that streamflow of Nyangores River (a headwater tributary of the Mara River) significantly increased over the last 50 years. Land use change (particularly deforestation) contributed 97.5% of change in streamflow while the rest of the change (2.5%) was caused by climate variability. It was predicted that climate change would cause a moderate 15% increase in streamflow in the next 50 years. SWAT model simulations suggested that implementation of agroforestry in the watershed would reduce surface runoff, mainly due expected improvement of soil infiltration. Baseflow and total water yield would also decrease while evapotranspiration would increase. The changes in baseflow (reduction) and evapotranspiration (increase) were attributed to increased water extraction from the soil and groundwater by trees in agroforestry systems. The impact of agroforestry on water balance (surface runoff, baseflow, water yield and evapotranspiration) was proportional to increase in size of the watershed simulated with agroforestry. Modelling results also suggested that climate variability within the watershed has a profound effect on the change of water balance caused by implementation of agroforestry. It is recommended that authorities should pay more attention to land use change as the main driver of change in watershed hydrology of the basin. More effort should be focused on prevention of further deforestation and agroforestry may be considered as a practical management strategy to reverse/reduce degradation on the deforested parts of the watershed currently under intensive cultivation.
    Keywords: Info:Eu-Repo/Classification/Ddc/550 ; Ddc:550 ; Hydrologie ; Hydrology ; Climate Variability
    Source: Networked Digital Library of Theses and Dissertations
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