We evaluate links between climate and simulated river bank erosion for one of the world&a... more We evaluate links between climate and simulated river bank erosion for one of the world's largest rivers, the Mekong. We employ a process-based model to reconstruct multidecadal time series of bank erosion at study sites within the Mekong's two main hydrological response zones, defining a new parameter, accumulated excess runoff (AER), pertinent to bank erosion. We employ a hydrological model to isolate how snowmelt, tropical storms and monsoon precipitation each contribute to AER and thus modeled bank erosion. Our results show that melt (23.9% at the upstream study site, declining to 11.1% downstream) and tropical cyclones (17.5% and 26.4% at the upstream and downstream sites, respectively) both force significant fractions of bank erosion on the Mekong. We also show (i) small, but significant, declines in AER and hence assumed bank erosion during the 20th century, and; (ii) that significant correlations exist between AER and the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO). Of these modes of climate variability, we find that IOD events exert a greater control on simulated bank erosion than ENSO events; but the influences of both ENSO and IOD when averaged over several decades are found to be relatively weak. However, importantly, relationships between ENSO, IOD, and AER and hence inferred river bank erosion are not time invariant. Specifically, we show that there is an intense and prolonged epoch of strong coherence between ENSO and AER from the early 1980s to present, such that in recent decades derived Mekong River bank erosion has been more strongly affected by ENSO.
A distributed hydrological model system with a graphical user interface will be applied to Lake T... more A distributed hydrological model system with a graphical user interface will be applied to Lake Tonle Sap catchment. The main goal of the modelling project is to estimate the quantity and quality of water ending to the lake from nearby catchment areas, and thus provide input to a hydrodynamic lake model. The Lake Ton Le Sap has interesting hydrodynamics, as it is filled during monsoon time by the waters from the Mekong River, and has natural annual surface water level variation of about 7 meters. The final hydrological model system will consist of a distributed hydrological model, a graphical user interface, connections to databases, and GIS functionality. The user interface component provides model experts full access to model properties, but also enables nonexpert users to apply the system for standard computations.
Hirvi, Juha-Pekka (ed.) Operatiivinen ajelehtimis- ja kulkeutumismalli merialueille, Vesi- ja ymp... more Hirvi, Juha-Pekka (ed.) Operatiivinen ajelehtimis- ja kulkeutumismalli merialueille, Vesi- ja ympäristöhallinnon julkaisuja - sarja A ; 134, 67-76 Wind data input for the operational §D-model are obtained from the High Resolution Limited Area Model (HIRLAM). This model is at the moment the most consistent source of wind information. The Finnish meteorological institute has developed a software package for statistical interpretation of HIRLAM wind forecasts and for extracting the data. The model is, however, not able to fortecast the local features of the wiwnd field. The old wind data is archived from the last two week period. This data can be used to estimate long durated changes in the current field induced by thewind. The latest valid wind forecasts up to +48 hours are also archived. The wind data is archived from the Gulf of Finland and the Gulf of Bothnia, Northern Baltic Sea down to the Isle of Gotland. The area consist of 85 grid squares and 122 grid points. The software is a...
In: IMEMS 2004 : the seventh International Marine Environmental Modeling Seminar, Washington. D.C... more In: IMEMS 2004 : the seventh International Marine Environmental Modeling Seminar, Washington. D.C., USA, October 19-21, 2004 : proceedings. Oslo, SINTEF. P. 67 (printed abstract), P. 29-44 (full text). [CD-ROM] seventh International Marine Environmental Modeling Seminar, Washington. D.C., USA, October 19-21, 2004
ABSTRACT The effect of the grid cell size on a distributed hydrological model performance was inv... more ABSTRACT The effect of the grid cell size on a distributed hydrological model performance was investigated using five grid resolutions (1, 5, 10, 20 and 50 km) in a model for the Mekong Basin in Southeast Asia. Two main factors affecting computation results and related to topography and the grid cell size were identified: the terrain slope decreases and the computed drainage network gets shorter with the increasing grid cell size. The decrease of terrain slope induced a rise of the ground water table, increase in saturation overflow, slight increase in evapotranspiration and slower outflow from soil to river network. The shortening of the drainage network induced more peaked response to high discharge events. To compensate the effect of coarse grid cell size, new correction parameters were introduced to the model. The new parameterisation method improved goodness of fit to measured discharges with all coarse resolution model grids. However, almost the same level of improvement was obtained by modifying existing soil water conductivity parameters. Nevertheless, the proposed parameterisation decreases the dependence of soil water conductivity parameterisation from slope and improves the transferability of model parameterisation between different grid scales. Keywords: distributed; grid size; hydrological model; Mekong Basin
We evaluate links between climate and simulated river bank erosion for one of the world&a... more We evaluate links between climate and simulated river bank erosion for one of the world's largest rivers, the Mekong. We employ a process-based model to reconstruct multidecadal time series of bank erosion at study sites within the Mekong's two main hydrological response zones, defining a new parameter, accumulated excess runoff (AER), pertinent to bank erosion. We employ a hydrological model to isolate how snowmelt, tropical storms and monsoon precipitation each contribute to AER and thus modeled bank erosion. Our results show that melt (23.9% at the upstream study site, declining to 11.1% downstream) and tropical cyclones (17.5% and 26.4% at the upstream and downstream sites, respectively) both force significant fractions of bank erosion on the Mekong. We also show (i) small, but significant, declines in AER and hence assumed bank erosion during the 20th century, and; (ii) that significant correlations exist between AER and the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO). Of these modes of climate variability, we find that IOD events exert a greater control on simulated bank erosion than ENSO events; but the influences of both ENSO and IOD when averaged over several decades are found to be relatively weak. However, importantly, relationships between ENSO, IOD, and AER and hence inferred river bank erosion are not time invariant. Specifically, we show that there is an intense and prolonged epoch of strong coherence between ENSO and AER from the early 1980s to present, such that in recent decades derived Mekong River bank erosion has been more strongly affected by ENSO.
Abstract The Mekong River Basin in Southeast Asia is experiencing extensive hydropower developmen... more Abstract The Mekong River Basin in Southeast Asia is experiencing extensive hydropower development. Concerns have been raised about the consequences of the development for the ecosystems, livelihoods and food security in the region. The largest planned hydropower dam cascade in the basin, the Lancang-Jiang cascade, is currently under construction and already partly built into the Upper Mekong Basin, China. In this paper we assess the impact of the Lancang-Jiang cascade on downstream hydrology by using a combination of a ...
... Keywords: Lagrangian current measurement; surface drifters; surface currents; modelling; atmo... more ... Keywords: Lagrangian current measurement; surface drifters; surface currents; modelling; atmospheric forcing; Baltic ... material needed for the tests and development of numerical models ... The Seatrack Web programme has been developed mainly for oil-spill emergency purposes ...
We employ an excess shear stress model of the form E= k (tau b-tau c), where E is the erosion rat... more We employ an excess shear stress model of the form E= k (tau b-tau c), where E is the erosion rate, tau b is the boundary shear stress, and k and tau c are erodibility parameters (erodibility coefficient, k, and critical shear stress, tau c), to estimate river bank erosion at two study sites on the Lower Mekong River (LMR). The bank erosion model is parameterized using field measurements and analytical modeling for a wide range of flows, such that tau b can be linked to flow discharge. The bank erosion model is then forced ...
We evaluate links between climate and simulated river bank erosion for one of the world&a... more We evaluate links between climate and simulated river bank erosion for one of the world's largest rivers, the Mekong. We employ a process-based model to reconstruct multidecadal time series of bank erosion at study sites within the Mekong's two main hydrological response zones, defining a new parameter, accumulated excess runoff (AER), pertinent to bank erosion. We employ a hydrological model to isolate how snowmelt, tropical storms and monsoon precipitation each contribute to AER and thus modeled bank erosion. Our results show that melt (23.9% at the upstream study site, declining to 11.1% downstream) and tropical cyclones (17.5% and 26.4% at the upstream and downstream sites, respectively) both force significant fractions of bank erosion on the Mekong. We also show (i) small, but significant, declines in AER and hence assumed bank erosion during the 20th century, and; (ii) that significant correlations exist between AER and the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO). Of these modes of climate variability, we find that IOD events exert a greater control on simulated bank erosion than ENSO events; but the influences of both ENSO and IOD when averaged over several decades are found to be relatively weak. However, importantly, relationships between ENSO, IOD, and AER and hence inferred river bank erosion are not time invariant. Specifically, we show that there is an intense and prolonged epoch of strong coherence between ENSO and AER from the early 1980s to present, such that in recent decades derived Mekong River bank erosion has been more strongly affected by ENSO.
A distributed hydrological model system with a graphical user interface will be applied to Lake T... more A distributed hydrological model system with a graphical user interface will be applied to Lake Tonle Sap catchment. The main goal of the modelling project is to estimate the quantity and quality of water ending to the lake from nearby catchment areas, and thus provide input to a hydrodynamic lake model. The Lake Ton Le Sap has interesting hydrodynamics, as it is filled during monsoon time by the waters from the Mekong River, and has natural annual surface water level variation of about 7 meters. The final hydrological model system will consist of a distributed hydrological model, a graphical user interface, connections to databases, and GIS functionality. The user interface component provides model experts full access to model properties, but also enables nonexpert users to apply the system for standard computations.
Hirvi, Juha-Pekka (ed.) Operatiivinen ajelehtimis- ja kulkeutumismalli merialueille, Vesi- ja ymp... more Hirvi, Juha-Pekka (ed.) Operatiivinen ajelehtimis- ja kulkeutumismalli merialueille, Vesi- ja ympäristöhallinnon julkaisuja - sarja A ; 134, 67-76 Wind data input for the operational §D-model are obtained from the High Resolution Limited Area Model (HIRLAM). This model is at the moment the most consistent source of wind information. The Finnish meteorological institute has developed a software package for statistical interpretation of HIRLAM wind forecasts and for extracting the data. The model is, however, not able to fortecast the local features of the wiwnd field. The old wind data is archived from the last two week period. This data can be used to estimate long durated changes in the current field induced by thewind. The latest valid wind forecasts up to +48 hours are also archived. The wind data is archived from the Gulf of Finland and the Gulf of Bothnia, Northern Baltic Sea down to the Isle of Gotland. The area consist of 85 grid squares and 122 grid points. The software is a...
In: IMEMS 2004 : the seventh International Marine Environmental Modeling Seminar, Washington. D.C... more In: IMEMS 2004 : the seventh International Marine Environmental Modeling Seminar, Washington. D.C., USA, October 19-21, 2004 : proceedings. Oslo, SINTEF. P. 67 (printed abstract), P. 29-44 (full text). [CD-ROM] seventh International Marine Environmental Modeling Seminar, Washington. D.C., USA, October 19-21, 2004
ABSTRACT The effect of the grid cell size on a distributed hydrological model performance was inv... more ABSTRACT The effect of the grid cell size on a distributed hydrological model performance was investigated using five grid resolutions (1, 5, 10, 20 and 50 km) in a model for the Mekong Basin in Southeast Asia. Two main factors affecting computation results and related to topography and the grid cell size were identified: the terrain slope decreases and the computed drainage network gets shorter with the increasing grid cell size. The decrease of terrain slope induced a rise of the ground water table, increase in saturation overflow, slight increase in evapotranspiration and slower outflow from soil to river network. The shortening of the drainage network induced more peaked response to high discharge events. To compensate the effect of coarse grid cell size, new correction parameters were introduced to the model. The new parameterisation method improved goodness of fit to measured discharges with all coarse resolution model grids. However, almost the same level of improvement was obtained by modifying existing soil water conductivity parameters. Nevertheless, the proposed parameterisation decreases the dependence of soil water conductivity parameterisation from slope and improves the transferability of model parameterisation between different grid scales. Keywords: distributed; grid size; hydrological model; Mekong Basin
We evaluate links between climate and simulated river bank erosion for one of the world&a... more We evaluate links between climate and simulated river bank erosion for one of the world's largest rivers, the Mekong. We employ a process-based model to reconstruct multidecadal time series of bank erosion at study sites within the Mekong's two main hydrological response zones, defining a new parameter, accumulated excess runoff (AER), pertinent to bank erosion. We employ a hydrological model to isolate how snowmelt, tropical storms and monsoon precipitation each contribute to AER and thus modeled bank erosion. Our results show that melt (23.9% at the upstream study site, declining to 11.1% downstream) and tropical cyclones (17.5% and 26.4% at the upstream and downstream sites, respectively) both force significant fractions of bank erosion on the Mekong. We also show (i) small, but significant, declines in AER and hence assumed bank erosion during the 20th century, and; (ii) that significant correlations exist between AER and the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO). Of these modes of climate variability, we find that IOD events exert a greater control on simulated bank erosion than ENSO events; but the influences of both ENSO and IOD when averaged over several decades are found to be relatively weak. However, importantly, relationships between ENSO, IOD, and AER and hence inferred river bank erosion are not time invariant. Specifically, we show that there is an intense and prolonged epoch of strong coherence between ENSO and AER from the early 1980s to present, such that in recent decades derived Mekong River bank erosion has been more strongly affected by ENSO.
Abstract The Mekong River Basin in Southeast Asia is experiencing extensive hydropower developmen... more Abstract The Mekong River Basin in Southeast Asia is experiencing extensive hydropower development. Concerns have been raised about the consequences of the development for the ecosystems, livelihoods and food security in the region. The largest planned hydropower dam cascade in the basin, the Lancang-Jiang cascade, is currently under construction and already partly built into the Upper Mekong Basin, China. In this paper we assess the impact of the Lancang-Jiang cascade on downstream hydrology by using a combination of a ...
... Keywords: Lagrangian current measurement; surface drifters; surface currents; modelling; atmo... more ... Keywords: Lagrangian current measurement; surface drifters; surface currents; modelling; atmospheric forcing; Baltic ... material needed for the tests and development of numerical models ... The Seatrack Web programme has been developed mainly for oil-spill emergency purposes ...
We employ an excess shear stress model of the form E= k (tau b-tau c), where E is the erosion rat... more We employ an excess shear stress model of the form E= k (tau b-tau c), where E is the erosion rate, tau b is the boundary shear stress, and k and tau c are erodibility parameters (erodibility coefficient, k, and critical shear stress, tau c), to estimate river bank erosion at two study sites on the Lower Mekong River (LMR). The bank erosion model is parameterized using field measurements and analytical modeling for a wide range of flows, such that tau b can be linked to flow discharge. The bank erosion model is then forced ...
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Papers by Hannu Lauri