ABSTRACT The degree of land surface-subsurface coupling is controlled by complex interactions bet... more ABSTRACT The degree of land surface-subsurface coupling is controlled by complex interactions between the atmosphere, land surface condition and subsurface hydrologic characteristics. Global climate models project increases in temperature and changes in precipitation rates and patterns which in turn alter terrestrial water and energy budgets impacting water resources. However, the degree of land surface-subsurface coupling under scenarios of land cover and climate change has not been fully explored. In this study, we used an integrated groundwater-surface water-land surface model (ParFlow.CLM) across a semi-arid catchment located in the central west New South Wales, Australia to assess variability in water and energy fluxes under historic condition and scenarios of climate and land cover change. The Baldry hydrological observatory situated in a topographically flat terrain has the area of 2 km2 and contains two distinct land cover types of pasture and a regenerated Eucalyptus forest. High resolution groundwater level measurements in the site reveal differences in groundwater connectivity in wet versus dry periods in pasture and Eucalyptus forest for the historic condition. Using downscaled climate forcing obtained from a regional climate model for eastern Australia, the degree of land surface-subsurface coupling within the catchment was examined under various scenarios of climate and changes in land cover types. It is expected that a fully integrated hydrologic model like ParFlow.CLM improve predictions in land-atmospheric feedback processes under changes in hydrologic conditions.
Quantifying spatial and temporal variability of riparian evapotranspiration (ET) is essential in ... more Quantifying spatial and temporal variability of riparian evapotranspiration (ET) is essential in water resources management especially in management and restoration of riparian ecosystems where multiple agricultural, industrial, and domestic users may exist. To enhance riparian evapotranspiration estimation in a MODFLOW groundwater model, RIPGIS-NET, an ArcGIS custom application, was developed to derive parameters and visualize results of spatially explicit riparian evapotranspiration in groundwater flow models for ecohydrology, riparian ecosystem management, stream restoration and water resources applications. RIPGIS-NET works with RIP-ET, a modeling package for MODFLOW. RIP-ET improves riparian ET simulations by using a set of eco-physiologically based ET curves for plant functional subgroups (PFSG), and is able to separate ground evaporation and plant transpiration processes. To evaluate impact of riparian restoration scenarios on groundwater resources, the above packages were applied to MODFLOW model of hypothetical Dry Alkaline Valley area. Using riparian ET curve files which show the relation between the groundwater level and ET, aerial extent of riparian vegetation in each season and a digital elevation map, RIPGIS-NET derived RIP-ET model parameters for each season. After running MODFLOW, groundwater head dynamics and spatial variability of riparian ET were visualized in GIS environment for each restoration scenario. This study provided useful information for riparian restoration planning in this area. It further highlighted the advantage of using spatially explicit models and datasets for riparian restoration planning.
ABSTRACT Long-duration high-volume dam releases are unique anthropogenic events with no naturally... more ABSTRACT Long-duration high-volume dam releases are unique anthropogenic events with no naturally occurring equivalents. The impact from such dam releases on a downstream Quaternary alluvial aquifer in New South Wales, Australia, is assessed. It is observed that long-duration (> 26 days), high-volume dam releases (> 8,000 ML/day average) result in significant variations in river-aquifer interactions. These variations include a flux from the river to the aquifer up to 6.3 m(3)/day per metre of bank (at distances of up to 330 m from the river bank), increased extent and volume of recharge/bank storage, and a long-term (> 100 days) reversal of river-aquifer fluxes. In contrast, during lower-volume events (< 2,000 ML/day average) the flux was directed from the aquifer to the river at rates of up to 1.6 m(3)/day per metre of bank. A groundwater-head prediction model was constructed and river-aquifer fluxes were calculated; however, predicted fluxes from this method showed poor correlation to fluxes calculated using actual groundwater heads. Long-duration high-volume dam releases have the potential to skew estimates of long-term aquifer resources and detrimentally alter the chemical and physical properties of phreatic aquifers flanking the river. The findings have ramifications for improved integrated management of dam systems and downstream aquifers.
ABSTRACT One of the main challenges in the application of coupled or integrated hydrologic models... more ABSTRACT One of the main challenges in the application of coupled or integrated hydrologic models is specifying a catchment's initial conditions in terms of soil moisture and depth-to-water table (DTWT) distributions. One approach to reducing uncertainty in model initialization is to run the model recursively using either a single year or multiple years of forcing data until the system equilibrates with respect to state and diagnostic variables. However, such "spin-up" approaches often require many years of simulations, making them computationally intensive. In this study, a new hybrid approach was developed to reduce the computational burden of the spin-up procedure by using a combination of model simulations and an empirical DTWT function. The methodology is examined across two distinct catchments located in a temperate region of Denmark and a semi-arid region of Australia. Our results illustrate that the hybrid approach reduced the spin-up period required for an integrated groundwater–surface water–land surface model (ParFlow.CLM) by up to 50%. To generalize results to different climate and catchment conditions, we outline a methodology that is applicable to other coupled or integrated modeling frameworks when initialization from an equilibrium state is required.
ABSTRACT The degree of land surface-subsurface coupling is controlled by complex interactions bet... more ABSTRACT The degree of land surface-subsurface coupling is controlled by complex interactions between the atmosphere, land surface condition and subsurface hydrologic characteristics. Global climate models project increases in temperature and changes in precipitation rates and patterns which in turn alter terrestrial water and energy budgets impacting water resources. However, the degree of land surface-subsurface coupling under scenarios of land cover and climate change has not been fully explored. In this study, we used an integrated groundwater-surface water-land surface model (ParFlow.CLM) across a semi-arid catchment located in the central west New South Wales, Australia to assess variability in water and energy fluxes under historic condition and scenarios of climate and land cover change. The Baldry hydrological observatory situated in a topographically flat terrain has the area of 2 km2 and contains two distinct land cover types of pasture and a regenerated Eucalyptus forest. High resolution groundwater level measurements in the site reveal differences in groundwater connectivity in wet versus dry periods in pasture and Eucalyptus forest for the historic condition. Using downscaled climate forcing obtained from a regional climate model for eastern Australia, the degree of land surface-subsurface coupling within the catchment was examined under various scenarios of climate and changes in land cover types. It is expected that a fully integrated hydrologic model like ParFlow.CLM improve predictions in land-atmospheric feedback processes under changes in hydrologic conditions.
ABSTRACT The degree of land surface-subsurface coupling is controlled by complex interactions bet... more ABSTRACT The degree of land surface-subsurface coupling is controlled by complex interactions between the atmosphere, land surface condition and subsurface hydrologic characteristics. Global climate models project increases in temperature and changes in precipitation rates and patterns which in turn alter terrestrial water and energy budgets impacting water resources. However, the degree of land surface-subsurface coupling under scenarios of land cover and climate change has not been fully explored. In this study, we used an integrated groundwater-surface water-land surface model (ParFlow.CLM) across a semi-arid catchment located in the central west New South Wales, Australia to assess variability in water and energy fluxes under historic condition and scenarios of climate and land cover change. The Baldry hydrological observatory situated in a topographically flat terrain has the area of 2 km2 and contains two distinct land cover types of pasture and a regenerated Eucalyptus forest. High resolution groundwater level measurements in the site reveal differences in groundwater connectivity in wet versus dry periods in pasture and Eucalyptus forest for the historic condition. Using downscaled climate forcing obtained from a regional climate model for eastern Australia, the degree of land surface-subsurface coupling within the catchment was examined under various scenarios of climate and changes in land cover types. It is expected that a fully integrated hydrologic model like ParFlow.CLM improve predictions in land-atmospheric feedback processes under changes in hydrologic conditions.
Quantifying spatial and temporal variability of riparian evapotranspiration (ET) is essential in ... more Quantifying spatial and temporal variability of riparian evapotranspiration (ET) is essential in water resources management especially in management and restoration of riparian ecosystems where multiple agricultural, industrial, and domestic users may exist. To enhance riparian evapotranspiration estimation in a MODFLOW groundwater model, RIPGIS-NET, an ArcGIS custom application, was developed to derive parameters and visualize results of spatially explicit riparian evapotranspiration in groundwater flow models for ecohydrology, riparian ecosystem management, stream restoration and water resources applications. RIPGIS-NET works with RIP-ET, a modeling package for MODFLOW. RIP-ET improves riparian ET simulations by using a set of eco-physiologically based ET curves for plant functional subgroups (PFSG), and is able to separate ground evaporation and plant transpiration processes. To evaluate impact of riparian restoration scenarios on groundwater resources, the above packages were applied to MODFLOW model of hypothetical Dry Alkaline Valley area. Using riparian ET curve files which show the relation between the groundwater level and ET, aerial extent of riparian vegetation in each season and a digital elevation map, RIPGIS-NET derived RIP-ET model parameters for each season. After running MODFLOW, groundwater head dynamics and spatial variability of riparian ET were visualized in GIS environment for each restoration scenario. This study provided useful information for riparian restoration planning in this area. It further highlighted the advantage of using spatially explicit models and datasets for riparian restoration planning.
ABSTRACT Long-duration high-volume dam releases are unique anthropogenic events with no naturally... more ABSTRACT Long-duration high-volume dam releases are unique anthropogenic events with no naturally occurring equivalents. The impact from such dam releases on a downstream Quaternary alluvial aquifer in New South Wales, Australia, is assessed. It is observed that long-duration (> 26 days), high-volume dam releases (> 8,000 ML/day average) result in significant variations in river-aquifer interactions. These variations include a flux from the river to the aquifer up to 6.3 m(3)/day per metre of bank (at distances of up to 330 m from the river bank), increased extent and volume of recharge/bank storage, and a long-term (> 100 days) reversal of river-aquifer fluxes. In contrast, during lower-volume events (< 2,000 ML/day average) the flux was directed from the aquifer to the river at rates of up to 1.6 m(3)/day per metre of bank. A groundwater-head prediction model was constructed and river-aquifer fluxes were calculated; however, predicted fluxes from this method showed poor correlation to fluxes calculated using actual groundwater heads. Long-duration high-volume dam releases have the potential to skew estimates of long-term aquifer resources and detrimentally alter the chemical and physical properties of phreatic aquifers flanking the river. The findings have ramifications for improved integrated management of dam systems and downstream aquifers.
ABSTRACT One of the main challenges in the application of coupled or integrated hydrologic models... more ABSTRACT One of the main challenges in the application of coupled or integrated hydrologic models is specifying a catchment's initial conditions in terms of soil moisture and depth-to-water table (DTWT) distributions. One approach to reducing uncertainty in model initialization is to run the model recursively using either a single year or multiple years of forcing data until the system equilibrates with respect to state and diagnostic variables. However, such "spin-up" approaches often require many years of simulations, making them computationally intensive. In this study, a new hybrid approach was developed to reduce the computational burden of the spin-up procedure by using a combination of model simulations and an empirical DTWT function. The methodology is examined across two distinct catchments located in a temperate region of Denmark and a semi-arid region of Australia. Our results illustrate that the hybrid approach reduced the spin-up period required for an integrated groundwater–surface water–land surface model (ParFlow.CLM) by up to 50%. To generalize results to different climate and catchment conditions, we outline a methodology that is applicable to other coupled or integrated modeling frameworks when initialization from an equilibrium state is required.
ABSTRACT The degree of land surface-subsurface coupling is controlled by complex interactions bet... more ABSTRACT The degree of land surface-subsurface coupling is controlled by complex interactions between the atmosphere, land surface condition and subsurface hydrologic characteristics. Global climate models project increases in temperature and changes in precipitation rates and patterns which in turn alter terrestrial water and energy budgets impacting water resources. However, the degree of land surface-subsurface coupling under scenarios of land cover and climate change has not been fully explored. In this study, we used an integrated groundwater-surface water-land surface model (ParFlow.CLM) across a semi-arid catchment located in the central west New South Wales, Australia to assess variability in water and energy fluxes under historic condition and scenarios of climate and land cover change. The Baldry hydrological observatory situated in a topographically flat terrain has the area of 2 km2 and contains two distinct land cover types of pasture and a regenerated Eucalyptus forest. High resolution groundwater level measurements in the site reveal differences in groundwater connectivity in wet versus dry periods in pasture and Eucalyptus forest for the historic condition. Using downscaled climate forcing obtained from a regional climate model for eastern Australia, the degree of land surface-subsurface coupling within the catchment was examined under various scenarios of climate and changes in land cover types. It is expected that a fully integrated hydrologic model like ParFlow.CLM improve predictions in land-atmospheric feedback processes under changes in hydrologic conditions.
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Papers by Hoori Ajami