David Gustafsson | KTH Royal Institute of Technology (original) (raw)

Papers by David Gustafsson

Research for Policy and Practice, 2012

ABSTRACT Near surface climate was observed through temperature profiling from the surface to 2.47... more ABSTRACT Near surface climate was observed through temperature profiling from the surface to 2.47 m height in an urban vegetated park and its surroundings in central Stockholm, Sweden. Measurements were conducted during three summer days by mobile traverses. Air temperature differences between the built-up area and the park were in the range of 0.5–0.8 °C during the day and reached a maximum of 2 °C at sunset. The thermal stratification of the air was mainly stable in the park and unstable in the built-up area. Inverse air temperature profiles in the park were less stable in open than in shady areas, and close to neutral at midday. The most unstable air was found in the north–south orientated canyons in the early afternoon. Possible heat advection from the surroundings, and thus uncoupling between the surface and the air, was identified through temperature gradients pointing at different directions within the 2.47 m profile. Examples at midday indicated that warm air advected as far as 150 m into the park.

Theoretical and Applied Climatology, 2001

We compared two one-dimensional simulation models for heat and water¯uxes in the soil-snow-atmosp... more We compared two one-dimensional simulation models for heat and water¯uxes in the soil-snow-atmosphere system with respect to their mathematical formulations of the surface heat exchange and the snow pack evolution. They were chosen as examples of a simple one-layer snow model and a more detailed multiple-layer snow model (SNTHERM). The snow models were combined with the same one-dimensional model for the heat and water balance of the underlying soil (CoupModel). Data from an arable ®eld in central Sweden (Marsta), covering two years (1997±1999) of soil temperature, snow depth and eddy-correlation measurements were successfully compared with the models. Conditions with a snow pack deeper or shallower than 10 cm and bare soil resulted in similar discrepancies. The simulated net radiation and sensible heat¯ux were in good agreement with that measured during snow-covered periods, except for situations with snowmelt when the downward sensible heat¯ux was overestimated by 10±20 Wm À2 . The results showed that the uncertainties in parameter values were more important than the model formulation and that both models were useful in evaluating the limitations and uncertainties of the measurements.

Journal of Geophysical Research, 2009

Journal of Applied Meteorology, 2004

ABSTRACT The water and heat balances of an arable field and a forest in the boreal zone in Scandi... more ABSTRACT The water and heat balances of an arable field and a forest in the boreal zone in Scandinavia were explored using 3 yr of observations and simulations with two different soil vegetation atmosphere transfer (SVAT) models over a 30-yr period. Results from a detailed mechanistic model [coupled heat and mass transfer model (COUP)] were compared with those obtained with a large-scale type of SVAT model used in the weather prediction model at the European Centre for Medium-Range Weather Forecasts [ECMWF tiled land surface scheme (TESSEL)]. The COUP model simulations agreed well with the observations from a seasonal perspective. The TESSEL model differed significantly from the measurements when standard operational parameter values were used. The introduction of a seasonal variation in leaf-area index values, tuned canopy resistance for forest, and a reduced roughness length over snow-covered open land reduced the discrepancies. Net radiation was 40% higher in the forest when compared with the arable land, based on 30-yr simulations with both models. Furthermore, the forest was a net source of sensible heat flux, whereas the arable land was a net sink. Because of different treatment of winter interception evaporation, forest latent heat flux based on the COUP model considerably exceeded that from the TESSEL model, and suggested that the total annual evaporation was higher from the forest than from arable land. The representation of interception evaporation in winter, as well as seasonal dynamics in vegetation properties are, thus, of considerable importance for adequate simulation of forest and arable land energy fluxes within the boreal zone.

Journal of Applied Meteorology, 2003

The objective of the present study was to assess the performance and recent improvements of the l... more The objective of the present study was to assess the performance and recent improvements of the land surface scheme used operationally in the European Centre for Medium-Range Weather Forecasts (ECMWF) in a Scandinavian boreal forest climate/ecosystem. The previous (the 1999 scheme of P. Viterbo and A. K. Betts) and the new (Tiled ECMWF Surface Scheme for Exchange Processes over Land,

Hydrology and Earth System Sciences, 2009

Ten conceptually different models in predicting discharge from the artificial Chicken Creek catch... more Ten conceptually different models in predicting discharge from the artificial Chicken Creek catchment in North-East Germany were used for this study. Soil texture and topography data were given to the modellers, but discharge data was withheld. We compare the predictions with the measurements from the 6 ha catchment and discuss the conceptualization and parameterization of the models. The predictions vary in a wide range, e.g. with the predicted actual evapotranspiration ranging from 88 to 579 mm/y and the discharge from 19 to 346 mm/y. The predicted components of the hydrological cycle deviated systematically from the observations, which were not known to the modellers. Discharge was mainly predicted as subsurface discharge with little direct runoff. In reality, surface runoff was a major flow component despite the fairly coarse soil texture. The actual evapotranspiration (AET) and the ratio between actual and potential ET was systematically overestimated by nine of the Correspondence to: H. M. Holländer (hartmut.hollaender@tu-cottbus.de) ten models. None of the model simulations came even close to the observed water balance for the entire 3-year study period. The comparison indicates that the personal judgement of the modellers was a major source of the differences between the model results. The most important parameters to be presumed were the soil parameters and the initial soilwater content while plant parameterization had, in this particular case of sparse vegetation, only a minor influence on the results.

The intersection of the developing topic of rating curve and discharge series uncertainty with th... more The intersection of the developing topic of rating curve and discharge series uncertainty with the topic of hydrological change detection (e.g., in response to land cover or climatic change) has not yet been well studied. The work herein explores this intersection, with consideration of a long-term discharge response for a~650-km 2 headwater basin of the Mara River in west Kenya, starting with stream rating and daily gauge height data. A rating model was calibrated using Bayesian methods to quantify uncertainty intervals in model parameters and predictions. There was an unknown balance of random and systemic error in rating data scatter (a scenario not likely unique to this basin), which led to an unknown balance of noise and information in the calibrated statistical error model. This had implications on testing for hydrological change. Overall, indications were that shifts in basin's discharge response were rather subtle over the 44-year period. A null hypothesis for change using flow duration curves (FDCs) from four different 8-year data intervals could be either accepted or rejected over much of the net flow domain depending on different applications of the statistical error model (each with precedence in the literature). The only unambiguous indication of change in FDC comparisons appeared to be a reduction in lowest baseflow in recent years (flows with >98% exceedance probability). We defined a subjective uncertainty interval based on an intermediate balance of random and systematic error in the rating model that suggested a possibility of more prevalent impacts. These results have relevance to management in the Mara basin and to future studies that might establish linkages to historic land use and climatic factors. The concern about uncertain uncertainty intervals (uncertainty 2 ) extends beyond the Mara and is relevant to testing change where non-random rating errors may be important and subtle responses are investigated. example, magnitudes of flows in the mid-flow region were generally less during 1964-1971 than during 1975-1982 for~40% of the total flow regime.

Hydrological Processes, 2000

Manual snow measurements are becoming increasingly expensive at the same time as climate change i... more Manual snow measurements are becoming increasingly expensive at the same time as climate change imposed snow alterations affect runoff and frost patterns; snow observations are included in runoff modelling, making reliable snow observations outmost important. Multiple new and modified ground-based techniques for monitoring snow depth, density, water equivalent (SWE), wetness, and layering have been tested over the last decade justifying a review of such methods. Techniques based on snow mass, electrical properties, attenuation of radioactivity and, other miscellaneous properties are reviewed. The following sensors seem suitable for registration of temporal variations: Ultrasonic (depth) and terrestrial laser scanning (depth), several snow pillows at the same location (SWE), CRREL/NRCS weighing sensor (SWE), Snowpower (depth, density, SWE and wetness), active and passive (cosmic) gamma-ray attenuation (SWE), and adjusted TDRprobes (density and wetness). Ground penetrating radar (GPR) is, depending on design and operation mode, suitable for different purposes; when arrays of antennas are pulled by a snowmobile the technique is suitable for monitoring of spatial variations in depth, density and SWE for dry snow. Techniques are under development which hopefully will improve the accuracy also for wet snow measurements. Frequency modulated continuous wave (FMCW) GPRs seem fit for measurement of snow layering. Some suggested techniques are not operational yet

Ecological Modelling, 2008

CoupModel Markov chain Monte Carlo simulation Process-based model Uncertainty estimate a

Biogeochemistry, 2008

A simulation study based on recent regional climate scenarios for Sweden investigated possible ch... more A simulation study based on recent regional climate scenarios for Sweden investigated possible changes in carbon (C) dynamics and net ecosystem exchange (NEE) of Swedish Norway spruce forest ecosystems. Four sites, representative of well-drained soils in four regions, were included. Stand development was simulated for a 100-year rotation period using a coupled model describing abiotic and biotic processes in the soil-plant-atmosphere system. Two IPCC climate change scenarios, corresponding to a mean annual temperature increase of about 2°C (A2) or 3°C (B2) from the reference period 1961-1990 to a new period 2061-2090, were considered. Annual maximum snow depth decreased with the increase in air temperature, whereas maximum soil frost depth and mean annual soil temperature showed only small changes, especially for the sites in northern Sweden. Simulations suggested that in the warmer climate, gross primary production (GPP) increased by 24-32% in northern Sweden and by 32-43% in the south. In the north, the increase was related to the combined effect of air and soil temperature extending the growing season, whereas in the south it was mainly governed by increased N availability due to increased soil temperature. NEE increased by about 20% (A2) or 25% (B2) at all sites, more or less solely due to increased accumulation of C in the tree biomass (including harvest residues), since changes in soil C were small compared with the current climate. Both light use efficiency and water use efficiency were improved in the future climate scenarios, despite increases in atmospheric CO 2 not being considered.

Biogeochemistry, 2008

Depending on the balance between sink and source processes for C, drained organic forest soil eco... more Depending on the balance between sink and source processes for C, drained organic forest soil ecosystems can be in balance or act as net sinks or sources of CO 2 to the atmosphere. In order to study the effect of groundwater level and soil temperature on C-flux, the CoupModel was calibrated (climate data, groundwater levels, soil CO 2 flux, net ecosystem fluxes of CO 2 -exchange, sensible heat flux and latent heat flux, forest production etc.) for a drained forest in Sweden. Bayesian calibration techniques were used to elucidate how different parameters and variables were interlinked in C-circulation. The calibrated model reproduced abiotic and biotic variables reasonably well except for root respiration, which was largely underestimated. Bayesian calibration reduced the uncertainties in the model and highlighted the fact that calibrations should be performed with a high number of parameters instead of specific parameter values.

Annals of Glaciology, 2004

Earlier studies have indicated that the soil on groomed ski slopes may be subjected to more prono... more Earlier studies have indicated that the soil on groomed ski slopes may be subjected to more pronounced cooling than the soil below a natural snowpack. We analyzed the thermal impacts of ski-slope preparation in a sub-alpine ski resort in central Switzerland (1100 m a.s.l.) where artificial snow was produced. Physical snow properties and soil temperature measurements were carried out on the ski slope and off-piste during winter 1999/2000. The numerical soil^vegetation^atmosphere transfer model COUP was run for both locations, with a new option to simulate the snowpack development on a groomed ski slope. Snow density, snow hardness and thermal conductivity were significantly higher on the ski slope than in the natural snowpack. However, these differences did not affect the cooling of the soil, since no difference was observed between the ski slope and the natural snow cover. This might be because cold periods were rare and short and thus any snowpack could protect the soil from freezing. The major impact of the ski-slope grooming was a 4 week delay in snowmelt and soil warming at the end of the season. The newly implemented option proved to be a useful strategy for simulating the snowpack of a ski slope. However, snow density was underestimated by the model as it could not account adequately for compaction due to grooming traffic. Our study demonstrates that there is no site-independent answer as to whether a groomed snowpack affects the thermal conditions in the soil.

AMBIO: A Journal of the Human Environment, 2006

Estimates of carbon fluxes and turnover in ecosystems are key elements in the understanding of cl... more Estimates of carbon fluxes and turnover in ecosystems are key elements in the understanding of climate change and in predicting the accumulation of trace elements in the biosphere. In this paper we present estimates of carbon fluxes and turnover times for five terrestrial ecosystems using a modeling approach. Multiple criteria of acceptance were used to parameterize the model, thus incorporating large amounts of multi-faceted empirical data in the simulations in a standardized manner. Mean turnover times of carbon were found to be rather similar between systems with a few exceptions, even though the size of both the pools and the fluxes varied substantially. Depending on the route of the carbon through the ecosystem, turnover times varied from less than one year to more than one hundred, which may be of importance when considering trace element transport and retention. The parameterization method was useful both in the estimation of unknown parameters, and to identify variability in carbon turnover in the selected ecosystems.

Agricultural and Forest Meteorology, 1999

It is a major challenge in modern science to decrease the uncertainty in predictions of global cl... more It is a major challenge in modern science to decrease the uncertainty in predictions of global climate change. One of the largest uncertainties in present-day global climate models resides with the understanding of processes in the soil±vegetation± atmosphere-transfer (SVAT) system. Continuous, long-term data are needed to correctly quantify balances of water, energy and CO 2 in this system and to correctly model them. It is the objective of this paper to demonstrate how a combined system of existing sensor, computer, and network technologies could be set up to provide continuous and reliable long-term SVATprocess data from an agricultural site under almost all weather conditions. A long-term climate-monitoring system within the framework of NOPEX was set up in 1993±1994 at the Marsta Meteorological Observatory (MMO). It is situated in a¯at agricultural area where annual crops are cultivated on a heavy clay soil. It has successfully monitored relevant states and¯uxes in the system, such as atmospheric¯uxes of momentum, heat, water vapour and CO 2 , atmospheric pro®les of wind speed, direction, and temperature, short-and long-wave radiation, soil temperature, soil-water contents, groundwater levels, and rainfall and snow depth. System uptime has been more than 90% for most of its components during the ®rst 5 years of operation.

Irrigation Science, 2007

A drip-irrigation module was developed and included in an ecosystem model and tested on two indep... more A drip-irrigation module was developed and included in an ecosystem model and tested on two independent datasets, spring and autumn, on field-grown tomato. Simulated soil evaporation correlated well with measurements for spring (2.62 mm d−1 compared to 2.60 mm d−1). Changes in soil water content were less well portrayed by the model (spring r 2 = 0.27; autumn r 2 = 0.45). More independent data is needed for

Research for Policy and Practice, 2012

ABSTRACT Near surface climate was observed through temperature profiling from the surface to 2.47... more ABSTRACT Near surface climate was observed through temperature profiling from the surface to 2.47 m height in an urban vegetated park and its surroundings in central Stockholm, Sweden. Measurements were conducted during three summer days by mobile traverses. Air temperature differences between the built-up area and the park were in the range of 0.5–0.8 °C during the day and reached a maximum of 2 °C at sunset. The thermal stratification of the air was mainly stable in the park and unstable in the built-up area. Inverse air temperature profiles in the park were less stable in open than in shady areas, and close to neutral at midday. The most unstable air was found in the north–south orientated canyons in the early afternoon. Possible heat advection from the surroundings, and thus uncoupling between the surface and the air, was identified through temperature gradients pointing at different directions within the 2.47 m profile. Examples at midday indicated that warm air advected as far as 150 m into the park.

Theoretical and Applied Climatology, 2001

We compared two one-dimensional simulation models for heat and water¯uxes in the soil-snow-atmosp... more We compared two one-dimensional simulation models for heat and water¯uxes in the soil-snow-atmosphere system with respect to their mathematical formulations of the surface heat exchange and the snow pack evolution. They were chosen as examples of a simple one-layer snow model and a more detailed multiple-layer snow model (SNTHERM). The snow models were combined with the same one-dimensional model for the heat and water balance of the underlying soil (CoupModel). Data from an arable ®eld in central Sweden (Marsta), covering two years (1997±1999) of soil temperature, snow depth and eddy-correlation measurements were successfully compared with the models. Conditions with a snow pack deeper or shallower than 10 cm and bare soil resulted in similar discrepancies. The simulated net radiation and sensible heat¯ux were in good agreement with that measured during snow-covered periods, except for situations with snowmelt when the downward sensible heat¯ux was overestimated by 10±20 Wm À2 . The results showed that the uncertainties in parameter values were more important than the model formulation and that both models were useful in evaluating the limitations and uncertainties of the measurements.

Journal of Geophysical Research, 2009

Journal of Applied Meteorology, 2004

ABSTRACT The water and heat balances of an arable field and a forest in the boreal zone in Scandi... more ABSTRACT The water and heat balances of an arable field and a forest in the boreal zone in Scandinavia were explored using 3 yr of observations and simulations with two different soil vegetation atmosphere transfer (SVAT) models over a 30-yr period. Results from a detailed mechanistic model [coupled heat and mass transfer model (COUP)] were compared with those obtained with a large-scale type of SVAT model used in the weather prediction model at the European Centre for Medium-Range Weather Forecasts [ECMWF tiled land surface scheme (TESSEL)]. The COUP model simulations agreed well with the observations from a seasonal perspective. The TESSEL model differed significantly from the measurements when standard operational parameter values were used. The introduction of a seasonal variation in leaf-area index values, tuned canopy resistance for forest, and a reduced roughness length over snow-covered open land reduced the discrepancies. Net radiation was 40% higher in the forest when compared with the arable land, based on 30-yr simulations with both models. Furthermore, the forest was a net source of sensible heat flux, whereas the arable land was a net sink. Because of different treatment of winter interception evaporation, forest latent heat flux based on the COUP model considerably exceeded that from the TESSEL model, and suggested that the total annual evaporation was higher from the forest than from arable land. The representation of interception evaporation in winter, as well as seasonal dynamics in vegetation properties are, thus, of considerable importance for adequate simulation of forest and arable land energy fluxes within the boreal zone.

Journal of Applied Meteorology, 2003

The objective of the present study was to assess the performance and recent improvements of the l... more The objective of the present study was to assess the performance and recent improvements of the land surface scheme used operationally in the European Centre for Medium-Range Weather Forecasts (ECMWF) in a Scandinavian boreal forest climate/ecosystem. The previous (the 1999 scheme of P. Viterbo and A. K. Betts) and the new (Tiled ECMWF Surface Scheme for Exchange Processes over Land,

Hydrology and Earth System Sciences, 2009

Ten conceptually different models in predicting discharge from the artificial Chicken Creek catch... more Ten conceptually different models in predicting discharge from the artificial Chicken Creek catchment in North-East Germany were used for this study. Soil texture and topography data were given to the modellers, but discharge data was withheld. We compare the predictions with the measurements from the 6 ha catchment and discuss the conceptualization and parameterization of the models. The predictions vary in a wide range, e.g. with the predicted actual evapotranspiration ranging from 88 to 579 mm/y and the discharge from 19 to 346 mm/y. The predicted components of the hydrological cycle deviated systematically from the observations, which were not known to the modellers. Discharge was mainly predicted as subsurface discharge with little direct runoff. In reality, surface runoff was a major flow component despite the fairly coarse soil texture. The actual evapotranspiration (AET) and the ratio between actual and potential ET was systematically overestimated by nine of the Correspondence to: H. M. Holländer (hartmut.hollaender@tu-cottbus.de) ten models. None of the model simulations came even close to the observed water balance for the entire 3-year study period. The comparison indicates that the personal judgement of the modellers was a major source of the differences between the model results. The most important parameters to be presumed were the soil parameters and the initial soilwater content while plant parameterization had, in this particular case of sparse vegetation, only a minor influence on the results.

The intersection of the developing topic of rating curve and discharge series uncertainty with th... more The intersection of the developing topic of rating curve and discharge series uncertainty with the topic of hydrological change detection (e.g., in response to land cover or climatic change) has not yet been well studied. The work herein explores this intersection, with consideration of a long-term discharge response for a~650-km 2 headwater basin of the Mara River in west Kenya, starting with stream rating and daily gauge height data. A rating model was calibrated using Bayesian methods to quantify uncertainty intervals in model parameters and predictions. There was an unknown balance of random and systemic error in rating data scatter (a scenario not likely unique to this basin), which led to an unknown balance of noise and information in the calibrated statistical error model. This had implications on testing for hydrological change. Overall, indications were that shifts in basin's discharge response were rather subtle over the 44-year period. A null hypothesis for change using flow duration curves (FDCs) from four different 8-year data intervals could be either accepted or rejected over much of the net flow domain depending on different applications of the statistical error model (each with precedence in the literature). The only unambiguous indication of change in FDC comparisons appeared to be a reduction in lowest baseflow in recent years (flows with >98% exceedance probability). We defined a subjective uncertainty interval based on an intermediate balance of random and systematic error in the rating model that suggested a possibility of more prevalent impacts. These results have relevance to management in the Mara basin and to future studies that might establish linkages to historic land use and climatic factors. The concern about uncertain uncertainty intervals (uncertainty 2 ) extends beyond the Mara and is relevant to testing change where non-random rating errors may be important and subtle responses are investigated. example, magnitudes of flows in the mid-flow region were generally less during 1964-1971 than during 1975-1982 for~40% of the total flow regime.

Hydrological Processes, 2000

Manual snow measurements are becoming increasingly expensive at the same time as climate change i... more Manual snow measurements are becoming increasingly expensive at the same time as climate change imposed snow alterations affect runoff and frost patterns; snow observations are included in runoff modelling, making reliable snow observations outmost important. Multiple new and modified ground-based techniques for monitoring snow depth, density, water equivalent (SWE), wetness, and layering have been tested over the last decade justifying a review of such methods. Techniques based on snow mass, electrical properties, attenuation of radioactivity and, other miscellaneous properties are reviewed. The following sensors seem suitable for registration of temporal variations: Ultrasonic (depth) and terrestrial laser scanning (depth), several snow pillows at the same location (SWE), CRREL/NRCS weighing sensor (SWE), Snowpower (depth, density, SWE and wetness), active and passive (cosmic) gamma-ray attenuation (SWE), and adjusted TDRprobes (density and wetness). Ground penetrating radar (GPR) is, depending on design and operation mode, suitable for different purposes; when arrays of antennas are pulled by a snowmobile the technique is suitable for monitoring of spatial variations in depth, density and SWE for dry snow. Techniques are under development which hopefully will improve the accuracy also for wet snow measurements. Frequency modulated continuous wave (FMCW) GPRs seem fit for measurement of snow layering. Some suggested techniques are not operational yet

Ecological Modelling, 2008

CoupModel Markov chain Monte Carlo simulation Process-based model Uncertainty estimate a

Biogeochemistry, 2008

A simulation study based on recent regional climate scenarios for Sweden investigated possible ch... more A simulation study based on recent regional climate scenarios for Sweden investigated possible changes in carbon (C) dynamics and net ecosystem exchange (NEE) of Swedish Norway spruce forest ecosystems. Four sites, representative of well-drained soils in four regions, were included. Stand development was simulated for a 100-year rotation period using a coupled model describing abiotic and biotic processes in the soil-plant-atmosphere system. Two IPCC climate change scenarios, corresponding to a mean annual temperature increase of about 2°C (A2) or 3°C (B2) from the reference period 1961-1990 to a new period 2061-2090, were considered. Annual maximum snow depth decreased with the increase in air temperature, whereas maximum soil frost depth and mean annual soil temperature showed only small changes, especially for the sites in northern Sweden. Simulations suggested that in the warmer climate, gross primary production (GPP) increased by 24-32% in northern Sweden and by 32-43% in the south. In the north, the increase was related to the combined effect of air and soil temperature extending the growing season, whereas in the south it was mainly governed by increased N availability due to increased soil temperature. NEE increased by about 20% (A2) or 25% (B2) at all sites, more or less solely due to increased accumulation of C in the tree biomass (including harvest residues), since changes in soil C were small compared with the current climate. Both light use efficiency and water use efficiency were improved in the future climate scenarios, despite increases in atmospheric CO 2 not being considered.

Biogeochemistry, 2008

Depending on the balance between sink and source processes for C, drained organic forest soil eco... more Depending on the balance between sink and source processes for C, drained organic forest soil ecosystems can be in balance or act as net sinks or sources of CO 2 to the atmosphere. In order to study the effect of groundwater level and soil temperature on C-flux, the CoupModel was calibrated (climate data, groundwater levels, soil CO 2 flux, net ecosystem fluxes of CO 2 -exchange, sensible heat flux and latent heat flux, forest production etc.) for a drained forest in Sweden. Bayesian calibration techniques were used to elucidate how different parameters and variables were interlinked in C-circulation. The calibrated model reproduced abiotic and biotic variables reasonably well except for root respiration, which was largely underestimated. Bayesian calibration reduced the uncertainties in the model and highlighted the fact that calibrations should be performed with a high number of parameters instead of specific parameter values.

Annals of Glaciology, 2004

Earlier studies have indicated that the soil on groomed ski slopes may be subjected to more prono... more Earlier studies have indicated that the soil on groomed ski slopes may be subjected to more pronounced cooling than the soil below a natural snowpack. We analyzed the thermal impacts of ski-slope preparation in a sub-alpine ski resort in central Switzerland (1100 m a.s.l.) where artificial snow was produced. Physical snow properties and soil temperature measurements were carried out on the ski slope and off-piste during winter 1999/2000. The numerical soil^vegetation^atmosphere transfer model COUP was run for both locations, with a new option to simulate the snowpack development on a groomed ski slope. Snow density, snow hardness and thermal conductivity were significantly higher on the ski slope than in the natural snowpack. However, these differences did not affect the cooling of the soil, since no difference was observed between the ski slope and the natural snow cover. This might be because cold periods were rare and short and thus any snowpack could protect the soil from freezing. The major impact of the ski-slope grooming was a 4 week delay in snowmelt and soil warming at the end of the season. The newly implemented option proved to be a useful strategy for simulating the snowpack of a ski slope. However, snow density was underestimated by the model as it could not account adequately for compaction due to grooming traffic. Our study demonstrates that there is no site-independent answer as to whether a groomed snowpack affects the thermal conditions in the soil.

AMBIO: A Journal of the Human Environment, 2006

Estimates of carbon fluxes and turnover in ecosystems are key elements in the understanding of cl... more Estimates of carbon fluxes and turnover in ecosystems are key elements in the understanding of climate change and in predicting the accumulation of trace elements in the biosphere. In this paper we present estimates of carbon fluxes and turnover times for five terrestrial ecosystems using a modeling approach. Multiple criteria of acceptance were used to parameterize the model, thus incorporating large amounts of multi-faceted empirical data in the simulations in a standardized manner. Mean turnover times of carbon were found to be rather similar between systems with a few exceptions, even though the size of both the pools and the fluxes varied substantially. Depending on the route of the carbon through the ecosystem, turnover times varied from less than one year to more than one hundred, which may be of importance when considering trace element transport and retention. The parameterization method was useful both in the estimation of unknown parameters, and to identify variability in carbon turnover in the selected ecosystems.

Agricultural and Forest Meteorology, 1999

It is a major challenge in modern science to decrease the uncertainty in predictions of global cl... more It is a major challenge in modern science to decrease the uncertainty in predictions of global climate change. One of the largest uncertainties in present-day global climate models resides with the understanding of processes in the soil±vegetation± atmosphere-transfer (SVAT) system. Continuous, long-term data are needed to correctly quantify balances of water, energy and CO 2 in this system and to correctly model them. It is the objective of this paper to demonstrate how a combined system of existing sensor, computer, and network technologies could be set up to provide continuous and reliable long-term SVATprocess data from an agricultural site under almost all weather conditions. A long-term climate-monitoring system within the framework of NOPEX was set up in 1993±1994 at the Marsta Meteorological Observatory (MMO). It is situated in a¯at agricultural area where annual crops are cultivated on a heavy clay soil. It has successfully monitored relevant states and¯uxes in the system, such as atmospheric¯uxes of momentum, heat, water vapour and CO 2 , atmospheric pro®les of wind speed, direction, and temperature, short-and long-wave radiation, soil temperature, soil-water contents, groundwater levels, and rainfall and snow depth. System uptime has been more than 90% for most of its components during the ®rst 5 years of operation.

Irrigation Science, 2007

A drip-irrigation module was developed and included in an ecosystem model and tested on two indep... more A drip-irrigation module was developed and included in an ecosystem model and tested on two independent datasets, spring and autumn, on field-grown tomato. Simulated soil evaporation correlated well with measurements for spring (2.62 mm d−1 compared to 2.60 mm d−1). Changes in soil water content were less well portrayed by the model (spring r 2 = 0.27; autumn r 2 = 0.45). More independent data is needed for