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1

Monograph available for loan

The surface climates of Canada (1997)

Bailey, William G. [Hrsg.] ; Oke, Timothy R. [Hrsg.] ; Rouse, Wayne R. [Hrsg.]

Montreal [u.a.] : McGill-Queen's Univ. Press

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Call number: PIK N 456-16-90138

Type of Medium: Monograph available for loan

Pages: XXV, 369 S. , Ill., graph. Darst., Kt.

ISBN: 0773509283 , 0773516727

Series Statement: Canadian Association of Geographers series in Canadian geography

URL: Inhaltsverzeichnis

Location: A 18 - must be ordered

Branch Library: PIK Library

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Modelling the interannual variability of net ecosystem CO2 exchange at a subarctic sedge fen (2001)

Griffis, Timothy J. ; Rouse, Wayne R.

Oxford, UK : Blackwell Science Ltd

Global change biology 7 (2001), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: This paper presents an empirical model of net ecosystem CO2 exchange (NEE) developed for a subarctic fen near Churchill, Manitoba. The model with observed data helps explain the interannual variability in growing season NEE. Five years of tower-flux data are used to test and examine the seasonal behaviour of the model simulations. Processes controlling the observed interannual variability of CO2 exchange at the fen are examined by exploring the sensitivity of the model to changes in air temperature, precipitation and leaf area index. Results indicate that the sensitivity of NEE to changing environmental controls is complex and varies interannually depending on the initial conditions of the wetland. Changes in air temperature and the timing of precipitation events have a strong influence on NEE, which is largely manifest in gross ecosystem photosynthesis (GEP). Climate change scenarios indicate that warmer air temperatures will increase carbon acquisition during wet years but may act to reduce wetland carbon storage in years that experience a large water deficit early in the growing season. Model simulations for this subarctic sedge fen indicate that carbon acquisition is greatest during wet and warm conditions. This suggests therefore that carbon accumulation was greatest at this subarctic fen during its early developmental stages when hydroclimatic conditions were relatively wet and warm at approximately 2500 years before present.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1354-1013.2001.00403.x

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3

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The energy and water balance of high-latitude wetlands: controls and extrapolation (2000)

Rouse, Wayne R.

Oxford, UK : Blackwell Publishing Ltd

Global change biology 6 (2000), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: This paper examines, with examples, controls on the energy and water balance of northern wetlands. Most wetlands have organic soils and are thus peatlands. High-latitude wetlands are underlain by ice-rich permafrost, which helps maintain wetland systems and also imparts special characteristics to their energy and water balances. In North America, components of the radiation balance decrease linearly poleward, whereas the poleward rate of decrease of temperature and precipitation lessens. During the four-month summer of a high subarctic wetland, net radiation is large and the latent heat flux dominates the energy cycle. The ground heat flux is substantial, especially in early summer, when the ice-rich ground is rapidly thawing. Winter begins in October and heat loss from the ground approximately balances negative net radiation. The summer energy and water balance differs among terrain units. Large shallow lakes exhibit larger net radiation and potential evaporation rates than surrounding wetland surfaces which, in turn, exhibit substantially larger magnitudes than dryland terrain. There is a variable withdrawal rate of soil moisture depending on soil types and plant rooting characteristics, which influences the actual evaporation from the surface. Synoptic weather systems play a major role in day-to-day energy and water responses to climate forcing. Long-term modelling of the water balance of a wetland shows year-to-year persistence in climatic patterns. Although net radiation, temperature and precipitation all influence the magnitudes of water deficit, the precipitation inputs are of paramount importance. Our ability to fully understand, model and extrapolate, in space and time, the major controls on the surface climate of wetlands, is evaluated. Spatial extrapolation is seen to be more readily achieved than temporal extrapolation.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2486.2000.06013.x

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Land–atmosphere energy exchange in Arctic tundra and boreal forest: available data and feedbacks to climate (2000)

Eugster, Werner ; Rouse, Wayne R ; Pielke Sr, Roger A. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Global change biology 6 (2000), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: This paper summarizes and analyses available data on the surface energy balance of Arctic tundra and boreal forest. The complex interactions between ecosystems and their surface energy balance are also examined, including climatically induced shifts in ecosystem type that might amplify or reduce the effects of potential climatic change.High latitudes are characterized by large annual changes in solar input. Albedo decreases strongly from winter, when the surface is snow-covered, to summer, especially in nonforested regions such as Arctic tundra and boreal wetlands. Evapotranspiration (QE) of high-latitude ecosystems is less than from a freely evaporating surface and decreases late in the season, when soil moisture declines, indicating stomatal control over QE, particularly in evergreen forests. Evergreen conifer forests have a canopy conductance half that of deciduous forests and consequently lower QE and higher sensible heat flux (QH). There is a broad overlap in energy partitioning between Arctic and boreal ecosystems, although Arctic ecosystems and light taiga generally have higher ground heat flux because there is less leaf and stem area to shade the ground surface, and the thermal gradient from the surface to permafrost is steeper.Permafrost creates a strong heat sink in summer that reduces surface temperature and therefore heat flux to the atmosphere. Loss of permafrost would therefore amplify climatic warming. If warming caused an increase in productivity and leaf area, or fire caused a shift from evergreen to deciduous forest, this would increase QE and reduce QH. Potential future shifts in vegetation would have varying climate feedbacks, with largest effects caused by shifts from boreal conifer to shrubland or deciduous forest (or vice versa) and from Arctic coastal to wet tundra. An increase of logging activity in the boreal forests appears to reduce QE by roughly 50% with little change in QH, while the ground heat flux is strongly enhanced.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2486.2000.06015.x

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Scaling net ecosystem CO2 exchange from the community to landscape-level at a subarctic fen (2000)

Griffis, Timothy J. ; Rouse, Wayne R. ; Waddington, J. M.

Oxford, UK : Blackwell Science Ltd

Global change biology 6 (2000), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: Landscape- and community-level CO2 measurements were made at a subarctic sedge fen near Churchill Manitoba during the 1997 growing season. Climatic conditions were warmer and drier than the 30-y normal. Landscape-scale micrometeorological measurements indicated that the wetland gained 49 g CO2 m−2 during the growing season. Chamber-scale measurements from the main vegetation community types showed that small hummocks (Carex spp. sites) dominated the CO2 exchange, yielding an effective scaling factor of 70%. Scaled parameters of two algorithms describing photosynthesis and respiration for each community type show strong similarity to those derived at the landscape level. Scaling photosynthesis, respiration, and net ecosystem CO2 exchange from the community to landscape-level over the season is within the maximum probable error of each methodological approach and helps substantiate the 1997 CO2 budget. We explore the equilibrium response of net ecosystem CO2 exchange of this fen to climatic change by examining the feedback of water table position on vegetation distribution and nitrogen availability. Based on the effective scaling factors computed for each community type, we hypothesize that a small decrease in mean water table position could nearly triple the net uptake of CO2 at this wetland.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2486.2000.00330.x

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6

Electronic Resource

Modelling evaporation from wetland tundra (1994)

Wessel, David A. ; Rouse, Wayne R.

Springer

Boundary layer meteorology 68 (1994), S. 109-130

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ISSN: 1573-1472

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract Evapotranspiration is a major component of both the energy and water balances of wetland tundra environments during the thaw season. Reliable estimates of evapotranspiration are required in the analysis of climatological and hydrological processes occurring within a wetland and in interfacing the surface climate with atmospheric processes. Where direct measurements are unavailable, models designed to accurately predict evapotranspiration for a particular wetland are used. This paper evaluates the performance, sensitivity and limitations of three physically-based, one-dimensional models in the simulation of evaporation from a wetland sedge tundra in the Hudson Bay Lowland near Churchill, Manitoba. The surface of the study site consists of near-saturated peat soil with a sparse sedge canopy and a constantly varying coverage of standing water. Measured evaporation used the Bowen ratio energy balance approach, to which the model results were compared. The comparisons were conducted with hourly and daily simulations. The three models are the Penman-Monteith model, the Shuttleworth-Wallace sparse canopy model and a modified Penman-Monteith model which is weighted for surface area of the evaporation sources. Results from the study suggest that the weighted Penman-Monteith model has the highest potential for use as a predictive tool. In all three cases, the importance of accurately measuring the surface area of each evaporation source is recognized. The difficulty in determining a representative surface resistance for each source and the associated problems in modelling without it are discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00712666

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7

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Impacts of summer warming on the energy and water balance of wetland tundra (1992)

Rouse, Wayne R. ; Carlson, Derek W. ; Weick, E. J.

Springer

Climatic change 22 (1992), S. 305-326

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ISSN: 1573-1480

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract Measurements, made at a high subarctic, maritime, wetland tundra site, are presented for three different growing seasons. These are divided into hot-dry, normal-dry and normal-wet years and the behaviour of their surface energy and water balances is examined within the framework of a combination model. For periods of comparable energy availability, evapotranspiration during hot-dry conditions can be larger than during cooler and wetter periods. This results from small stomatal resistance in the sparse canopy of well-rooted sedges, and from the ability of peat soils to supply water under conditions of large atmospheric demand. This demand is expressed in terms of the vapour pressure deficit and it counteracts the large surface resistances which develop during dry periods. In many respects, the energy balance of a subarctic wetland tundra is comparable to observations and models for temperate agricultural and forest lands, in spite of the fact that the soils are organic, the vegetation canopy is sparse and there is continuous permafrost. A dry year promotes deeper thaw depths in the permafrost soils, during the growing season, than does a wet one. This is due to larger ground heat fluxes and larger soil thermal diffusivities. We concluded that maritime, wetland tundra, growing on peat soils, displays feedback mechanisms, which can offset the effects of moisture stress, caused by summer climate warming of a similar magnitude to that simulated by General Circulation Models for a 2 × CO2 scenario.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00142431

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The influence of surface cover and climate on energy partitioning and evaporation in a subarctic wetland (1988)

Lafleur, Peter M. ; Rouse, Wayne R.

Springer

Boundary layer meteorology 44 (1988), S. 327-347

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ISSN: 1573-1472

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract Energy partitioning and evaporation were measured over three wetland surfaces in a subarctic coastal marsh during pre-growing and growing periods. These surfaces included an alder/willow woodland, a sedge marsh and a raised backshore sedge meadow. A combination model analysis was used to assess the relative importance of surface resistance and meteorological conditions on the magnitude of the Bowen ratio, Β, during the growing period. Overall, the three surfaces experienced important site-to-site and seasonal differences in Β and evaporation, Q E. During the non-foliated period, Q E was largest and Β was smallest for the open water marsh, while the dry backshore site experienced the smallest Q E and largest Β. The non-foliated woodland assumed intermediate values of Β and Q E. After the vegetation covers were established, the woodland assumed the smallest Β and largest Q E flux. It was also found that Β at the marsh site increased with the presence of a vegetation cover. Wind direction was always an important factor in determining Q E and Β at all sites. Β was substantially larger and Q E was smaller for onshore winds (i.e., originating from James Bay) than for offshore winds. The combination model analysis showed that canopy resistance at all sites was largest during warm offshore winds, which were associated with large saturation deficits. However, the effect of increased canopy resistance on Β during offshore winds was offset by a large climatological resistance, resulting in small Β values and large Q E. When winds originated from James Bay, canopy resistance was smaller than for offshore winds, but the climatological resistance also was much smaller, resulting in larger Β and small Q E. The results have important implications for changes in land cover and climate on the regional water balance.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00123020

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Electronic Resource

A Water Balance Model for a Subarctic Sedge Fen and its Application to Climatic Change (1998)

Rouse, Wayne R.

Springer

Climatic change 38 (1998), S. 207-234

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ISSN: 1573-1480

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract A model to calculate the water balance of a hummocky sedge fen in the northern Hudson Bay Lowland is presented. The model develops the potential latent heat flux (evaporation) as a function of net radiation and atmospheric temperature. It is about equally sensitive to a 2% change in net radiation and a 1°C change in temperature. The modelled potential evaporation agrees well with the Priestley–Taylor formulation of evaporation under conditions of a non-limiting water supply. The actual evaporative heat flux is modelled by expressing actual/potential evaporation as a function of potential accumulated water deficit. Model evaporation agrees well with energy balance calculations using 7 years of measured data including wet and dry extremes. Water deficit is defined as the depth of water below reservoir capacity. Modelled water table changes concur with measurements taken over a 4 year period. When net radiation, temperature and precipitation measurements are available the water balance can be projected to longer time periods. Over a 30 year interval (1965–1994) the water balance of the sedge fen showed the following. During the growing season, there was an increase in precipitation, no change in temperature and a decrease in net radiation, evapotranspiration and water deficit. There was also a decrease in winter snow depths. The fen was brought back to reservoir capacity during final snowmelt every year but one. Summer rainfall was the most important single factor affecting the water balance and the ratio actual/potential evaporation emerged as a linear function of rainfall amount. A 2 × CO2 climate warming scenario with an annual temperature increase of 4°C and no precipitation change indicates lesser snow amounts and a shorter snow cover period. A greater summer water deficit, triggered mainly by greater evaporation during the month of May, is partially alleviated by lesser evaporation magnitudes in July. The greater water deficit would be counterbalanced by a 23% increase in summer rainfall. On average, the fen's water reservoir would still be recharged after winter snowmelt but the ground would remain at reservoir capacity for a shorter time. The warming scenario with a 10% decline in summer rainfall would create a large increase in the longevity and severity of the water deficit and this would be particularly evident during drier years. The carbon budget and peat accumulation and breakdown rates are strongly affected by changes in the water balance. Some evidence implies that greater water deficits lead to an increase in net carbon emissions. This implies that the sedge peatland could lose biomass under such conditions. An example is given where increased water deficit results in large decreases in local wetland streamflow.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1005358017894

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