Climatological measurements, including carbon dioxide flux density, were made from April to September in 1994 and from April to November in 1996 at a fen wetland near Thompson, Manitoba, Canada, as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS). For both years, the study period was warmer and drier than the 24‐year climate normals. The period of CO 2 uptake was similar for both years, reaching maximum measured assimilation rates of −0.55 mg m −2 s −1 in midsummer. However, warmer air temperatures and an earlier snowmelt in the spring of 1994, which led to an earlier thaw for the fen surface, and warmer and drier conditions in the fall of 1994 promoted CO 2 production at times when the vascular vegetation was not photosynthesizing. As a result, in 1994 over the study period of 124 days the fen was a net source of CO 2 ‐carbon to the atmosphere, losing 30.8 g C m −2 ; for the same period in 1996 the fen was a net sink of CO 2 ‐carbon, assimilating −91.6 g C m −2 . Given the immense store of carbon in boreal peatlands and given a growing understanding of the relative importance of the soil carbon pool to net ecosystem exchange and of the sensitivity of this carbon storage to temperature and wetness, this boreal fen's response to earlier spring warming and drier conditions extends our understanding of the impact of climate change on the carbon balance for northern ecosystems.
Abstract. This paper describes in situ meteorological forcing and evaluation data, and bias-corrected reanalysis forcing data, for cold regions modelling at ten sites. The long-term datasets (one maritime, one arctic, three boreal and five mid-latitude alpine) are the reference sites chosen for evaluating models participating in the Earth System Model-Snow Model Intercomparison Project. Periods covered by the in situ data vary between seven and twenty years of hourly meteorological data, with evaluation data (snow depth, snow water equivalent, albedo, soil temperature and surface temperature) available at varying temporal intervals. 30-year (1980–2010) time-series have been extracted from a global gridded surface meteorology dataset (Global Soil Wetness Project Phase 3) for the grid cells containing the reference sites, interpolated to one-hour timesteps and bias corrected. Although applied to all sites, the bias corrections are particularly important for mountain sites that are hundreds of meters higher than the grid elevations; as a result, uncorrected air temperatures are too high and snowfall amounts are too low in comparison with in situ measurements. The discussion considers the importance of data sharing to the identification of errors and how the publication of these datasets contributes to good practice, consistency and reproducibility in Geosciences. Supplementary material provides information on instrumentation, an estimate of the percentages of missing values, and gap-filling methods at each site. It is hoped that these datasets will be used as benchmarks for future model development and that their ease of use and availability will help model developers quantify model uncertainties and reduce model errors. The data are published in the repository PANGAEA and available at: https://doi.org/10.1594/PANGAEA.897575.
This study evaluates key aspects of the snow cover, cloud cover, and radiation budget simulated by the Canadian Regional Climate Model, version 4 (CRCM4), coupled with two versions of the Canadian Land Surface Scheme (CLASS). CRCM4 coupled with CLASS version 2.7 has been used operationally at Ouranos since 2006, while, more recently, CRCM4 has been coupled experimentally with CLASS 3.5, which includes a number of improvements to the representation of snow cover processes. The simulations showed evidence of a systematic cold temperature bias. Evaluation of cloud cover and radiation fluxes with satellite data suggests this bias is related to insufficient cloud radiative forcing from a combination of underestimated cloud cover, excessive cloud albedo, and too low cloud emissivity in the model. This cold bias is reinforced by a positive snow albedo feedback manifest through earlier snow cover onset in the fall and early winter period. Snowalbedowasfoundtobeverysensitivetothetreatmentofalbedorefreshbut insignificantlyinfluencedby the partitioning of solid precipitation in CLASS. This study demonstrates that atmospheric forcing can exert a significant impact on the simulation of snow cover and surface albedo. The results highlight the need to evaluate parameterizations in land surface models designed for climate models in fully coupled mode.
Abstract Partitioning of CO 2 exchange into canopy ( F A ) and soil ( F R ) flux components is essential to improve our understanding of ecosystem processes. The stable isotope C 18 OO can be used for flux partitioning, but this approach depends on the magnitude and consistency of the isotope disequilibrium ( D eq ), i.e., the difference between the isotope compositions of F R ( δ A ) and F A ( δ R ). In this study, high temporal resolution isotopic data were used (1) to test the suitability of existing steady state and nonsteady models to estimate H 2 18 O enrichment in a mixed forest canopy, (2) to investigate the temporal dynamics of δ A using a big‐leaf parameterization, and (3) to quantify the magnitude of the C 18 OO disequilibrium ( D eq ) in a temperate deciduous forest throughout the growing season and to determine the sensitivity of this variable to the CO 2 hydration efficiency ( θ eq ). A departure from steady state conditions was observed even at midday in this study, so the nonsteady state formulation provided better estimates of leaf water isotope composition. The dynamics of δ R was mainly driven by changes in soil water isotope composition, caused by precipitation events. Large D eq values (up to 11‰) were predicted; however, the magnitude of the disequilibrium was variable throughout the season. The magnitude of D eq was also very sensitive to the hydration efficiencies in the canopy. For this temperate forest during most of the growing season, the magnitude of D eq was inversely proportional to θ eq , due to the very negative δ R signal, which is contrary to observations for other ecosystems investigated in previous studies.
Abstract. This paper describes ESM-SnowMIP, an international coordinated modelling effort to evaluate current snow schemes, including snow schemes that are included in Earth system models, in a wide variety of settings against local and global observations. The project aims to identify crucial processes and characteristics that need to be improved in snow models in the context of local- and global-scale modelling. A further objective of ESM-SnowMIP is to better quantify snow-related feedbacks in the Earth system. Although it is not part of the sixth phase of the Coupled Model Intercomparison Project (CMIP6), ESM-SnowMIP is tightly linked to the CMIP6-endorsed Land Surface, Snow and Soil Moisture Model Intercomparison (LS3MIP).
Micrometeorological measurements were made over a northern boreal fen near Thompson, Manitoba, Canada, as part of the Boreal Ecosystem‐Atmosphere Study. The measurement period extended from the start of snowmelt until the early fall, at which time senescence was widespread throughout the fen. Data analysis concentrated on identifying seasonal trends in energy, water, and carbon dioxide fluxes and linking them to observed surface cover changes. Albedos (solar and photosynthetically active radiation (PAR)) showed large decreases over the melt period, reaching seasonal lows at the end of melt. Solar albedo increased in the summer in response to vegetation growth on the fen, while PAR albedo remained constant. Incoming and outgoing longwave flux seasonal trends were similar, so seasonal changes in net radiation were driven by the net solar flux. During the spring thaw, the melting of snow and ground ice was equal to about 28% of the daily total net radiation, while the soil heat flux accounted for about 5%. Bowen ratios at this time were above unity. Mean Bowen ratio decreased to 0.70 during the period between spring thaw and leaf‐out. As the vascular vegetation cover developed, Bowen ratios decreased to seasonal lows of 0.10–0.20 near midsummer and then increased to above unity during senescence. The daily evaporative fraction ( EF ) was highest (≥0.80) during midsummer when the vascular vegetation was in full leaf and actively photosynthesizing, and EF decreased to a mean of 0.55 during senescence. Eddy correlation measurements of carbon dioxide flux showed the fen acting as a net sink for CO 2 only while the vascular vegetation was actively photosynthesizing with a daily mean flux of −0.81 g CO 2 ‐C m −2 d −1 (standard error = 0.16). Before leafing and during senescence the fen was a net source of CO 2 . Integrated over the study period of 124 days, the fen experienced a net loss of 30.4 g CO 2 m −2 to the atmosphere.
Abstract. This paper describes in situ meteorological forcing and evaluation data, and bias-corrected reanalysis forcing data, for cold regions' modelling at 10 sites. The long-term datasets (one maritime, one arctic, three boreal, and five mid-latitude alpine) are the reference sites chosen for evaluating models participating in the Earth System Model-Snow Model Intercomparison Project. Periods covered by the in situ data vary between 7 and 20 years of hourly meteorological data, with evaluation data (snow depth, snow water equivalent, albedo, soil temperature, and surface temperature) available at varying temporal intervals. Thirty-year (1980–2010) time series have been extracted from a global gridded surface meteorology dataset (Global Soil Wetness Project Phase 3) for the grid cells containing the reference sites, interpolated to 1 h time steps and bias-corrected. Although the correction was applied to all sites, it was most important for mountain sites hundreds of metres higher than the grid elevations and for which uncorrected air temperatures were too high and snowfall amounts too low. The discussion considers the importance of data sharing to the identification of errors and how the publication of these datasets contributes to good practice, consistency, and reproducibility in geosciences. The Supplement provides information on instrumentation, an estimate of the percentages of missing values, and gap-filling methods at each site. It is hoped that these datasets will be used as benchmarks for future model development and that their ease of use and availability will help model developers quantify model uncertainties and reduce model errors. The data are published in the repository PANGAEA and are available at https://doi.pangaea.de/10.1594/PANGAEA.897575.
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