| 1. |
- Arheimer, Berit, et al.
(author)
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Catchment modelling at the global scale using the World-Wide HYPE (WWH)
- 2019
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Conference paper (peer-reviewed)abstract
- Recent advancements in catchment hydrology (such as understanding hydrological processes, accessing new data sources, and refining methods for parameter constraints) make it possible to apply catchment models for ungauged basins over large domains. Here we present a cutting-edge case study applying catchment-modelling techniques at the global scale for the first time. The modelling procedure was challenging but doable and even the first model version show better performance than traditional gridded global models of river flow. We used the open-source code of the HYPE model and applied it for > 130 000 catchments (with an average resolution of 1000 km2), delineated to cover the Earths landmass (except Antarctica). The catchments were characterized using 20 open databases on physiographical variables, to account for spatial and temporal variability of the global freshwater resources, based on exchange with the atmosphere (e.g. precipitation and evapotranspiration) and related budgets in all compartments of the land (e.g. soil, rivers, lakes, glaciers, and floodplains), including water stocks, residence times, interfacial fluxes, and the pathways between various compartments. Global parameter values were estimated using a step-wise approach for groups of parameters regulating specific processes and catchment characteristics in representative gauged catchments. Daily time-series (> 10 years) from 5338 gauges of river flow across the globe were used for model evaluation (half for calibration and half for independent validation), resulting in an average monthly KGE of 0.4. However, the world-wide HYPE (WWH) model shows large variation in model performance, both between geographical domains and between various flow signatures. The model performs best in Eastern USA, Europe, South-East Asia, and Japan, as well as in parts of Russia, Canada, and South America. The model shows overall good potential to capture flow signatures of monthly high flows, spatial variability of high flows, duration of low flows and constancy of daily flow. Nevertheless, there remains large potential for model improvements and we suggest both redoing the calibration and reconsidering parts of the model structure for the next WWH version. The calibration cycle should be repeated a couple of times to find robust values under new fixed parameter conditions. For the next iteration, special focus will be given to precipitation, evapotranspiration, soil storage, and dynamics from hydrological features, such as lakes, reservoirs, glaciers, and floodplains. This first model version clearly indicates challenges in large scale modelling, usefulness of open data and current gaps in processes understanding. Parts of the WWH can be shared with other modellers working at the regional scale to appreciate local knowledge, establish a critical mass of experts and improve the model in a collaborative manner. Setting up a global catchment model has to be a long-term commitment of continuous model refinements to achieve successful and truly useful results.
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| 2. |
- Arheimer, Berit, et al.
(author)
-
Global catchment modelling usingWorld-Wide HYPE (WWH), open data, and stepwise parameter estimation
- 2020
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In: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 24:2, s. 535-559
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Journal article (peer-reviewed)abstract
- Recent advancements in catchment hydrology (such as understanding catchment similarity, accessing new data sources, and refining methods for parameter constraints) make it possible to apply catchment models for ungauged basins over large domains. Here we present a cutting-edge case study applying catchment-modelling techniques with evaluation against river flow at the global scale for the first time. The modelling procedure was challenging but doable, and even the first model version showed better performance than traditional gridded global models of river flow. We used the open-source code of the HYPE model and applied it for > 130 000 catchments (with an average resolution of 1000 km2), delineated to cover the Earth’s landmass (except Antarctica). The catchments were characterized using 20 open databases on physiographical variables, to account for spatial and temporal variability of the global freshwater resources, based on exchange with the atmosphere (e.g. precipitation and evapotranspiration) and related budgets in all compartments of the land (e.g. soil, rivers, lakes, glaciers, and floodplains), including water stocks, residence times, and the pathways between various compartments. Global parameter values were estimated using a stepwise approach for groups of parameters regulating specific processes and catchment characteristics in representative gauged catchments. Daily and monthly time series (> 10 years) from 5338 gauges of river flow across the globe were used for model evaluation (half for calibration and half for independent validation), resulting in a median monthly KGE of 0.4. However, the World-Wide HYPE (WWH) model shows large variation in model performance, both between geographical domains and between various flow signatures. The model performs best (KGE> 0:6) in the eastern USA, Europe, South-East Asia, and Japan, as well as in parts of Russia, Canada, and South America. The model shows overall good potential to capture flow signatures of monthly high flows, spatial variability of high flows, duration of low flows, and constancy of daily flow. Nevertheless, there remains large potential for model improvements, and we suggest both redoing the parameter estimation and reconsidering parts of the model structure for the next WWH version. This first model version clearly indicates challenges in large-scale modelling, usefulness of open data, and current gaps in process understanding. However, we also found that catchment modelling techniques can contribute to advance global hydrological predictions. Setting up a global catchment model has to be a longterm commitment as it demands many iterations; this paper shows a first version, which will be subjected to continuous model refinements in the future. WWH is currently shared with regional/local modellers to appreciate local knowledge.
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| 3. |
- Crochemore, Louise, et al.
(author)
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Lessons learnt from checking the quality of openly accessible river flow data worldwide
- 2019
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In: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435.
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Journal article (peer-reviewed)abstract
- Advances in open data science serve large-scale model developments and, subsequently, hydroclimate services. Local river flow observations are key in hydrology but data sharing remains limited due to unclear quality, or to political, economic or infrastructure reasons. This paper provides methods for quality checking openly accessible river-flow time series. Availability, outliers, homogeneity and trends were assessed in 21 586 time series from 13 data providers worldwide. We found a decrease in data availability since the 1980s, scarce open information in southern Asia, the Middle East and North and Central Africa, and significant river-flow trends in Africa, Australia, southwest Europe and Southeast Asia. We distinguish numerical outliers from high-flow peaks, and to integrate all investigated quality characteristics in a composite indicator. We stress the need to maintain existing gauging networks, and highlight opportunities in extending existing global databases, understanding drivers for trends and inhomogeneity, and in innovative acquisition methods in data-scarce regions.Keywords: open data, river flow, global hydrology, quality control, time series
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| 4. |
- Hasan, Abdulghani
(author)
-
Dynamic modeling of urban hydrology in a geographic information system-setting with TFM-DYN
- 2024
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In: Geographical Information Science : Case Studies in Earth and Environmental Monitoring. - 9780443136054 ; , s. 315-336
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Book chapter (peer-reviewed)abstract
- The TFM-DYN model represents a significant advancement from static flow accumulation estimations into dynamic hydrological modeling (Nilsson et al., 2021). It incorporates variable precipitation in time and space as input together with high-resolution topography and includes functions for friction and infiltration to produce results such as water depths, flow velocity, inundated areas, flow pathways, and drainage areas for each point in the landscape. All water volumes in the simulation, whether moved, infiltrated, or input into the stormwater network, are recorded per time step and can be visualized in a geographic information system (GIS). All output data are saved in GIS layers, which can be visualized and managed in standard GIS software for further analyses. The versatility of this model extends beyond urban hydrological issues. Its application spans over a wide range of hydrological analyses in diverse landscapes.
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| 5. |
- Hasan, Abdulghani
(author)
-
Flood Modelling Tool : an integrated GIS and hydrological modelling tool for planning nature-based solutions in the urban environment
- 2024
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Reports (other academic/artistic)abstract
- The risk of pluvial flooding is going to increase as climate change causes an increase in intense precipitation along with urbanisation leading to an increase in impermeable surfaces. In the last decade, cities such as Malmö and Copenhagen have already experienced severe pluvial flooding that has caused extensive damage. Adapting to climate change by creating flood resilient urban areas is therefore important and blue-green infrastructure (BGI) may be one measure to accomplish this.A hydrological model called TFM-DYN has been used to investigate whether BGI can aid the mitigation of pluvial flooding. TFM-DYN can also assist in selecting the best locations of BGIs. The problem of modeling urban floods using distributed high resolution hydrological models while considering the hydrological process in the upstream area is difficult due to the limited current computation capacity. However, coupling a distributed hydrological model (TFM-DYN) with an other semi distributed models (HYPE) is crucial to enable simulate, predict and map floods with high-resolution for an urban area while considering its catchment area. With the using of the new suggested coupled hydrological model, it is possible to connect and use the output results from HYPE model as an input to a distributed model (TFM-DYN). The interaction between HYPE and TFM-DYN will consider the hydrologic process occurred outside the model boundary of the interested urban area. The coupling of the two models will help initiating the model with real water depth data that may lead to more realistic simulation. The procedure of input data manipulation using the two model interactions is explained in details.The model is tested on a selected urban area to dynamically simulate the changes in the water depth with time using high resolution gridded data. The new coupled model can be of a great tool for wide range of user and stakeholders as an example to municipalities, water experts, insurance companies and to all other interested water organizations who have access to regional catchment models and in need for a high-resolution, flood simulation and mapping model.
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| 6. |
- Hasan, Abdulghani, et al.
(author)
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On generating digital elevation models from liDAR data – resolution versus accuracy and topographic wetness index indices in northern peatlands
- 2012
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In: Geodesy and Cartography. - : Vilnius Gediminas Technical University. - 2029-6991 .- 2029-7009. ; 38:2, s. 57-69
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Journal article (peer-reviewed)abstract
- Abstract Global change and GHG emission modelling are dependent on accurate wetness estimations for predictions of e.g. methane emissions. This study aims to quantify how the slope, drainage area and the TWI vary with the resolution of DEMs for a flat peatland area. Six DEMs with spatial resolutions from 0.5 to 90 m were interpolated with four different search radiuses. The relationship between accuracy of the DEM and the slope was tested. The LiDAR elevation data was divided into two data sets. The number of data points facilitated an evaluation dataset with data points not more than 10 mm away from the cell centre points in the interpolation dataset. The DEM was evaluated using a quantile-quantile test and the normalized median absolute deviation. It showed independence of the resolution when using the same search radius. The accuracy of the estimated elevation for different slopes was tested using the 0.5 meter DEM and it showed a higher deviation from evaluation data for steep areas. The slope estimations between resolutions showed differences with values that exceeded 50%. Drainage areas were tested for three resolutions, with coinciding evaluation points. The model ability to generate drainage area at each resolution was tested by pair wise comparison of three data subsets and showed differences of more than 50% in 25% of the evaluated points. The results show that consideration of DEM resolution is a necessity for the use of slope, drainage area and TWI data in large scale modelling. Global change and GHG emission modelling are dependent on accurate wetness estimations for predictions of e.g. methane emissions. This study aims to quantify how the slope, drainage area and the TWI vary with the resolution of DEMs for a flat peatland area. Six DEMs with spatial resolutions from 0.5 to 90 m were interpolated with four different search radiuses. The relationship between accuracy of the DEM and the slope was tested. The LiDAR elevation data was divided into two data sets. The number of data points facilitated an evaluation dataset with data points not more than 10 mm away from the cell centre points in the interpolation dataset. The DEM was evaluated using a quantile-quantile test and the normalized median absolute deviation. It showed independence of the resolution when using the same search radius. The accuracy of the estimated elevation for different slopes was tested using the 0.5 meter DEM and it showed a higher deviation from evaluation data for steep areas. The slope estimations between resolutions showed differences with values that exceeded 50%. Drainage areas were tested for three resolutions, with coinciding evaluation points. The model ability to generate drainage area at each resolution was tested by pair wise comparison of three data subsets and showed differences of more than 50% in 25% of the evaluated points. The results show that consideration of DEM resolution is a necessity for the use of slope, drainage area and TWI data in large scale modelling.
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| 7. |
- Hasan, Abdulghani
(author)
-
Spatially Distributed Hydrological Modelling : Wetness Derived from Digital Elevation Models to Estimate Peatland Carbon
- 2012
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Doctoral thesis (other academic/artistic)abstract
- To study the hydrology of peatlands and explore wetness distribution is difficultmainly due to the complexity of the surface of peatlands, and also due to the presence of permafrost underlain peatlands in the arctic regions. I have chosen the area called Stordalen mire in the arctic region in northern Sweden for my study.In this thesis, I aimed to study spatially distributed hydrological modelling in general, focusing mainly on evaluation and developing tools that can be used to improve wetness estimation using Digital Elevation Models (DEMs). The estimated wetness can be used as an input for peatland carbon models.DEMs with different resolutions are created using high resolution LiDAR data.Different search radiuses are used in the interpolations. The accuracy of the generated DEMs is studied to select the most accurate DEM for each selected resolution. The search radius, but not the cell size, significantly influences the accuracy of a DEM, and the accuracy is generally higher the shorter the interpolation search radius. DEM resolution versus topographic wetness index variables (i.e. slope and drainage area) is studied. Slope values become lower and drainage area values become higher when the resolution decreases. Further, a study of DEM accuracy related to different slopes is also carried out and shows that the errors in elevation are greater when the terrain is steep than when it is flat.A new triangular form-based multiple flow distribution and flow accumulationalgorithm (TFM) was created in this study. We have estimated flow distribution by using our new TFM algorithm. With this TFM algorithm, it becomes possible to deal with artefacts that normally interrupt flow distribution, like flat areas, sinks and manmade structures. This will help to overcome the complexity of peatland hydrology.The results of comparing our new algorithm with other well-known algorithms used in most GIS programs show that the TFM algorithm produces more realistic results than other algorithms. Testing shows the capability of the new TFM algorithm to distribute the flow in different terrain types, flat areas and sinks, and makes it suitable for simulating real flow distribution over any surface/terrain. Topographic wetness index (TWI) was estimated for the study area using our newflow distribution and flow accumulation algorithm TFM. Estimating TWI valuesdepending only on DEMs is a very cost-effective method that can be used to estimate wetness data required for the modelling of peatlands. A permafrost model was created to demonstrate the possibility of using an analytically based approach with semiempirical equations to estimate the maximum thawing depth (active layer thickness) above permafrost. Field work using water level sensors was carried out to measure the temporal fluctuation of water surface. The field work water level measurements led to better understanding of flow regime in the peatlands, especially when a seasonally frozen layer or permafrost lies under it. The field work also helped to confirm that estimated wetness using the proposed flow routing algorithm on digital elevation model can be used to distribute wetness to all cells in a DEM.
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| 8. |
- Neves, José Lourenço, 1981, et al.
(author)
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Flood risk assessment under population growth and urban land use change in Matola, Mozambique
- 2023
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In: African Geographical Review. - : Informa UK Limited. - 1937-6812 .- 2163-2642. ; 42:5, s. 539-559
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Journal article (peer-reviewed)abstract
- Matola, a major Mozambican city, has witnessed flooding, mainly caused by rainfall. The study aims to produce flood-hazard and flood-risk maps for Matola using the hydrological model TFM-DYN. For 2000, 2020, and 2040, the modeled extent of medium-risk area is 50.6 km2 (13.7%), 44.8 km2 (12.2%), and 39.0 km2 (10.6%) and of high-risk area is 43.3 km2 (11.8%), 31.8 km2 (8.6%), and 28.9 km2 (7.8%), respectively. In 2000, 61,978.4 inhabitants were exposed to medium-risk and 53,036.8 to high-risk. In 2020, 130,628.3 inhabitants were vulnerable to medium-risk and 92,722.8 to high-risk. By 2040, 203,999.8 inhabitants will face medium-risk and 151,169.1 high-flood-risk
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| 9. |
- Nilsson, Hampus, et al.
(author)
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Dynamic spatio‐temporal flow modeling with raster DEMs
- 2022
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In: Transactions in GIS. - : Wiley. - 1467-9671 .- 1361-1682. ; 26:3, s. 1572-1588
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Journal article (peer-reviewed)abstract
- A user-friendly high-resolution intermediate complexity dynamic and spatially distributed flow model is crucial in urban flood modeling. Planners and consultants need to improve the accuracy of floods and estimation of risks. A new flow model will serve as a rapid tool to improve identification of these. This article provides a detailed explanation of a model based on a multiple flow algorithm. Model testing was performed on selected urban and rural areas. Additionally, a sensitivity analysis is conducted to analyze functionality. The model includes basic hydrological processes and is therefore less complex than fully physical models. The data needed to set up and run the new model include spatially and temporally distributed basic geometric and hydrologic variables (i.e., digital elevation model, precipitation, infiltration, and surface roughness). The model is implemented using open-source coding and can easily be applied to any selected area. Outputs are water volumes, depths, and velocities at different modeling times. Using GIS, results can be visualized and utilized for further analyses. The test, applied in urban as well as rural areas, demonstrates its user-friendliness, and that the estimated distributed water depths and water velocity at any time step can be saved and visualized.
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| 10. |
- Persson, Andreas, et al.
(author)
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Modelling flow routing in permafrost landscapes with TWI : an evaluation against site-specific wetness measurements
- 2012
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In: Transactions in GIS. - : Wiley. - 1467-9671 .- 1361-1682. ; 16:5, s. 701-713
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Journal article (peer-reviewed)abstract
- In northern peatlands the thawing of permafrost increasing the active layer depth and changing the hydrology may lead to feedbacks in the climate system through changes in the biogeochemistry of carbon. We are examining this association on the Stordalen peatland complex in subarctic Sweden by analyzing a DEM derived from LiDAR-data and the calculated TWI. The DEM, with a spatial resolution of 1 m, and the TWI are evaluated against two seasons of water level measurements from 30 sites in the peatland. The TWI is calculated with a form-based flow routing algorithm which produces a natural flow routing pattern. In permafrost wetlands the topography is the major driver and is very important even though its magnitude is low. Site-specific wetness (SSW) measurements from the sites were compared with the different peatland types that occur in the study area, i.e. fen, internal fen and palsa. The results showed a strong correlation between the TWI and the palsa. The TWI was better at describing general patterns than site-specific hydrology. The evaluation of spatial patterns of TWI against SSW reveal the resolution required to develop the technique to be useful for climate change studies.
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| 11. |
- Pilesjö, Petter, et al.
(author)
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A triangular form-based multiple flow algorithm to estimate overland flow distribution and accumulation on a digital elevation model
- 2014
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In: Transactions in GIS. - : Wiley. - 1467-9671 .- 1361-1682. ; 18:1, s. 108-124
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Journal article (peer-reviewed)abstract
- In this study, we present a newly developed method for the estimation of surface flow paths on a digital elevation model (DEM). The objective is to use a form-based algorithm, analyzing flow over single cells by dividing them into eight triangular facets and to estimate the surface flow paths on a raster DEM. For each cell on a gridded DEM, the triangular form-based multiple flow algorithm (TFM) was used to distribute flow to one or more of the eight neighbor cells, which determined the flow paths over the DEM. Because each of the eight facets covering a cell has a constant slope and aspect, the estimations of – for example – flow direction and divergence/convergence are more intuitive and less complicated than many traditional raster-based solutions. Experiments were undertaken by estimating the specific catchment area (SCA) over a number of mathematical surfaces, as well as on a real-world DEM. Comparisons were made between the derived SCA by the TFM algorithm with eight other algorithms reported in the literature. The results show that the TFM algorithm produced the closest outcomes to the theoretical values of the SCA compared with other algorithms, derived more consistent outcomes, and was less influenced by surface shapes. The real-world DEM test shows that the TFM was capable of modeling flow distribution without noticeable ‘artefacts’, and its ability to track flow paths makes it an appropriate platform for dynamic surface flow simulation.
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| 12. |
- Vestin, Patrik, et al.
(author)
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Impacts of Clear-Cutting of a Boreal Forest on Carbon Dioxide, Methane and Nitrous Oxide Fluxes
- 2020
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In: Forests. - : MDPI AG. - 1999-4907. ; 11:9
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Journal article (peer-reviewed)abstract
- The 2015 Paris Agreement encourages stakeholders to implement sustainable forest management policies to mitigate anthropogenic emissions of greenhouse gases (GHG). The net effects of forest management on the climate and the environment are, however, still not completely understood, partially as a result of a lack of long-term measurements of GHG fluxes in managed forests. During the period 2010-2013, we simultaneously measured carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes using the flux-gradient technique at two clear-cut plots of different degrees of wetness, located in central Sweden. The measurements started approx. one year after clear-cutting, directly following soil scarification and planting. The study focused on robust inter-plot comparisons, spatial and temporal dynamics of GHG fluxes, and the determination of the global warming potential of a clear-cut boreal forest. The clear-cutting resulted in significant emissions of GHGs at both the wet and the dry plot. The degree of wetness determined, directly or indirectly, the relative contribution of each GHG to the total budgets. Faster establishment of vegetation on the wet plot reduced total emissions of CO2 as compared to the dry plot but this was partially offset by higher CH4 emissions. Waterlogging following clear-cutting likely caused both plots to switch from sinks to sources of CH4. In addition, there were periods with N2O uptake at the wet plot, although both plots were net sources of N2O on an annual basis. We observed clear diel patters in CO2, CH4 and N2O fluxes during the growing season at both plots, with the exception of CH4 at the dry plot. The total three-year carbon budgets were 4107 gCO(2)-equivalent m(-2) and 5274 gCO(2)-equivalent m(-2) at the wet and the dry plots, respectively. CO2 contributed 91.8% to the total carbon budget at the wet plot and 98.2% at the dry plot. For the only full year with N2O measurements, the total GHG budgets were 1069.9 gCO(2)-eqvivalents m(-2) and 1695.7 gCO(2)-eqvivalents m(-2) at the wet and dry plot, respectively. At the wet plot, CH4 contributed 3.7%, while N2O contributed 7.3%. At the dry plot, CH4 and N2O contributed 1.5% and 7.6%, respectively. Our results emphasize the importance of considering the effects of the three GHGs on the climate for any forest management policy aiming at enhancing the mitigation potential of forests.
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| 13. |
- Vestin, Patrik, et al.
(author)
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Impacts of stump harvesting on carbon dioxide, methane and nitrous oxide fluxes
- 2022
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In: Iforest-Biogeosciences and Forestry. - : Italian Society of Sivilculture and Forest Ecology (SISEF). - 1971-7458. ; 15, s. 148-162
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Journal article (peer-reviewed)abstract
- During 2010-2013, we investigated the effects of stump harvesting on greenide (N2O) with the flux-gradient technique at four experimental plots in a hemiboreal forest in Sweden. All plots were clear-cut and soil scarified and two of the plots were additionally stump harvested. The two clear-cut plots served as control plots. Due to differences in topography, we had one wetter and one drier plot of each treatment. All plots exhibited substantial emissions of GHGs and we noted significant effects of wetness on CO2, CH4 and N2O fluxes within treatments and significant effects of stump harvesting on CO2 and N2O fluxes at the dry plots. The CO2 emissions were lower at the dry stump harvested plot than at the dry control, but when estimated emissions from the removed stumps were added, total CO2 emissions were higher at the stump harvested plot, indicating a small enhancement of soil respiration. In addition, we noted significant emissions of N2O at this plot. At the wet plots, CO2 emissions were higher at the stump harvested plot, also suggesting a treatment effect but differences in wetness and vegetation cover at these plots make this effect more uncertain. At the wet plots, we noted sustained periods (weeks to months) of net N2O uptake. During the year with simultaneous measurements of the abovementioned GHGs, GHG budgets were 1.224??103 and 1.442??103 gm-2 of CO2-equivalents at the wet and dry stump harvested plots, respectively, and 1.070??103 and 1.696??103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. CO2 fluxes dominated GHG budgets at all plots but N2O contributed with 17% at the dry stump harvested plot. For the full period 2010-2013, total carbon (CO2+CH4) budgets were 4.301??103 and 4.114??103 g m-2 of CO2-eqvivalents at the wet and dry stump harvest plots, respectively and 4.107??103 and 5.274??103 gm-2 of CO2-equivalents at the wet and dry control plots, respectively. Our results support recent studies suggesting that stump harvesting does not result in substantial increase in CO2 emissions but uncertainties regarding GHG fluxes (especially N2O) remain and more long-term measurements are needed before robust conclusions can be drawn.
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