The human imprint on land-atmosphere exchange in high latitudes

Human land management contributes to climate change through different pathways: Global net carbon emissions from land use/cover change constitute ~12.5% of total carbon emissions. At the same time, land management modifies biochemical and biophysical properties of the land surface that govern energy and water fluxes between the land surface and the atmosphere. In Norway, large-scale transitions in forest structure due to forest management have been the most widespread land management impact over the past decades, and forest management will continue to shape landscape and forest structure throughout the 21st century. IMPRINT investigated the effects of past and future land use and forest management on biogeophysical processes that govern the exchange of energy and water between the land surface and the atmosphere. The project focussed on three intertwined land surface processes that are particularly sensitive to both climatic change and human interference from land use and forest management: 1) snow accumulation and melt, 2) land energy balance and 3) soil water dynamics. In order to better understand and predict these processes, numerical process models and statistical modelling were combined with the best available satellite and ground measurements. The first part of the project focused on developing improved forcing datasets that facilitate studying and simulating exchange processes between the land surface and the atmosphere: (1) A present-day land use map has been produced that augments the best available national land use information with a detailed representation of forest cover and structure derived from remote sensing and forest inventory data. Taking today’s land use as a starting point, a suite of land use and forest management scenarios for the 21st century have been developed that reflect varying degrees of warming and different levels of harvest intensities. (2) A high-resolution atmospheric forcing dataset has been produced that combines national, gridded meteorological observations with state-of-the-art global atmospheric reanalysis in a physically consistent manner. The dataset has built the basis for developing improved national climate projections for the period 1960-2100 which have been finalized for three regional climate models and three global warming scenarios each. One main goal of the project was to improve process-based and statistical modelling of land surface processes aided by various observational data-sets. The main improvements achieved include: (1) snow simulations have been scrutinized against snow cover observed by satellites as well as against in-situ data at eight Scandinavian ICOS flux tower observation sites, (2) different approaches to estimate forest transpiration have been benchmarked against in-situ measurements, (3) an improved parametric model for estimating downwelling longwave irradiance has been developed, and (4) model-simulated soil moisture patterns have been evaluated with satellite observations. In the final phase of the project, the improved modelling approaches were integrated with the forest management and climate scenarios in order to quantify the effects of past and future land use and forest management on the exchange of energy and water between the land surface and the atmosphere in a changing climate. Results showed, for example, that land-atmosphere exchange is dominated by the climate change signal at the regional scale, however the effects of forest cover and density as shaped by forest management can be considerable at the local scale. A stakeholder workshop was arranged for stakeholders within forestry and agriculture in collaboration with the NFR project EMERALD and the Norwegian Centre for Climate Services. The main goal of the workshop was to identify specific needs for climate information in the agriculture and forestry sectors. Based on the results from the workshop, a web page report aimed at stakeholders was developed (https://arcg.is/1CaWb0).

IMPRINT has generated increased knowledge, improved methods and datasets, and detailed quantitative estimates of the interactions between forest and land management, climate, and surface energy and water fluxes. This provides foundation for making climate-smart forest and land management decisions and for prioritizing forest-based climate adaptation and mitigation measures. The project’s methods and results will through the project partners be built into the national infrastructure, thus providing post-project decision support for policy development and climate change adaptation. The project has established a strong cooperation between the research partners which will be beneficial for developing future projects. Several novel datasets have been generated that have great potential for and are already being utilized in follow-up projects.

Human activity simultaneously impacts on the composition of and the interactions between atmosphere, hydrosphere and biosphere. Anthropogenic greenhouse gas emissions are the main driver of changes in moisture supplied to and energy available at the land surface. At the same time, land use and land management modify biochemical and biophysical vegetation properties that govern energy and water fluxes between the land surface and the atmosphere. In Norway large scale transitions in forest structure are the most widespread land management impact and IMPRINT will investigate how forest management has effected land surface energy and water fluxes over the past ~60 years. This has so far not been quantified. To this end, process-based and empirically-based modelling approaches will be jointly developed and/or refined and benchmarked against remote sensing and ground observations. The project will further develop coherent climate and forest management scenarios in order to provide projections of land-atmosphere fluxes throughout the 21st century under time evolving anthropogenic forcing. IMPRINT will provide an advance over previous (coarse-scale) approaches to quantify these effects in several aspects: (1) the land use scenarios build on national data sources, i.e. statistics, forest inventory information, and vegetation surveys, thus better reflecting the specific cultural history of land utilization in Norway which will shape future land management practices; (2) the simulations are carried out at fine spatial resolution (1 km), thus accounting to a greater extent for spatial heterogeneity in biotic and abiotic factors governing energy and water fluxes; and (3) process descriptions are benchmarked and/or refined aided by local ground observations and remote sensing to test and ensure their specific applicability in the study domain, i.e. Norway.