Permafrost ecosystems entangled with human life in Mongolia- evaluating the impact of land use change in a warming climate

The Permafrost4Life project investigates permafrost and climate in Mongolia with a combination of field measurements, remote sensing and numerical modeling. In particular, the project investigates the complex relationship between permafrost, ecosystems and the traditional herder lifestyle that is of great importance for the Mongolian society. The southern boundary of the Eurasian permafrost extent runs straight across Mongolia, and climate change has already led to a significant reduction of the permafrost area in the last decades. In a first published study, the project team has evaluated air temperature measurements since the 1950s from dozens of meteorological stations throughout Mongolia which clearly show that climate conditions have become much less favourable for permafrost occurrence. While the first part of the project period was dominated by travel restrictions due to the Covid-19 pandemic, there has been extensive joint fieldwork of the Norwegian and Mongolian project teams in the past years, with the project leader Sebastian Westermann spending about six months in Mongolia. In particular, we instrumented field areas in the Henti mountains and around lake Hovsgol with temperature loggers that have continuously measured ground temperatures for different expositions and altitudes, as well as landcover types (dead and intact forests, shrublands, grasslands) and livestock grazing intensities. Furthermore, we characterized important environmental parameters, such vegetation height and structure, as well as winter snow depth. Several more scientific publications have resulted from this work: first, we could show that mean annual ground temperatures feature a variability of more than 8°C within a small valley system, with exposition and forest occurrence the dominant environmental controls, while the temperature was largely independent of the altitude of the measurement site. A second study focussed on the complex effect of grazing by livestock on ground temperatures. While heavy grazing led to much higher temperatures in summer, the winter temperatures were considerably lowered, as the animals trampled the snow and thus strongly reduced the insulation of the ground from the cold air. Grazing can therefore increase or decrease ground temperatures, depending on the intensity at different times of the year. This result is of practical relevance for land management in permafrost areas, as grazing in areas with thawing permafrost could be limited to the winter season, so that ground temperatures are lowered to protect the permafrost. Finally, we investigated the effect of a forest cover on ground temperatures with numerical simulations with the CryoGrid community model developed at the University of Oslo. Our results show that the shading of a forest cover does not directly lower the mean annual ground temperatures, as was assumed in previous studies, but rather influences the soil water content in the summer season. This suggests that permafrost does not necessarily start to thaw when forests are removed due to insect outbreaks, wildfires or logging. This important finding is supported by field measurements at a site with destroyed forest which clearly show that the mean annual ground temperatures are not increased compared to an intact forest at similar altitudes and expositions. The Permafrost4Life project has established a tight and trustful collaboration between Norwegian and Mongolian researchers which we will continue after the end of the project. For the dissemination of project results, Permafrost4Life is in the unique situation that our Mongolian project partners maintain strong connections to the local people affected by climate change. Several of the scientists have grown up in active herder families on the Mongolian countryside, giving them an intimate understanding of the challenges of this lifestyle. This makes it easy to communicate with local people and authorities, so that they are able to disseminate project results at eye level, and not through the potentially biased perspective of a Western scientist.

Central Asia is one of the very few areas in the world were ecosystems and human life are heavily entangled with the Cryosphere, with a continental climate favoring the occurrence of permafrost. About one third of Mongolian municipalities are located in permafrost areas, and the density of livestock is by far highest in permafrost-dominated regions. This is due to more abundant water sources, thus sustaining a traditional, semi-nomadic lifestyle for about 30% of the population of Mongolia, while also supplying food to the growing urban centers. Permafrost provides water from melting ground ice in the dry summer season, or by preventing rainwater from infiltrating into deeper layers, thus leaving it available for plant growth. Increases in temperature have led to ongoing and well-documented degradation of permafrost, while strong increases of both population and livestock (> 60 million animals) in the recent decade put ecosystems in Mongolia under additional pressure from grazing and deforestation. With both changes accelerating in the recent decade, the delicate balance between climate forcing, ecosystem response and human land use has come under threat. In strong contrast, there is little quantitative knowledge how the sensitive ecosystems will react to these multi-source stresses, leaving risks for irreversible changes that will complicate sustainable land use in the future. Permafrost4Life aims at a better understanding and quantification of climate-ecosystem interaction, with a special focus on the role of the ground thermal regime within this interplay. The ultimate goal is to use this knowledge to help policy-making and land use management, with experiences stretching far outside Mongolia. To reach these goals we will use field experiments and state-of the art land system models. Permafrost4Life is a collaboration between research institutions from Norway and Mongolia, emphasizing the full equality of the research partners.