[H-CG23] Adaptation to climate change and its social implementation

[HCG23-03] Simulation of the effects of climate change and grazing intensity on permafrost degradation in Mongolian grassland ecosystems

*Qinxue Wang¹, Tomohiro OKADERA¹, Tadanobu NAKAYAMA¹, Zhigang SUN², Tonghua WU³, Ochirbat BATKHISHIG⁴, Masataka WATANABE⁵ (1.National Institute for Environmental Studies, 2.Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 3.Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, 4.Institute of Geography and Geoecology, Mongolian Academy of Sciences, 5.Research and Development Initiative, Chuo University)

Keywords:Grassland ecosystems, Grazing intensity, permafrost degradation

To detect the effects of climate change on the degradation of permafrost in terrestrial ecosystems, we have constructed a permafrost monitoring network in north-central Mongolia since 2007. The network includes eight boreholes and three meteorological stations for measuring monitoring ground temperature profiles in various terrestrial ecosystems. Observations showed that permafrost beneath grassland ecosystems is degrading more rapidly than other ecosystems, such as forests and wetlands (Wang et al., 2022). The purpose of this study is to use the SHAW (Simultaneous Heat And Water) model (Flerchinger et al., 1989, 2017) to elucidate the effects of climate change and grazing intensity on the degradation of the permafrost beneath the Mongolian grassland ecosystem. We, at first, calibrated the SHAW model using observational data from 2008 to 2020, and then, the calibrated model was used to simulate the effects of climate change and grazing intensity on permafrost across different scenarios.
To evaluate the impacts of climate change on permafrost degradation, four temperature increase scenarios and five precipitation fluctuation scenarios were designed. The temperature increase scenarios include the current temperature (Ta, °C) and three other scenarios reported in the IPCC AR6 WGI Technical Summary: the “SSP1-1.9 scenario” under 1.5 °C, “SSP1-2.6” over 1.5°C, and “SSP5-8.5” over 4.0°C by the end of this century (IPCC, 2021). The precipitation fluctuation scenarios include the current precipitation (P, mm) and four other scenarios (0.50×P, 0.75×P, 1.25×P, and 1.50×P, mm). In addition, to evaluate the impact of grazing intensity on permafrost degradation, four scenarios (no grazing, light grazing, moderate grazing, and heavy grazing) were designed.
Numerical experiments show that warming, especially precipitation fluctuations, plays an important role in maintaining the active layer of permafrost. Although the grazing has no obvious effects on the degradation of permafrost under wet conditions of high soil moisture, overgrazing under dry conditions with low soil moisture can obviously accelerate the degradation of permafrost. Overall, this numerical experiment suggests that the permafrost beneath Mongolian grassland ecosystems will become more vulnerable when drought and overgrazing associated with warming occur simultaneously. Therefore, controlling the intensity of grazing may be important for maintaining permafrost.
References:
Wang, Q., T. Okadera, M. Watanabe, T. Wu, B. Ochirbat (2022): Permafr. Periglac. Process, 33 (4): 406-424. https://doi.org/10.1002/ppp.2161
Flerchinger, G.N., K.E. Saxton (1989): Transactions of the ASAE. 32(2): 0565-0571. https://doi.org/10.13031/2013.31040
Flerchinger, G.N. (2017): The Simultaneous Heat and Water (SHAW) Model: Technical Documentation. https://www.ars.usda.gov/ARSUserFiles/20520500/SHAW/ShawDocumentation.30.pdf
IPCC, 2021: Technical Summary, Climate Change 2021: The Physical Science Basis. https://www.ipcc.ch/report/ar6/wg1/chapter/technical-summary/