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[HCG26-P06] Impacts of permafrost thawing and their adaptation strategies in Mongolian grasslands
Keywords:permafrost thawing, Mongolian grasslands, adaptation strategies
More than 70% of Mongolian territory is covered by grasslands. Grasslands are the most important resource for the life of nomads. Under the grassland, the permafrost exists in the northern part of Mongolia, where the annual average temperature is below 0°C. According to data analysis of the six stations with the longest meteorological observation history (Ulaanbaatar, Balloon Hara, Choir, Sainshand, Zamiin-Uud and Mandalgovi) in Mongolia, the average annual air temperature rose by about 2.8°C during the 75 years from 1945 to 2019, which was much larger than that of world average. The permafrost thawing due to global warming is considered to cause the changes in water cycle, and finally, to make influences on the productivity and grazing capcity of grasslands.
Since 2009, we have observed the ground temperature in various terrestrial ecosystems such as forests, grasslands, and wetlands in northern Mongolia to detect the effect of global warming on the thawing of permafrost. From the observation data, indicators such as the mean annual ground temperature (MAGT) at a depth of zero annual amplitude and the active layer thickness (ALT) were calculated, and the melting speed and fluctuation range of permafrost were analyzed. As a result, it was found that the degradation of permafrost in grasslands was more remarkable than that in other ecosystems. In addition, the result of numerical experiments using the SHAW (Simultaneous Heat and Water) model (Flerchinger and Saxton, 1989) showed that the drought caused by the global warming will accelerate the thawing of permafrost, and if the overgrazing occurs simultaneously, it may further accelerate the permafrost thawing.
Based on the data analysis and numerical experiments, we found that if the permafrost thawing, the water circulation will change as the melted water evaporates or flows into rivers and lakes. In addition, if the ALT is less than 1-2 m from the ground surface, the root layer contains water melted from snow and frozen soils, so the vegetation can obtain stable water. However, if the ALT was larger than 2-2.5 m, the melted water from frozen soils is difficult to reach the root layer, so the vegetation relies only on rainwater, which is much unstable. In other words, it was found that the thawing of permafrost caused the change in water resources such as soil water, runoff, and groundwater, as a result, it will cause the change in grassland productivity and grazing capacity.
To keep a high-productive grassland ecosystem, it is important to reduce the stress due to overgrazing and over-utilization. In addition, several adaptation measures, such as proper management of the number of livestock, improvement of grassland utilization rate and pasture harvest rate, introduction of feed and water resources from outside, and effective use of groundwater by digging wells can be considered. However, it is essential to consider the advantages and disadvantages, as well as the feasibility of these countermeasures. In the future, we would like to evaluate the effects of these adaptation measures by using the evaluation model that we have developed so far.
Since 2009, we have observed the ground temperature in various terrestrial ecosystems such as forests, grasslands, and wetlands in northern Mongolia to detect the effect of global warming on the thawing of permafrost. From the observation data, indicators such as the mean annual ground temperature (MAGT) at a depth of zero annual amplitude and the active layer thickness (ALT) were calculated, and the melting speed and fluctuation range of permafrost were analyzed. As a result, it was found that the degradation of permafrost in grasslands was more remarkable than that in other ecosystems. In addition, the result of numerical experiments using the SHAW (Simultaneous Heat and Water) model (Flerchinger and Saxton, 1989) showed that the drought caused by the global warming will accelerate the thawing of permafrost, and if the overgrazing occurs simultaneously, it may further accelerate the permafrost thawing.
Based on the data analysis and numerical experiments, we found that if the permafrost thawing, the water circulation will change as the melted water evaporates or flows into rivers and lakes. In addition, if the ALT is less than 1-2 m from the ground surface, the root layer contains water melted from snow and frozen soils, so the vegetation can obtain stable water. However, if the ALT was larger than 2-2.5 m, the melted water from frozen soils is difficult to reach the root layer, so the vegetation relies only on rainwater, which is much unstable. In other words, it was found that the thawing of permafrost caused the change in water resources such as soil water, runoff, and groundwater, as a result, it will cause the change in grassland productivity and grazing capacity.
To keep a high-productive grassland ecosystem, it is important to reduce the stress due to overgrazing and over-utilization. In addition, several adaptation measures, such as proper management of the number of livestock, improvement of grassland utilization rate and pasture harvest rate, introduction of feed and water resources from outside, and effective use of groundwater by digging wells can be considered. However, it is essential to consider the advantages and disadvantages, as well as the feasibility of these countermeasures. In the future, we would like to evaluate the effects of these adaptation measures by using the evaluation model that we have developed so far.