Research Of Surface Air And Ground Temperature Change For Degraded Grassland In The Temperare Grassland Region Of China

Investigating the interactions between global change and terrestrial ecosystem is a critical focus for global change studies. The relationship between terrestrial ecosystem and climate change is an important aspect of climate change studies. As one of the most widespread vegetation types worldwide, grassland vegetation activity is not only affected by climate change, but also plays an important role in the change of regional climate. Investigating the effects of temperate grassland vegetation change on regional climate will be helpful to improve the research on the relationship between vegetation and climate change, and to provide a scientific basis for ecological environment construction in the temperate grassland region. By using vegetation and meteorological data in the temperate grassland region of China, this study firstly investigates the relationship between grassland vegetation and climate change in the temperate grassland region. Based on the Chinese Academy of Sciences Changling station of grassland and agroecology, this study mainly focuses on the research of surface air and ground temperature change for degraded grassland in the Songnen plain.The results showed that both the air and soil temperatures showed significant warming trends during the past decades in the temperate grassland region of China. But the increase of minimum air temperature was faster than that of maximum air temperature, which is called the asymmetric warming of surface air temperature. In addition, we found the increase of soil temperature was larger than that of air temperature, which is another asymmetric warming pattern of soil and air temperatures. Due to the effect of human activities in the temperate grassland region of China, grassland vegetation in this region experienced serious degradation in the past decades. For the unchanged patches of grasslands in this region, the growth of grassland vegetation became well, with the largest increase of vegetation cover for temperate meadow. The increase of spring surface air temperature, especially the minimum air temperature is beneficial for the growth grassland vegetation. There also exist asymmetric effects of summer maximum and minimum air temperatures on temperate grassland vegetation. The increase of summer temperature could prohibit the growth of temperate desert grassland, but the increase of summer precipitation will promote its growth. In the temperate grassland region of China, the impacts of different grassland types and vegetation cover changes on observed surface warming were different. The observed warming related to the grassland vegetation was the weakest for temperate meadow and the strongest for temperate desert steppe. During the growing season, when the grassland vegetation has the stronger seasonal changes, the effect of seasonal vegetation cover change on temperature change becomes more obvious. In August and September, temperate meadow has a weak cooling effect on the surface air temperature. Because of the limited soil moisture and little evaporative cooling feedback, the cooling effects of temperate steppe and temperate desert steppe on the surface air temperature were limited.Based on the results of site experiment, grassland degradation in Songnen plain will increase both growing season air temperature and soil temperature. For soil and air temperatures, bare land has the largest temperature values, followed by heavily degraded, slightly degraded and un-degraded grasslands. With the degradation of grassland in Songnen plain, diurnal air temperature range increased. In addition, grassland degradation has a larger warming effect on soil temperatures than air temperatures, which results in the increase of temperature difference between soil and air temperature. Similar to air temperatures, there are asymmetric effects of grassland degradation on soil temperatures during the daytime and night-time, which results in the increase of soil diurnal air temperature range. During the growing season, grassland degradation could increase the land surface albedo but reduce surface soil water content, which thus affect the process of surface energy balance. As the degradation of grassland vegetation, land surface albedo increased, surface net radiation decreased, but the soil heat flux increased. Grassland degradation exposed more soil surface, so the surface soil receives more solar radiation which results in a larger soil temperature for the degraded grasslands. Grassland degradation also could decrease the soil water content, which reducing the proportion of net energy partitioned into latent heat. Therefore, sensible heat flux increased with the degradation of grassland vegetation, accounting for the warming impact of grassland degradation on surface air temperature. For un-degraded grasslands, due to high soil water content, larger latent heat loss through evapotranspiration further accounts for the low soil temperatures.