Water And Heat Process Of Alpine And Swamp Meadow In Permafrost Zones And Response To The Global Warming In The Source Region Of Yangtze River

As a plateau region of highest elevation and most complicated landform with its special geographical position and geomorphological characteristics, Qinghai-Tibetan Plateau plays an important role in global climate change aspects. Also as an area with fragile ecosystems and sensitive response to the global climate change, Qinghai-Tibetan Plateau is vulnerable to the interference from human activities and the global warming impact. Soil water heat process is one of the most important uncertain factors to the hydrology and energy cycles in permafrost regions, frozen soil get climate, hydrology, ecology, and environment together by means of water heat cycle process.Consequently, to investigate the influence of vegetation degradation on soil water and heat process and the effect of temperature rising on permafrost water and heat process of grassland ecosystem, process of water and heat change under different vegetation coverage of alpine meadow and process of water and heat change under different temperature increasing situations of alpine meadow and swamp meadow have been long-term monitored.1. To investigate the influence of vegetation coverage on water and heat process of active layer, the results show that:(1) The dates of the active layers beginning to freeze and thaw continuously become earlier than as usual with the reduction of vegetation coverage, and the frozen duration shorten;(2) Soil moisture and temperature changing rate of the active layers are enhanced with the reduction of vegetation coverage, and vegetation has inhibitory effect on the changing rate of soil moisture and temperature;(3) Impacts of vegetation coverage on soil water and heat during summer thawing process and autumn freezing process are greater than those during winner cooling process and spring warming process, meanwhile, impact on soil water and heat during summer thawing process is markedly greater than that during autumn freezing process.(4) In order to seek water and thermal coupling regression model appropriate for permafrost region, non-linear fitting of soil temperature (T) and moisture (θ_v) have been applied, then gained regression model ofθ_v = p1/{1 + exp[p2×(t-p3)]} + p4 (where p1, p2, p3, p4 are fitting parameters), the feasibility of which were determined through validity testing between calculated and observed data.2. To investigate the impact of climate warming on water and heat process of active layer of alpine and swamp meadow, the results show that:(1) Influence of climate warming on water and heat process of active layer of swamp meadow:i. As air temperature increased, the dates of active layer beginning to freeze became slower and the duration of freezing process prolonged, while the dates beginning to thaw became earlier and the duration of thawing process had little difference, frozen duration became shorten and soil temperature changing rate became slowly, however, un-frozen duration became longer and soil temperature changing rate became rapidly;ii. As air temperature increased, there had great different variation of moisture distribution in soil profile, capping and un-capping greenhouse soil moisture decreased with soil depths increasing and the decreasing rate of capping greenhouse is larger than that of un-capping greenhouse, however, outdoor situation had a highest moisture aquifer in soil surface, a higher moisture aquifer below 110cm and a lower moisture aquifer in 65cm~75cm, meanwhile, soil moisture changing rate of freezing and thawing process were corresponding to moisture distribution of the soil profile, which increased in shallow depths and deceased in deep depths, and had little difference in frozen duration;(2) Influence of climate warming on water and heat process of active layer of alpine meadow:i . As air temperature increased, similar to that of swamp meadow, the dates of active layer beginning to freeze became slower and temperature changing rate became slowly, while the dates beginning to thaw became earlier and temperature increasing rate became rapidly, however, un-frozen duration became longer and prolonged with depths increased;ii .The maximum soil moisture of capping, un-capping and outdoor situation all appeared in 20cm depth, which decreased to 10-15% when active layer froze, active layer thawing soil moisture of different depths of capping greenhouse was larger than active layer freezing.3. Applied SHAW model to simulated soil thermal characteristic of active layer of alpine meadow, the results show that:The simulated temperature by SHAW model inosculated with observed temperature, and the changing tendency was basically identical, simulated temperature was larger than observed when active layer froze; Soil temperature modeling NSE efficiency coefficient reached 0.7 and correlation efficient exceed 0.85 of the whole profile except of deep depths of 120cm. In one word, SHAW model could successfully simulate the soil temperatures of the active layer and thawing and freezing process.