不同植被盖度变化下活动层水热过程是多年冻土区水能循环中一个重要的不确定因素.为了研究植被盖度变化对活动层水热过程的影响,在青藏高原多年冻土区,选择坡向、坡型和坡度趋于一致植被覆盖度分别为92%、65%、30%的坡面建立天然径流观测场,观测多年冻土活动层中的地温和水分状况.结果表明:活动层开始冻结和消融时间随着植被盖度的减少不断提前,且冻结持续时间缩短;随着植被盖度减小,活动层地温水分变化速率增大,植被起到抑制土壤地温水分变化速率的作用;植被盖度对夏季融化过程和秋季冻结过程活动层地温和水分的影响明显大于冬季降温和春季升温过程,对融化过程的影响较冻结过程更明显.

 The effect of vegetation coverage on the soil water heat process is one of the most important uncertain factors to the hydrology and energy cycles in permafrost regions.To investigate the process of water and heat changes under different vegetation coverage,three runoff plots were established on the places where the topography was of the same slope,direction and shape and where the vegetation coverage was 92%,65% and 30%,respectively,in permafrost region of the Tibetan Plateau,which can be used for observing the soil moisture and heat condition of active layers.The results show that,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 durations shorten;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;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.