冻结季沱沱河源多年冻土区活动层土壤水分含量分析

Analysis of soil moisture content in the active layer in the permafrost region of the Tuotuo River source in frozen season

活动层含水量是表征多年冻土区气候、水文和生态过程的关键参数。长期以来,由于受多年冻土区活动层水分实测样点数量稀少的限制,各类基于遥感反演、模式模拟乃至数据融合和同化等手段生产的土壤水分空间数据均存在着较大的误差。2020年10—11月在青藏高原腹地(沱沱河源区)测定了1072组活动层土壤含水量数据并进行分析,探讨了该时段该区域活动层土壤水分的空间差异,并与全球陆面数据同化系统数据产品(GLDAS-Noah)和欧洲中期天气预报中心发布的第五代再分析资料(ERA5-Land)进行了对比分析。结果表明,在该区域平均厚度为2.72 m的活动层内,土壤质量含水量(总含水量)约为14.0%,活动层土壤含水量与植被发育情况存在正相关关系。除高寒沼泽草甸类型外,高寒草甸与高寒草原类型的活动层含水量随深度的增加呈现出先减小后增大的变化趋势。不同坡位类型的活动层含水量呈上坡位>下坡位>中坡位>平坡位,阳坡水分高于阴坡且两者活动层剖面水分变化相似。多年冻土区浅表层0~350 cm深度范围内的土壤含水量大于区内融区同深度的土壤含水量,两者土壤剖面水分分布均呈现出先增大后减小再增大的特征。该区域的GLDAS-Noah同化水分产品与实测数据对比的误差在10%以内,比ERA5-Land再分析土壤水分数据更为准确,但两种数据产品对土壤剖面上的水分垂直分布情况描述均与实测数据有较大差异。该研究结果可以为数据同化系统的模式冻融参数化方案优化及遥感水分产品研发提供科学依据。

The soil moisture content of active layer is a key parameter characterizing the climate,hydrology and ecological processes in permafrost regions.For a long time,due to the limited observations in permafrost re⁃gions,soil moisture datasets,e.g.,generated through remote sensing retrievement,model simulation,data fu⁃sion and assimilation have large biases.We collected 1072 active layer soil moisture samples in the permafrost area in the Tuotuo River source area in the hinterland of the Qinghai-Tibet Plateau during the comprehensive field campaign from October to November 2020.Based on these samples,we analyzed the active layer soil mois⁃ture characteristics in spatial,and evaluated two soil moisture products,i.e.,Global Land Data Assimilation System(GLDAS-Noah)and the reanalysis data released by the fifth-generation European Center for Medium-Range Weather Forecast(ERA5-Land).The results showed that in the investigated region,the average active layer thickness is about 2.72 m,and the soil mass moisture content(total moisture content)of the active layer is about 14.0%.The active layer soil moisture was positively correlated with vegetation development,except for alpine swamp meadow type.In the alpine meadow and alpine grassland environment,along with the soil depth increases,the soil moisture decreased first and then increased again.The active layer soil moisture content of the of different topography presents upper slope>lower slope>middle slope>flat slope.The moisture content in the sunny slope is higher than in the shady slope,but the patterns of soil moisture profile change with depths were similar.We also compared the soil moisture in a depth of 0~350 cm in the permafrost active layer and in the same depth in talik.The soil moisture profiles along the depth both increase first,then decrease,and then in⁃crease again.But the soil moisture content in the permafrost active layer is larger than that in the same depth of talik.Compared with measured data,GLDAS-Noah assimilated moisture product is biased less than 10%,which is more accurate in this area during the investigation period than ERA5-Land reanalysis soil moisture prod⁃uct,and both two soil moisture products cannot correctly describe the soil moisture profiles.The results provide a scientific basis for the optimization of model freeze-thaw parameterization in a data assimilation system and the development of remote sensing moisture products.