青藏高原中部BJ站土壤湿度不同时间尺度的变化

青藏高原土壤湿度的时空变化在高原能水循环中起着重要作用。利用GAME-Tibet期间观测的青藏高原中部BJ站2001年1月1日~2005年12月31日00:00~230:0逐时高分辨率土壤湿度资料,分析了4~210 cm深度土壤湿度的日、季节和年际等不同时间尺度的变化特征。结果表明:(1)4 cm深度土壤湿度日变化显著2,0~210 cm深度土壤湿度日变化微弱;土壤湿度日振幅随土壤深度的增加逐渐衰减,但在210 cm深度又出现增加的趋势;4 cm、20 cm、60 cm、100 cm1、60 cm和210cm深度土壤湿度的平均日振幅分别为0.97%、0.22%、0.03%、0.01%、0.01%和0.03%。(2)根据土壤湿度在时间尺度和垂直剖面上的变化特征,将土壤湿度年内的变化过程划分为积累期(3~8月)、衰减期(8~12月)和相对稳定期(12~3月)3个阶段。(3)2001~2005年,BJ站4 cm、20 cm、60 cm、100 cm和160 cm深度土壤湿度8月的平均值表现为线性增加的趋势,210 cm深度土壤湿度8月的平均值则呈现出线性减小的趋势;湿季,土壤湿度显著地受到降水的影响,干季,土壤湿度主要受土壤温度的影响。

Variations in Soil Moisture at Different Time Scales of BJ Site on the Central Tibetan Plateau

The temporal and spatial variations in soil moisture play an important role in the water and energy cycle on the Tibetan Plateau.Based on the observed high resolution hourly soil moisture data(4-210 cm) obtained by GAME-Tibet at BJ site on the central Tibetan Plateau from 1 January 2001 to 31 December 2005,the diurnal,seasonal and interannual variation characteristics in soil moisture are analysed.The results are as follows.(1) The average diurnal variation in soil moisture at 4 cm soil depth is evident.However,the average diurnal variation in soil moisture at 20-210 cm soil depth is extremely weak.The average diurnal amplitude(ADA) of soil moisture decreases gradually with the increase of soil depth.But the ADA of soil moisture at 210 cm soil depth increases slightly.The ADA of soil moisture at 4,20,60,100,160 and 210 cm soil depth are 0.97,0.22,0.03,0.01,0.01 and 0.03%,respectively.(2) According to the variation characteristic in soil moisture at different time scales and vertical section,the variation in soil moisture throughout the year can be divided into three phases: accumulation phase(March to August),attenuation phase(August to December) and the relatively stable phase(December to March),respectively.(3) During the period 2001 to 2005,the soil moisture at 4,20,60,100 and 160 cm soil depth in August increases with a linear trend.Conversely,the soil moisture at 210 cm soil depth in August decreases with a linear trend.During the wet season,soil moisture has an obvious response to precipitation;however,during the dry season,soil moisture affected by soil temperature significantly.