青藏高原及其典型区域土壤湿度的分布和变化特征

Distribution and variation of soil moisture over the Tibetan Plateau and its typical areas

基于土壤湿度融合分析产品及气象观测资料,分析了青藏高原及其典型区域的土壤湿度分布特征以及影响因素.结果表明:青藏高原土壤湿度与高原降水季节有较好的对应关系,降水量多的季节对应大的土壤湿度,反之亦然,即夏季土壤湿度最大,春季和秋季次之,冬季最小;高原外围土壤相对较湿,中部较干,夏季土壤高湿度区从藏东南向西北、塔里木盆地向藏东北扩展,冬季土壤高湿度区向藏东南和塔里木盆地收缩;土壤湿度垂直层次呈现出浅层和深层低、中间层高的特点,从浅层到深层土壤湿度的变化幅度逐渐减小;高原典型区域土壤湿度逐日变化规律与高原区域平均的土壤湿度时间演变接近一致,降水量的多少和湿润区、半干旱区土壤湿度高低值有较好的对应关系,湿润区垂直梯度大,干旱区和半干旱区垂直梯度小;蒸发量、风速、气温以及植被状况均会影响到土壤湿度的分布特征.

With soil moisture dataset derived from China Land Data Assimilation System of China Meteorological Administration（ CLDAS-CMA）,the spatiotemporal and vertical distribution of soil moisture over the Tibetan Plateau（ TP） and its typical areas with influencing factors have been investigated for period of July 1,2009 to June 30,2010.Results show that soil moisture corresponds well to the precipitation over the Tibetan Plateau.Soil tends to be wet during the rainy season with large precipitation and vice versa. Soil moisture persists significant seasonal variation,which is highest in summer,followed by that in spring and autumn,while it is lowest in winter.With the rise of air temperature,March to August has become the period with increasing soil moisture and the areas with high soil moisture has expanded from the southeast part of Tibet to the northwest part of the Plateau,as well as from Tarim Basin to the northeastern of Tibet.As for the vertical distribution,soil moisture tends to be high at interlayer,and low at shallow layer and deep layer,with a gradual decreasing trend in variation magnitude from shallow layer to deep layer.The distribution of soil moisture at typical areas over the TP presents similar temporal variation tendency as the regional average soil moisture for the entire Plateau. Season with large precipitation is corresponding to the season with large soil moisture in humid and semi-arid areas.Humid areas has bigger vertical gradient in soil moisture compared with arid and semi-arid areas. Meteorological variables such as evaporation,wind speed,average air temperature and vegetation coverage have some influence on the distribution of soil moisture.