中国黄土高原塬区表层土壤水分盈缺状况的研究

Study on Water Deficit of the Topsoil over the Chinese Loess Plateau Mesa Region

陆地表层水分的盈缺直接关系到局地气候变化。本文利用黄土高原塬区初夏至盛夏期两次陆面过程野外试验(LOess Plateau land surface process field EXperi ment 2005,LOPEX05和LOPEX06)的野外试验观测资料,分析了试验期间黄土高原白庙塬区不同下垫面的水分蒸散和表层土壤水分盈缺状况。结果表明:在土壤水分比较充足的条件下,植被蒸腾增加量在正午时的峰值为0.05 mm.h-1,而较大降水发生后的首个晴日,冬小麦地和裸地的蒸散分别可达4.60 mm.d-1和3.70 mm.d-1。局地降水是影响陆面蒸散量变化的主要因素,而植被冠层的存在增加了陆面蒸散发量中的植物蒸腾量值。2006年4月下旬到7月中旬,裸地的水分缺失为16.3 mm.m-2,冬小麦地的水分缺失为39.9mm.m-2。其中缺失最严重的时间段为5月下旬到6月上旬,最大旬缺失量达16.5 mm.m-2,7月上旬和中旬,由于降水季节来临,土壤水分有少量盈余。在2005年7月中旬至8月下旬,玉米地和裸地的水分盈余分别为17.9 mm.m-2和25.3 mm.m-2。不同时间尺度的统计均表明,降水不仅是影响陆面蒸散量的主要因素,而且也是表层土壤水分盈缺的决定性因子。

Water deficit of the terrestrial topsoil is directly linked to the local climate variation. In this paper, the evapotranspiration and water deficit of the topsoil over different underlying surfaces were evaluated by the data collected during the LOess Plateau land surface process field EXperiment（LOPEX）, LOPEX05 and LOPEX06, which were conducted in the Chinese Loess Plateau Mesa Region. The maximal amount of evapotranspiration caused by canopy was about 0.05 mm·h^-1 at noon under the moderate soil water condition, whears the evapotranspiration could reach 4.60 mm·d^-1 in the first cloud-free day after a rainfall event over the winter wheat field, and it was 3.70 mm·d^-1 over bare soil land. Analyzed results indicate that the local precipitation was the main cause of evapotranspiration variation, whears canopy could enlarge the evapotranspiration. From the last-ten days of April to middle-ten days of July in 2006, the water deficit of topsoil were 39.9 mm·m^-2 in winter wheat field and 17.9 mm·m^-2 and 25.3 mm·m^-2 in bare soil land. The most serve soil water deficit period was from the last-ten days of May to the first-ten days of June, the maximum of ten days＇ could reach 16.50 mm·m^-2. Due to the coming of raining season, the soil water began to be surplus in the first and middle-ten days of July. From the middleten days of July to the last ten-days of August in 2005, water surplus of topsoil was 17.90 mm·m^-2 in underlying surface with corn and 25.30 mm·m^-2 over bare soil land. Statistical results at the different time scales indicate that the precipitation were main impact factor to evapotranspiration and determinant factor for water deficit of the terrestrial topsoil in Loess Plateau land mesa region.