三峡山地不同坡位土壤水分的时序变化研究

土壤水分是维持森林生态系统可持续的重要因子，降水作为土壤水分最主要的补给来源，定量认识两者的关系对深入了解土壤水分入渗及产流汇流等生态水文效应和区域水平衡至关重要.该文采用时间序列法分析了2018年—2019 年三峡山地大老岭林区典型小流域土壤含水量和降水之间的相关关系，结果表明：1) 研究区降水过程无显著自相关性，而土壤含水量呈现高度自相关性，且随时间尺度缩小不断增强；2) 降水量与土壤水分含量同消同涨，两者之间存在协相关关系，月尺度上土壤含水量与降水相关性较弱，日尺度上二者相关性呈明显的“单锋型”，小时尺度上降水序列和土壤水分序列相关性在降雨事件发生后2～4 h最显著；降雨72 h后，各深度土层相关系数差异明显减小.3) 在不同时间尺度下，不同深度土层土壤含水量与降水的协相关性变化趋势表现出较强的一致性，随土壤深度增加，土壤含水量与降水的相关性降低，且水分变化对降雨滞后性增加.4) 不同坡位土壤水分与降水的协相关性差异显著.坡下土壤含水量对降水的响应强烈，而坡上两者相关系数偏低.5) 土壤水分序列与降水序列协相关性在不同时间尺度有所差异，小时尺度和天尺度两者协相关性较为显著且均随着时间推移呈先增大后减小的特征，而月尺度两者相关性则表现为随滞后时间距增加而单调递减趋势.

Time series analysis of soil moisture content at different slope positions in the Three Gorges of Yangtze River

Variations and response to precipitation of soil moisture content are of great significance to forestry development and soil and water conservation in mountainous area.Time series analysis can reflect the relationship between two random variables， so it can be used to analyze the response of soil moisture sequence to precipitation sequence. However， the correlation between them needs to be discussed across different temporal scales. By using time series analysis， the relationship between soil moisture content and precipitation in the Dalaoling Forest Region of the Three Gorges Mountainous region were studied from 2018 to 2019. The results indicated as follows. 1)Precipitation was not an autocorrelation series， while soil moisture content was. With the temporal scale reducing， the autocorrelation was continuously enhanced. 2)There was a correlation between precipitation and soil water content， whose value was weak on the monthly scale. On the daily scale， the correlation between them was obviously single spike type， which means it was low on the day of precipitation and reached the highest value on the day after rain event. With increasing of delay time， the correlation showed a markable decreasing trend. On the hourly scale， the correlation between precipitation and soil moisture was the most significant after 2-4 hours of precipitation event. After 72 hours， the difference of correlation coefficient among different soil layers reduced obviously.3)Under different temporal scales， the dynamic change of correlation between soil water content and precipitation showed strong consistency in different depths， but the deep soil layer had little connection with precipitation. In the soil depth of 0-20 cm there was a significant correlation with precipitation， which exhibited transitional characteristics in 40 cm. And in 80 cm soil layer， the influence of precipitation was not evident， and the response time slightly lagged behind the upper layer. 4)The correlation between soil moisture and precipitation at different slope positions was significantly distinct. The lower position along the slope responded to rainfall instantaneously. Whereas the correlation coefficient was low in the upper position. 5)The correlation between soil moisture and precipitation had a great difference in different temporal scales the correlation on the hourly and daily scales both showed a fluctuation trend of increasing in the beginning and then decreasing over time. While on the monthly scale the correlation showed a monotonic decreasing trend with adding time.