陕北黄土区微地形土壤水分对降水特征的响应

Response of Soil Moisture of Microtopography on Precipitation Characteristics in the Loess Region of Northern Shaanxi

利用标准化降水指数分析了吴起县1957—2012年的全年、生长季的降水特征，以及缓坡和陡坡不同微地形土壤水分在2008—2012年生长季的动态变化特征，结果表明：吴起县1957—1986年的降水波动较大，出现极端、严重干旱和湿润年份，但1987年以来则表现为轻微干旱、湿润或正常；生长季标准化降水指数与各点土壤水层厚度变化值呈正相关关系，与塌陷、缓坡的相关程度（R^2）低于0.8，与切沟、缓台及浅沟的相关程度介于0.8-0.9之间，与其他各点的相关程度大于0.9；生长季各点土壤水层厚度变化值存在显著差异，且缓坡、塌陷和缓台的值显著高于其他各点。

Standard precipitation index （SPI） was used to analyze the annual and growing season precipitation conditions from 1957 to 2012 based on the precipitation data of meteorological station in Wuqi County. The correlation analysis was used between the SPI and the soil water layer thickness of the microtopographies during 2008—2012. The results showed that the precipitation fluctuation was larger from 1957 to 1986 than that from 1987 to 2012. The extreme and severe drought years appeared in 1957—1986, but those did not appear during 1987—2012; there was positive correlation between the SPI of growing season and the change value of soil water layer thickness of microtopographies. The SPI of growing season had the lower correlation degree （R^2〈0.8） with the gentle slope and sink hole of steep slope, but the R^2 lay between 0.8 and 0.9 with gully, platform and ephemeral gully. The SPI of growing season had the larger correlation degree （R^2〉0.9） with scarp, sunny uniform slope and half sunny uniform slope; and the difference among the change value of soil water layer thickness in the all monitoring points was significant in the growing season, and the mean soil water layer thickness of gentle slope, sink hole and platform was larger than those of other monitoring points.