黄土高原表层土壤湿度与降水关系的分析

Analysis of the Relationship between Surface Soil Moisture and Precipitation over the Loess Plateau

使用黄土高原气象台站的土壤湿度和降水观测资料以及GLDAS和CMFD再分析资料,分析黄土高原地区土壤湿度与降水量的时空分布及变化特征,通过回归分析、格兰杰因果检验和奇异值分解(Singular value decomposition,SVD),研究土壤湿度与降水之间的关系,分析初始土壤湿度影响随后降水的时间尺度与空间范围。结果显示:黄土高原的土壤湿度与随后1~2个月降水回归分析的解释方差相对较高,较大值在夏秋季节(7-10月),黄土高原不同区域(Ⅰ区、Ⅱ区和Ⅲ区)的土壤湿度与随后21天降水相关的时间较全区域的多,时间较集中,说明黄土高原土壤湿度分布不均匀,不同区域差别较大,较大的滞后降水时间尺度适用于较大空间范围的分析。格兰杰因果检验表明黄土高原全区域秋季(10月、11月)的初始土壤湿度对随后1个月或2个月的降水有显著影响,在Ⅲ区8月土壤湿度对10月的降水也有显著影响,这与回归分析的结果一致。再分析资料的SVD分解的结果显示,1979-2014年7月黄土高原中部、北部和东部土壤较湿润时,8月西部和北部边缘的降水偏多;9月东部的土壤偏湿润,则10月黄土高原西部以及南北部的一些地区降水偏多。土壤湿度与降水的显著相关区域重叠部分较少,说明黄土高原土壤湿度对降水的影响存在一定程度的时空不对称性。

Observed soil moisture and precipitation as well as GLDAS and CMFD reanalysis data are used to analyze the spatial and temporal distribution and variation trend in the Loess Plateau region.Regression analysis,Granger causality test and singular value decomposition(SVD)are used to study the relationship between soil moisture and precipitation,and to analyze the temporal scale and spatial range of the influence of initial soil moisture on subsequent precipitation.The results show that the explained variance of the regression analysis of soil moisture and subsequent 1~2 months precipitation on the Loess Plateau is relatively high,with larger values in the summer and fall seasons(July,August,September,and October).That the correlation between soil moisture and the subsequent 21 days of precipitation in different regions of the Loess Plateau(zones I,II,and III)is more frequent and concentrated than that in the whole region.This indicates that soil moisture on the Loess Plateau is heterogeneous so that a larger lagged precipitation time scale is just suitable for analysis at larger spatial scales.The Granger causality test shows that the initial soil moisture in the fall(October and November)across the Loess Plateau has a significant effect on the precipitation in the following 1 or 2 months,and the soil moisture in August also has a significant effect on the precipitation in October in Area III,which is consistent with the results of the regression analysis.The result of the SVD decomposition shows that from 1979 to 2014,when soils in the central,northern,and eastern parts of the Loess Plateau are wetter in July,the precipitation in the western and northern margins of the plateau is accordingly more in August.A wetter soil in the eastern part of the plateau in September means more precipitation in the western part of the plateau,as well as some parts of the northern and southern parts of the plateau,in October.The significant correlation between soil moisture and precipitation has fewer overlapping regions,suggesting spatial and temporal asymmetry in the influence of soil moisture on precipitation on the Loess Plateau.