Resistivity is used as a tool to evaluate the variability of soil water content

Resistivity is used to evaluate soil water content(SWC),which has the advantages of not causing soil disturbance and in low price.It is an effective way to assess the SWC variability.This paper aims to evaluate the variability of loess slope SWC through the change of resistivity.It provides a simple way for long term SWC monitoring to solve the expensive cost of deploying moisture sensors.In this context,geoelectric and environmental factors such as soil temperature and SWC were monitored for three years.The prediction model of apparent resistivity and SWC was calibrated.The post processing of geoelectric data was introduced.In addition,the SWC collected by Time-Domain Reflectometry(TDR)was used to verify the feasibility of electrical resistivity tomography(ERT)data.The SWC variability in the process of rainfall,the evolution of four seasons,and the alternation of drying and wetting were evaluated.The research results show that:i)the SWC monitored by ERT and TDR can reflect the response and hysteretic effect of water content at 0.5-3.0 m depth.ii)The moisture content monitored by ERT reflects that the soil is relatively wet in summer and autumn and dry in winter and spring.iii)From 2017 to 2020,the SWC increased in August,and the soil became dry in January.iv)Two areas with high SWC and three areas with low SWC on loess slope are reflected by resistivity.The outcome can provide the change information of SWC to a great extent without excavating boreholes.

Spatiotemporal variations in moisture conditions across Monsoon Asia during the last 500 years

Spatial and temporal variations in moisture conditions across monsoon Asia were investigated using 347 Monsoon Asia Drought Atlas(MADA)grid points and 100 Chinese historical documents sites during the years 14702000.We applied Rotated Empirical Orthogonal Function(REOF)analysis to evaluate spatial moisture variability during the past 530 years.The first 13 principal components together explained 61.35%of the total variance,with the First Principal Component(PC1)accounting for 14.1%.After varimax rotation to the first 13 EOFs,we obtained new time series and spatial patterns.These patterns divided monsoon Asia into 13 regions with coherent moisture variability.Drought events were analyzed within these 13 regions.The results indicate that there has been a prominent drying trend in eastern and central Mongolia,Southeast Asia and east China during the last 50 years.Conversely,India and the Tibetan Plateau show a significant in crease in moisture around the late 20th century.We found four drought periods,A.D.16251644,A.D.17101729,A.D.1920s,and A.D.19751999 occurred widely across monsoon Asia during the past 530 years.On inter-annual time scales,moisture variations in the northwest region of monsoon Asia,the Indian subcontinent and Southeast Asia are influenced by the El Ni o-Southern Oscillation(ENSO).Thirty-year running correlation coefficient diagnostic analysis revealed that moisture variability in monsoon Asia is associated with the Pacific Decadal Oscillation(PDO).