Connectivity and topographic thresholds in bi-hourly soil moisture measurements along transects on a steep hillslope

Abstract

Summary Observation of temporal variations in soil moisture along transects is important when examining hydrological processes on a hillslope. Although there is substantial interest in characterizing catchment hydrology through an investigation of hydrologic connectivity, few attempts have been made to explore hydrologic connectivity within soil layers using soil moisture observations. Mathematical relationships among soil moisture differences are reproducible when Granger causality is defined within the context of hydrological connectivity because the process based transfer functions facilitate soil moisture predictions. Soil moisture time series along two transects on a steep hillslope were obtained using a multiplexed time domain reflectometry system during the growing season in June 2008 and 2009. The transfer function relationships between multiple soil moisture differences were delineated to determine a representative point for reliable time series modeling, and to establish the spatial pattern of areal clusters that will enable model identification and prediction. The impact of hillslope topography on the modeling of coupled soil moisture was highlighted by configuring the threshold behavior of model predictability. Results showed that soil moisture temporal relationships can be used for the prediction of volumetric soil moisture, within a specific area associated with representation point. Reliable relationships among soil moistures were apparent for points having greater upslope areas between 400 m 2 and 1000 m 2 .