Evaluating controls of soil properties and climatic conditions on the use of an exponential filter for converting near surface to root zone soil moisture contents

•Impacts of soil properties and climatic conditions on Topt are assessed.•Topt at the same soil depth is mostly controlled by soil texture at the AWDN stations.•Topt at the same soil depth is mostly affected by precipitation at the SCAN stations.•Modeling results support observations from the AWDN and SCAN networks.