This discussion paper is a preprint. A revision of the manuscript is under review for the journal Hydrology and Earth System Sciences (HESS).
Land Surface Model Representation of the Mutual Information
Context between Multi-Layer Soil Moisture and
Evapotranspiration
Jianxiu Qiu1,2,Wade T. Crow3,Jianzhi Dong3,and Grey S. Nearing4Jianxiu Qiu et al. Jianxiu Qiu1,2,Wade T. Crow3,Jianzhi Dong3,and Grey S. Nearing4
1Guangdong Provincial Key Laboratory of Urbanization and Geo-simulation, School of Geography and Planning, Sun Yat-sen University, Guangzhou, 510275, China
2Southern Laboratory of Ocean Science and Engineering (Guangdong, Zhuhai), Zhuhai, 519000, China
3USDA ARS Hydrology and Remote Sensing Laboratory, Beltsville, MD 20705, USA
4Department of Geological Sciences, University of Alabama, AL 35487, USA
1Guangdong Provincial Key Laboratory of Urbanization and Geo-simulation, School of Geography and Planning, Sun Yat-sen University, Guangzhou, 510275, China
2Southern Laboratory of Ocean Science and Engineering (Guangdong, Zhuhai), Zhuhai, 519000, China
3USDA ARS Hydrology and Remote Sensing Laboratory, Beltsville, MD 20705, USA
4Department of Geological Sciences, University of Alabama, AL 35487, USA
Received: 05 Jun 2019 – Accepted for review: 12 Jul 2019 – Discussion started: 15 Jul 2019
Abstract. Soil moisture (θ) impacts the climate system by regulating incoming energy into outgoing evapotranspiration (ET) and sensible heat flux components. Therefore, investigating the coupling strength between θ and ET is important for the study of land surface/atmosphere interactions. Here, we use in-situ AmeriFlux observations to evaluate θ/ET coupling strength estimates acquired from multiple land surface models (LSMs). For maximum robustness, coupling strength is represented using the sampled normalized mutual information (NMI) between θ estimates acquired at various vertical depths and surface flux represented by fraction of potential evapotranspiration (fPET, the ratio of ET to potential ET). Results indicate that LSMs are generally in agreement with AmeriFlux measurements in that surface soil moisture (θS) contains slightly more NMI with fPET than vertically integrated soil moisture (θV). Overall, LSMs adequately capture variations in NMI between fPET and θ estimates acquired at various vertical depths. However, one model – the Global Land Evaporation Amsterdam Model (GLEAM) – significantly overestimates the NMI between θ and ET and the relative contribution of θS to total ET. This bias appears attributable to differences in GLEAM's ET estimation scheme relative to the other two LSMs considered here (i.e., the Noah with Multi–parameterization option and the Catchment Land Surface Model). These results provide insight into improved LSM model structure and parameter optimization for land surface-atmosphere coupling analyses.
Accurately describe how the constraint of soil moisture (θ) on evapotranspiration (ET) varies as θ is integrated over deeper depth is key to understand how θ regulates land-atmosphere interaction. Using AmeriFlux observations as benchmark, we examine whether entropy-based estimates of LSM surface θ versus ET and vertically integrated θ versus ET coupling accurately reflect observations acquired at ground sites. The work provides insight into land-atmosphere coupling analysis and LSM development.
Accurately describe how the constraint of soil moisture (θ) on evapotranspiration (ET) varies...