Preprints
https://doi.org/10.5194/gmd-2021-212
https://doi.org/10.5194/gmd-2021-212

Submitted as: model evaluation paper 26 Aug 2021

Submitted as: model evaluation paper | 26 Aug 2021

Review status: this preprint is currently under review for the journal GMD.

Improved Runoff Simulations for a Highly Varying Soil Depth and Complex Terrain Watershed in the Loess Plateau with the Community Land Model

Jiming Jin1,, Lei Wang2,3,, Jie Yang2,3, Bingcheng Si4, and Guo-Yue Niu5,6 Jiming Jin et al.
  • 1College of Resources and Environment, Yangtze University, Wuhan 430100, Hubei, China
  • 2College of Water Resources and Architectural Engineering, Northwest A & F University, Yangling 712100, Shaanxi, China
  • 3Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education, Northwest A & F University, Yangling 712100, Shaanxi, China
  • 4Department of Soil Science, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada
  • 5Biosphere 2, the University of Arizona, Tucson, AZ 85623, USA
  • 6Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721, USA
  • These authors contributed equally to this study.

Abstract. This study aimed to improve runoff simulations and explore deep soil hydrological processes for a watershed in the center of the Loess Plateau (LP), China. This watershed, the Wuding River Basin (WRB), has very complex topography, with soil depths ranging from 0 to 197 m. The hydrological model used for our simulations was the Community Land Model (CLM) version 5 developed by the National Center for Atmospheric Research. Actual soil depths and river channels were incorporated into CLM to realistically represent the physical features of the WRB. Through sensitivity tests, CLM with 150 soil layers produced the most reasonable results and was adopted for this study. Our results showed that CLM with actual soil depths significantly suppressed unrealistic variations of the simulated sub-surface runoff when compared to the default simulations with a fixed soil depth of 8 m. In addition, CLM with higher-resolution soil layering slightly improved runoff simulations, but generated simulations with much smoother vertical water flows that were consistent with the uniform distribution of soil textures in our study watershed. The runoff simulations were further improved by the addition of river channels to CLM, where the seasonal variability of the simulated runoff was reasonably captured. Moreover, the magnitude of the simulated runoff remarkably decreased with increased soil evaporation by lowering the soil water content threshold, which triggers surface resistance. The lowered threshold was consistent with the loess soil, which has a high sand component. Such soils often generate stronger soil evaporation than soils dominated by clay. Finally, with the above changes in CLM, the simulated total runoff matched very closely with observations. When compared with those for the default runoff simulations, the correlation coefficient, root-mean-square error, and Nash Sutcliffe coefficient for the improved simulations changed dramatically from 0.02, 10.37 mm, and −12.34 to 0.62, 1.8 mm, and 0.61. The results in this study provide strong physical insight for further investigation of hydrological processes in complex terrain with deep soils.

Jiming Jin et al.

Status: open (until 01 Nov 2021)

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Jiming Jin et al.

Jiming Jin et al.

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Short summary
This study aimed to improve runoff simulations and explore deep soil hydrological processes for a highly varying soil depth and complex terrain watershed in Loess Plateau, China. The actual soil depths and river channels were incorporated into the model to better simulate the runoff in this watershed. The soil evaporation scheme was modified to better describe the evaporation processes. Our results showed that the model significantly improved the runoff simulations.