Chinese Geographical Science ›› 2021, Vol. 31 ›› Issue (4): 696-710.doi: 10.1007/s11769-021-1218-4

• Articles • Previous Articles    

Identification of Suitable Hydrologic Response Unit Thresholds for Soil and Water Assessment Tool Streamflow Modelling

JIANG Liupeng1,2,3,4, ZHU Jinghai1, CHEN Wei1,2,3,4, HU Yuanman1,2,3, YAO Jing1,2,3, YU Shuai1,2,3, JIA Guangliang1,2,3, HE Xingyuan1,2,3,4, WANG Anzhi1,2,3   

  1. 1. Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China;
    2. University of Chinese Academy of Sciences, Beijing 100049, China;
    3. Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China;
    4. Shenyang Arboretum, Chinese Academy of Sciences, Shenyang 110016, China
  • Received:2020-12-24 Published:2021-06-28
  • Contact: HE Xingyuan, WANG Anzhi E-mail:hexy@iae.ac.cn;waz@iae.ac.cn
  • Supported by:
    Under the auspices of National Natural Science Foundation of China (No. 31901153); Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDA23070103)

Abstract: Use of a non-zero hydrologic response unit (HRU) threshold is an effective way of reducing unmanageable HRU numbers and simplifying computational cost in the Soil and Water Assessment Tool (SWAT) hydrologic modelling. However, being less representative of watershed heterogeneity and increasing the level of model output uncertainty are inevitable when minor HRU combinations are disproportionately eliminated. This study examined 20 scenarios by running the model with various HRU threshold settings to understand the mechanism of HRU threshold effects on watershed representation as well as streamflow predictions and identify the appropriate HRU thresholds. Findings show that HRU numbers decrease sharply with increasing HRU thresholds. Among different HRU threshold scenarios, the composition of land-use, soil, and slope all contribute to notable variations which are directly related to the model input parameters and consequently affect the streamflow predictions. Results indicate that saturated hydraulic conductivity, average slope of the HRU, and curve number are the three key factors affecting stream discharge when changing the HRU thresholds. It is also found that HRU thresholds have little effect on monthly model performance, while evaluation statistics for daily discharges are more sensitive than monthly results. For daily streamflow predictions, thresholds of 5%/5%/5% (land-use/soil/slope) are the optimum HRU threshold level for the watershed to allow full consideration of model accuracy and efficiency in the present work. Besides, the results provide strategies for selecting appropriate HRU thresholds based on the modelling goal.

Key words: hydrologic response unit, hydrological model, streamflow prediction, upper Hunhe River watershed, watershed representation, uncertainty