Abstract
Abstract. The coupled atmospheric–hydrologic modeling system is an effective way to improve the accuracy of rainfall–runoff modeling and extend the lead time in real-time flood forecasting. The aim of this study is to explore the appropriate coupling scale of the coupled atmospheric–hydrologic modeling system, which is established by the Weather Research and Forecasting (WRF) model and the gridded Hebei model with three different sizes (1 km×1 km, 3 km×3 km and 9 km×9 km). The Hebei model is a conceptual rainfall–runoff model designed to describe a mixed runoff generation mechanism, including both storage excess and infiltration excess, in the semi-humid and semi-dry area of northern China. The soil moisture storage capacity and infiltration capacity of different grids in the gridded Hebei model are obtained and dispersed using the topographic index. The lumped Hebei model is also used to establish the lumped atmospheric–hydrologic coupled system as a reference system. Four 24 h storm events occurring at two small- and medium-scale sub-watersheds in northern China are selected as case studies. Contrastive analyses of the flood process simulations from the gridded and lumped systems are carried out. The results show that the flood simulation results may not always be improved with higher-dimension precision and more complicated system, and the grid size selection has a strong relationship with the rainfall evenness. For the storm events with uniform spatial distribution, the coupling scale has less impact on flood simulation results, and the lumped system also performs well. For the storm events with uneven spatiotemporal distribution, the corrected rainfall can improve the simulation results significantly, and higher resolution leads to better flood process simulation. The results can help to establish the appropriate coupled atmospheric–hydrologic modeling system to improve the flood forecasting accuracy.
Highlights
Compared to the traditional flood forecast models that take gauge precipitation as inputs, the coupling of a mesoscale numerical weather prediction (NWP) model with a hydrological model has been proven to be an effective way to improve the accuracy of rainfall–runoff modeling and extend the lead time in real-time flood forecasting (Wu et al, 2014; Wan and Xu, 2011)
The Weather Research And Forecasting (WRF) precipitation forecast with the resolution being 20 km × 20 km was downscaled to 200 m × 200 m, which was suited for the resolution of the hydrological model
The simulation results of the lumped system are close to the gridded system with different grid divisions for storm events 1 and 2, while the simulation results have a significant difference between lumped system and grid system for storm events 3 and 4
Summary
Compared to the traditional flood forecast models that take gauge precipitation as inputs, the coupling of a mesoscale numerical weather prediction (NWP) model with a hydrological model has been proven to be an effective way to improve the accuracy of rainfall–runoff modeling and extend the lead time in real-time flood forecasting (Wu et al, 2014; Wan and Xu, 2011). Most atmospheric–hydrologic coupling studies tend to use lumped or distributed hydrological models (constructed in research watersheds) to run atmospheric models based on hydrological model requirements by inputting meteorological information such as rainfall (Wagner et al, 2016). Liu et al (2015) simulated the floods by a lumped hydrological model integrated with the Weather Research And Forecasting (WRF) model at a 10 km scale at a small catchment (135.2 km). Li et al (2017) extended the flood forecasting lead time in the Liujiang River basin (58 270 km2) by WRF precipitation forecast with a distributed hydrological model. Most studies have no consideration for the spatial-scale matching issue between atmospheric and hydrological models, which has significant impact on the flood forecast accuracy
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