Articles | Volume 18, issue 3
Nat. Hazards Earth Syst. Sci., 18, 765–780, 2018

Special issue: Landslide early warning systems: monitoring systems, rainfall...

Nat. Hazards Earth Syst. Sci., 18, 765–780, 2018

Research article 08 Mar 2018

Research article | 08 Mar 2018

Radar-based quantitative precipitation estimation for the identification of debris flow occurrence over earthquake-affected regions in Sichuan, China

Zhao Shi1,2,3,5, Fangqiang Wei1,2,3, and Venkatachalam Chandrasekar4 Zhao Shi et al.
  • 1Key Laboratory of Mountain Hazards and Earth Surface Process, Chengdu, 610041, China
  • 2Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu, 610041, China
  • 3University of Chinese Academy of Sciences, Beijing, 100049, China
  • 4Department of Electrical and Computer Engineering, Colorado State University, Fort Collins, 80523, USA
  • 5Key Laboratory of Atmospheric Sounding, Chengdu University of Information and Technology, Chengdu 610225, China

Abstract. Both Ms 8.0 Wenchuan earthquake on 12 May 2008 and Ms 7.0 Lushan earthquake on 20 April 2013 occurred in the province of Sichuan, China. In the earthquake-affected mountainous area, a large amount of loose material caused a high occurrence of debris flow during the rainy season. In order to evaluate the rainfall intensity–duration (ID) threshold of the debris flow in the earthquake-affected area, and to fill up the observational gaps caused by the relatively scarce and low-altitude deployment of rain gauges in this area, raw data from two S-band China New Generation Doppler Weather Radar (CINRAD) were captured for six rainfall events that triggered 519 debris flows between 2012 and 2014. Due to the challenges of radar quantitative precipitation estimation (QPE) over mountainous areas, a series of improvement measures are considered: a hybrid scan mode, a vertical reflectivity profile (VPR) correction, a mosaic of reflectivity, a merged rainfall–reflectivity (R − Z) relationship for convective and stratiform rainfall, and rainfall bias adjustment with Kalman filter (KF). For validating rainfall accumulation over complex terrains, the study areas are divided into two kinds of regions by the height threshold of 1.5 km from the ground. Three kinds of radar rainfall estimates are compared with rain gauge measurements. It is observed that the normalized mean bias (NMB) is decreased by 39 % and the fitted linear ratio between radar and rain gauge observation reaches at 0.98. Furthermore, the radar-based ID threshold derived by the frequentist method is I = 10.1D−0.52 and is underestimated by uncorrected raw radar data. In order to verify the impacts on observations due to spatial variation, ID thresholds are identified from the nearest rain gauge observations and radar observations at the rain gauge locations. It is found that both kinds of observations have similar ID thresholds and likewise underestimate ID thresholds due to undershooting at the core of convective rainfall. It is indicated that improvement of spatial resolution and measuring accuracy of radar observation will lead to the improvement of identifying debris flow occurrence, especially for events triggered by the strong small-scale rainfall process in the study area.

Short summary
The aim of this paper is to evaluate the debris flow occurrence thresholds of the rainfall intensity–duration in the earthquake-affected areas of Sichuan province over the rainy seasons from 2012 to 2014. it is clear that radar-based rainfall estimate and threshold supplement the monitoring gap of EWS where rain gauge is scarce. A better understanding of relationship between rainfall and debris flow initiation can be enhanced by the radar with highly spatiotemporal resolution.
Final-revised paper