Abstract
This study investigates the geological background of the August 7-8, 2010 Zhouqu debris flows in the northwestern Chinese province of Gansu, and possible future occurrence of such hazards in the peri-Tibetan Plateau (TP) regions. Debris flows are a more predictable type of landslide because of its strong correlation with extreme precipitation. However, two factors affecting the frequency and magnitude of debris flows: very fine scale precipitation and degree of fracture of bedrock, both defy direct observations. Annual mean Net Primary production (NPP) is used as a surrogate for regional precipitation with patchiness filtered out, and gravity satellite measured regional mass changes as an indication of bedrock cracking, through the groundwater as the nexus. The GRACE measurements indicate a region (to the north east of TP) of persistent mass gain (started well before the 2008 Wenchuan earthquake), likely due to increased groundwater percolation. While in the neighboring agricultural region further to the north east, there are signal of decreased fossil water reservoir. The imposed stress fields by large scale increase/decrease groundwater may contribute to future geological instability of this region. Zhouqu locates right on the saddle of the gravity field anomaly. The region surrounding the Bay of Bangle (to the southeast of TP) has a similar situation. To investigate future changes in extreme precipitation, the other key player for debris flows, the “pseudo-climate change” experiments of a weather model forced by climate model provided perturbations on the thermal fields are performed and endangered locations are identified. In the future warmer climate, extreme precipitation will be more severe and debris will be more frequent and severe.
Highlights
On August 8, 2010 in the northwestern Chinese province of Gansu, more than 1000 people died when a debris flow devastated the small county of Zhouqu
Initial and lateral boundary conditions were based on Global Forecast System (GFS) final analyses on a 1 degree latitude-longitude grid; simulations were initialized at 00 UTC 04 August 2010 run for 6 days
Surrounding the Tibetan Plateau (TP), there are a train of regions suffering steady mass gain in the past decade
Summary
On August 8, 2010 in the northwestern Chinese province of Gansu, more than 1000 people died when a debris flow devastated the small county of Zhouqu. The future occurrence frequency of this type of landslides is an immediate practical concern for mountainous regions. Landslides are partly an upscale process, with localized disturbances adding instability, by adding fluids or reducing root reinforcement [1], to pre-existing weathered regolith and granular soil particles spreading on slopes in a region predisposed to geo-hazards. The background of the Zhouqu landslides (Figure 1) is addressed. The geological and hydrological circumstances of this event are examined. Remote sensing observations over the past decade provide an opportunity to examine the bedrock cracking conditions over the peripheral Himalayan region, which includes both Zhouqu County and the 2008 Wenchuan earthquake affected areas
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