## 4 Conclusions  
An early warning system of MEMS based multi-source wireless monitoring for rainfall-induced landslides is proposed. This system was tested and established on a real landslide-prone slope in the Wenchuan earthquake region, China, and long-term monitoring data was observed.  
(1) The proposed real-time monitoring system is composed of low-cost and portable wireless sensor units, which, when integrated with a MEMS based inclinometer, tensiometer, rainfall gauge and soil moisture sensor, renders the system capable of measuring multi-source parameters corresponding  
Figure 10: Correlation of slope stability and soil moisture content, matric suction and daily rainfall, plotting by the stability analysis. Modeled factor of safety versus (**a**) observed volumetric water content, (**b**) observed suction and (**c**) observed daily rainfall which indicates the water contents and suction thresholds models for early warning of the mass-remobilization in the Yindongzi landslide site in hollows of debris flows of the Wenchuan earthquake region.  
to rainfall-induced landslides. The sensor unit features ultralow power consumption so as to be easy-to-maintain for landslide monitoring.  
(2) The long-term fluctuations in the soil moisture content, matric suction, and rainfall were observed and slope stability in response to rainfall infiltration was simulated. The corresponding slope failures during a rainy period could have been were observed by ground vibration, indicating that the reduction in matric suction and the rise in soil moisture in response to rainfall infiltration contributes enormously to slope stability of rainfall-triggered landslides, especially in terms of shallow mass movement.  
(3) Based on instrumental field observations and the quantitative slope stability analysis for an unsaturated slope, a method to determine multi-source thresholds of hydrological parameters, including daily rainfall intensity, soil moisture content and matric suction, for use as early warning criteria for rainfall-induced landslides in the Wenchuan earthquake region was proposed.  
The proposed explorations indicate that field measurements and a threshold model including precipitation, soil wetness, and pore pressure (soil suction) are significant in identifying states under which rainfall-induced landslides are likely to initiate. The proposed low-cost and effective early warning method combined with a multi-parameter threshold for anticipating rainfall-induced landslide activity provide powerful tools to conduct a landslide early warning system that could be adopted to reduce landslide risk.  
This work was financially supported by the National Natural Science Foundation of China (Grant No. 41771021, 41471012) and the Hundred Young Talents and 135 Strategic Program of IMHE (Grant No. SDSQB-2016-01, SDS-135-1701, SDS-135-1704), and Science and Technology Service Network Initiative of Chinese Academy of Science (Grant No. KFJ-EW-STS-094, KFJ-STS-ZDTP-015). The Field Observation and Research Base of Geological Hazards in Chengdu Earthquake Disturbed Area of Longmen Mountain, Ministry of Land and Resources of China provided some data for this work.  
[PERSON] and [PERSON] conceived and designed the early warning system; [PERSON], [PERSON], [PERSON], and [PERSON] established and performed the early warning system; [PERSON] and [PERSON] contributed analysis tools; [PERSON] wrote the paper.  
The authors declare no conflict of interest.