## 7 Conclusions  
A conclusion can be drawn based on the comprehensive results of the observed data from ten stations: regardless of the effect of the base flow on the areal strain, the rainfall will have a different impact on the RQR based on the geological and topographic differences of the surrounding areas of the stations. The rainwater that is not able to infiltrate into the ground immediately after falling merges with the land-surface runoff and induce the quick response of strainmeter. It demonstrates the maximum response in a short period of time due to the impact of the cumulative weight of the water and then exponentially decreased as rainwater flowed out of the range. The fluctuations of topography will affect the rainfall decay time, whereas the river beside might help accelerating runoff dispersion. The larger cumulative rainfall will have a stronger effect on rock flow-sensitive areas. When the cumulative rainfall reached a specific threshold in such an area, the whole area likely experienced a rainfall-induced landslide or debris flow. The responding strain curve potentially shows abnormal under the domination of landslide events.  
In the long term, the strain trend will be affected by groundwater flow, but this process will range from 1 to 7 days, which was longer than surface runoff (Table 2). At present, we only scoped on the impact of surface overload on deformation observations in this study, and did not yet consider the effects of groundwater. To understand the whole proceeding of rainwater's influence on and under the ground, it is required to involve in the studies of underground hydrology and hydrodynamics. That will be important for our future research.  
On the other hands, the observed results implied that the noise level will be increasing if a borehole strainmeter station settled by the river due to river hydrology and landslides. More effort will be required to reduce the noise level to acquire accurate observation results. Therefore, building a station in such an environment is not advisable. However, stations by the river courses are sometimes unavoidable for crustal strain observations due to the elevated terrain at the fold-and-thrust belt in ongoing mountain building of Taiwan orogenic belt. For the stations vulnerable to the impact of river flow variation, more careful considerations are required with respect to data processing and interpretation.  
The following are available online at [[https://www.mdpi.com/2076-341](https://www.mdpi.com/2076-341)]([https://www.mdpi.com/2076-341](https://www.mdpi.com/2076-341)) 7/11/3/1301/s1. Figure S1: The diagrams show the relief maps of the vicinity of borehole strainmeter stations. Figure S2: diagram of rainfall impact function. Figure S3: The diagram shows the relation of a specific underground point, P and a strip load with width of B past aside on the ground. Figure S4: The photo was taken on the riverside by the DARB.  
Conceptualization, C.-Y.C. ([PERSON]) and J.-C.-H.; data curation, C.-Y.C. ([PERSON]) and C.-Y.C. ([PERSON]); formal analysis, C.-Y.C. ([PERSON]); methodology, C.-Y.C. ([PERSON]), J.-C.H. and C.-C.L.; resources, C.-Y.C. ([PERSON]); software, C.-Y.C. ([PERSON]), C.-C.L. and C.-Y.C. ([PERSON]); supervision, J.-C.H.; writing--original draft, C.-Y.C. ([PERSON]); writing--review & editing, J.-C.H. and C.-C.L. All authors have read and agreed to the published version of the manuscript.  
This research was partially supported by National Taiwan University and Ministry of Science and Technology, Taiwan, under the grants MOST 105-2116-M-002-003 and project of Central Geological Survey under the grant 105-5226904000-01-01.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
We thank the constructional comments from assistant editor [PERSON] and 3 anonymous reviewers to largely improve the manuscript. We benefit from fruitful discussions with [PERSON] and [PERSON]. We thank the Central Geological Survey for providing the borehole strainmeter data.