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Abstract Quantitative horizontal displacement in the landslide potential area is necessary for mitigating casualties, property damage, and economic loss. Focusing on a sliding within a deep-seated landslide potential area located in Guanghua area in northern Taiwan, this study employed an unmanned aerial system (UAS) to capture and produce seven high-precision orthomosaics from February 23 to March 26, 2021. Through particle image velocimetry (PIV) method, these orthomosaics were used to assess the two-dimensional land surface displacement in the sliding-movement region. The results revealed substantial displacement in the study region within the monitoring period. The direction of displacement was consistent with the slope aspect in the region. To evaluate the suitability of the proposed model, the coefficient of efficiency was chosen to determine the goodness-of-fit between the observed and calculated two-dimensional displacement in situ land surface displacement extensometer. The result showed that coefficient of efficiency was up to 0.998. In addition, the greatest displacement was observed in the vegetated section located at the bottom of the sliding-movement region. This section also had the highest slope, and its maximum tree-crow displacement exceeded 9 m. PIV facilitated easy identification of the range and boundaries of the sliding area. This noncontact monitoring technique overcame the limitations of single-point displacement assessment, obviating the time-consuming, costly processes involved in conventional monitoring methods. The achieved results obtained by proposed method gave a worthy support for an accurate understanding and evaluation of the landslide processes in the watershed. The technique can also be applied to other critical infrastructure sites, allowing hazard risk reduction.

The ocean surface waves during Super Typhoons Maria (2018), Lekima (2019), and Meranti (2016) were reproduced using hybrid typhoon winds and a fully coupled wave-tide-circulation modeling system (SCHISM-WWM-III). The hindcasted significant wave heights are in good agreement with the along-track significant wave heights measured by the altimeters aboard the SARAL (Satellite with ARgos and ALtiKa) and Jason-2 satellites. Two numerical experiments pairing Super Typhoons Maria (2018) and Meranti (2016) and Super Typhoons Lekima (2019) and Meranti (2016) were conducted to analyze the storm wave characteristics of binary and individual typhoons. Four points located near the tracks of the three super typhoons were selected to elucidate the effects of binary typhoons on ocean surface waves. The comparisons indicate that binary typhoons not only cause an increase in the significant wave height simulations at four selected pints but also result in increases in the one-dimensional wave energy and two-dimensional directional wave spectra. Our results also reveal that the effects of binary typhoons on ocean surface waves are more significant at the periphery of the typhoon than near the center of the typhoon. The interactions between waves generated by Super Typhoons Maria (2018) and Meranti (2016) or Super Typhoons Lekima (2019) and Meranti (2016) might be diminished by Taiwan Island even if the separation distance between two typhoons is

Landslide-generated seismic waves (landslide-quakes), exhibiting distinctive waveforms and frequency characteristics, can be recorded by nearby seismometers. Implementing an automatic classifier for landslide-quakes could help provide objective and accurate initiation times of landslides with efficiency. This study collected and analyzed the time information of 214 landslide seismic records due to 33 documented landslide events, from the Broadband Array in Taiwan for Seismology (BATS). In addition, equal numbers of earthquake and noise signals were also incorporated. The 642 seismic signals and time information were carefully examined using the random forest algorithm to create an automatic landslide-quake classifier. By validating the signal attributes of the landslide, earthquake, and noise events, specifically in the time and frequency domains, it was shown that the proposed classifier can reach an accuracy (the proportion of all correctly classified events to the total number of events) of 91.3%. To further evaluate the applicability of the automatic classifier, landslide-quakes generated during the devastating Typhoon Morakot (2009) and Typhoon Soudelor (2015) were also verified, showing that the sensitivity of the classifier is higher than 98%.

Fluctuations in the sediment yielding rate within mountainous areas are found after extreme precipitations. These changes are associated with rainfall-driven landslides and can be evaluated through observations of sediment transported in river water. In this study, we assess the differential impact level and duration of an extreme rainfall event caused by the 2009 Typhoon Morakot in Taiwan. Using a time series of suspended sediment data and landslide inventories within three affected catchments, our results found that the proportion of the typhoon-generated sediment discharges reached 58% of the 2009 annual sediment discharges, and the annual sediment discharges could be 15-fold higher than the average annual sediment discharges prior to the typhoon. The impact of the typhoon on suspended sediment discharge lasted for around four months. It is further revealed that a significant increase in the number of landslides was attributed to the impact of the extreme typhoon event, and the critical rainfall condition triggering landslides, based on the relationship between rainfall and landslide number and the rainfall intensity-duration thresholds, declined for 4–5 years.

Super Typhoon Nepartak (2016) was used for this case study because it is the most intense typhoon that made landfall in Taiwan in the past decade. Winds extracted from the Climate Forecast System version 2 (CFSV2) and ERA5 datasets and merged with a parametric typhoon model using two hybrid techniques served as the meteorological conditions for driving a coupled wave-circulation model. The computed significant wave heights were compared with the observations recorded at three wave buoys in the eastern waters of Taiwan. Model performance in terms of significant wave height was also investigated by employing the CFSV2 winds under varying spatial and temporal resolutions. The results of the numerical experiments reveal that the simulated storm wave heights tended to decrease significantly due to the lower spatial resolution of the hourly winds from the CFSV2 dataset; however, the variations in the storm wave height simulations were less sensitive to the temporal resolution of the wind field. Introducing the combination of the CFSV2 and the parametric typhoon winds greatly improved the storm wave simulations, and similar phenomena can be found in the exploitation of the ERA5 dataset blended into the parametric wind field. The overall performance of the hybrid winds derived from ERA5 was better than that from the CFSV2, especially in the outer region of Super Typhoon Nepartak (2016).

Typhoon-induced storm surges are catastrophic disasters in coastal areas worldwide, although typhoon surges are not extremely high in Taiwan. However, the rising water level around an estuary could be a block that obstructs the flow of water away from the estuary and indirectly forms an overflow in the middle or lower reaches of a river if the occurrence of the highest storm surge (HSS) coincides with the highest astronomical tide (HAT). Therefore, assessing the highest storm tide (HST, a combination of the HSS and HAT) hazard level along the coast of Taiwan is particularly important to an early warning of riverine inundation. This study hindcasted the storm surges of 122 historical typhoon events from 1979 to 2018 using a high-resolution, unstructured-grid, surge-wave fully coupled model and a hybrid typhoon wind model. The long-term recording measurements at 28 tide-measuring stations around Taiwan were used to analyze the HAT characteristics. The hindcasted HSSs of each typhoon category (the Central Weather Bureau of Taiwan classified typhoon events into nine categories according to the typhoon’s track) were extracted and superposed on the HATs to produce the individual potential HST hazard maps. Each map was classified into six hazard levels (I to VI). Finally, a comprehensive potential HST hazard map was created based on the superposition of the HSSs from 122 typhoon events and HATs.

The tidal current power (TCP) resource, the impact of TCP extraction on hydrodynamics and the influence of sea-level rise (SLR) on TCP output in the coastal waters of Kinmen Island (Taiwan) are investigated using a state-of-the-art unstructured-grid depth-integrated numerical model. The model was driven by eight tidal constituents extracted from a global tidal prediction model and verified with time series of measured data for tide level and depth-averaged current. The simulations showed reasonable agreement with the observations; the skill index was in the excellent (0.71–0.93) range with regard to simulating tide level and currents. Model predictions indicated that the channel between Kinmen and Lieyu serves as an appropriate site for deploying the tidal turbines because of its higher tidal current and deeper water depth. The bottom friction approach was utilized to compute the average TCP over a spring-neap cycle (i.e., 15 days). Mean TCP reached its maximum to 45.51 kW for a coverage area of 0.036 km2 when an additional turbine friction coefficient (Ct) increased to 0.08, and a cut-in speed of 0.5 m/s was used. The annual TCP output was estimated to be 1.08 MW. The impact of TCP extraction on the change in current is significant, with a maximum reduction rate of instant current exceeding 60%, and the extent of influence for the average current is 1.26 km in length and 0.30 km in width for the −0.05 m/s contour line. However, the impact of TCP extraction on the change in tide level is insignificant; the maximum change in amplitude is only 0.73 cm for the K2 tide. The influence of SLR on the TCP output in Kinmen waters was also estimated. Modeling assessments showed that due to SLR produces faster tidal current, the annual TCP output increased to 1.52 MW, 2.01 MW, 2.48 MW and 2.97 MW under the same cut-in speed and coverage area conditions when SLR 0.25 m, SLR 0.5 m, SLR 0.75 m and SLR 1.0 m were imposed on the model.

The given document is an editorial for a special issue of the Journal of Disaster Research. The special issue focuses on the Integrated Research on Disaster Risk (IRDR) program in Taipei, Taiwan. The IRDR ICoE Taipei is a research program for disaster risk reduction, co-sponsored by the International Science Council and the United Nations Office for Disaster Risk Reduction. The special issue includes a review of the program's capacity building efforts and three research articles on topics such as ecosystem-based disaster risk reduction, sustainable rice economics, and soil wall reinforcement. This special issue is the first collaboration between IRDR ICoE Taipei and the Journal of Disaster Research, with support from the National Science and Technology Center for Disaster Reduction and Academia Sinica of Taiwan. [Extracted from the article]

One of the purposes of slope disaster research is to establish an early warning method for rainfall-induced landslides. The insufficient observational records of the past, however, have inhibited the analysis of critical rainfall conditions. This dilemma may be resolved by extracting the times of landslide occurrences from the seismic signals recorded by adjacent seismic stations. In this study, the seismic records of the Broadband Array in Taiwan for Seismology (BATS) were examined to identify the ground motion triggered by large-scale landslides occurring from 2005 to 2014. After the signals from local and teleseismic earthquakes were eliminated, 62 landslide-induced seismic signals were identified. The seismic signals provided the occurrence times of the landslides for assessment of the rainfall conditions, including rainfall intensity (I, mm/h), duration (D, h), and cumulated rainfall (R, mm). Comparison of three common rainfall threshold models (I-D, I-R, and R-D) revealed duration and cumulated rainfall to be the crucial factors in developing a forecast warning model. In addition, a critical volume of water model, (I - 1.04) x D = 452 mm, combining statistical and deterministic approaches was established through analysis of rainfall information from the 62 large-scale landslides that occurred. [ABSTRACT FROM AUTHOR]

The article provides information on the effects of earthquake and cyclone sequencing on landsliding and fluvial sediment transfer in a mountain catchment. It is stated that strength, location, and sequencing of rain storms and earthquakes are the key determinants in identifying the patterns and rates of landsliding and fluvial sediment transfer. To be able to explore the scenario, mapping of landslides caused by three tropical cyclones and a very large earthquake in the Chenyoulan catchment in Taiwan Central Range has been done. Water and sediment discharges and rock strengths are also discussed to expound on the topic.

The paper reports on a study of the weak sandstones of the Shihti and Kweichulin Formations to the east of Taipei, Taiwan. The results indicate that the wave velocity and uniaxial compressive strength (UCS) of the samples decreased as water content increased, while wave velocity, UCS and slake durability increased with increasing porosity. Regression analyses demonstrated that wave velocity, UCS and slake durability decreased with increased quartz content. The values of these engineering properties also increased with a higher proportion of matrix/detritus, although the exact nature of the interrelationships between these factors is not clear. [ABSTRACT FROM AUTHOR]

By means of an onsite investigation, the largest debris flow in Taiwan's history is analyzed in this paper. A heavy rainfall of 1,748 mm/day occurred during typhoon Herb in the Hoser area at the end of July 1996. Aerial photographic assessment and observations of geological and geomorphological features have contributed to our understanding of this massive destruction. Mechanisms of the hazardous debris flow are explored and discussed. Data revealed that the rock discontinuities were a major factor in the voluminous loose materials in the debris flows. The heavy and rapid rainfall instantly transported massive amounts of debris flow materials into the center, and then quickly funneled them to the lower parts of gullies. The heavy slurry became an effective cutting device to erode the side walls and move large quantities of the debris materials to the end of the gullies. [ABSTRACT FROM AUTHOR]

In tectonically active mountain belts, earthquake-triggered landslides deliver large amounts of sediment to rivers. We quantify the geomorphic impact of the 1999 Mw 7.6 Chi-Chi earthquake in Taiwan, which triggered >20,000 landslides. Coseismic weakening of substrate material caused increased landsliding during subsequent typhoons. Most coseismic landslides remained confined to hillslopes. Downslope transport of sediment into the channel network occurred during later storms. The sequential processes have led to a factor-of-four increase in unit sediment concentration in rivers draining the epicentral area and increased the magnitude and frequency of hyperpycnal sediment delivery to the ocean. Four years after the earthquake, rates of hillslope mass wasting remain elevated in the epicentral area. [ABSTRACT FROM AUTHOR]

Climate controls landscape evolution, but quantitative signatures of climatic drivers have yet to be found in topography on a broad scale. Here we describe how a topographic signature of typhoon rainfall is recorded in the meandering of incising mountain rivers in the western North Pacific. Spatially averaged river sinuosity generated from digital elevation data peaks in the typhoon-dominated subtropics, where extreme rainfall and flood events are common, and decreases toward the equatorial tropics and mid-latitudes, where such extremes are rare. Once climatic trends are removed, the primary control on sinuosity is rock weakness. Our results indicate that the weakness of bedrock channel walls and their weakening by heavy rainfall together modulate rates of meander propagation and sinuosity development in incising rivers. [ABSTRACT FROM AUTHOR]