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This study describes the use of inventory-based landslide susceptibility index (LSI) models based on the selection of causative factors, functional relationships between factors and integration to a hazard-warning model. We first merged landslide inventory data of five typhoon-training events and obtained sets of data representing environmental conditions where landslides are likely to occur. These well-defined data sets are used to select five representative causative factors, i.e. the slope angle, rock strength, drainage, curvature and soil type. Four bivariate statistical model combinations were tested: the linear combination, geometric mean, and two other mixed combinations. As a result, the modulation effects between (i) rock strength and slope and (ii) drainage and curvature were intensified in mixed model 2 (MX2) through factor multiplication. The MX2 LSI was integrated with three multivariate landslide hazard-warning models and tested with four triggering factor rainfall parameter sets. Results lead to the conclusion that threshold models with terrain-influenced rainfall can better identify hazard-warning locations. Modulating factor combinations for the hazard warning can also mirror true environmental conditions, yielding more representative model results. This study improves the method for identifying LSI models for the application to rainfall-triggered landslide hazard models. [ABSTRACT FROM AUTHOR]

This study investigated the streamflow impacts in wet and dry spells using a statistical downscaling projection method to obtain 5 km girds under four Representative Concentration Pathway (RCP) scenarios. Two upstream catchments, the Dahan and Laonong Rivers were selected as the study areas. A water balance hydrological model, also known as the Generalized Watershed Loading Function model, was used to simulate the streamflow impacts. There are 126 projections from 41 general circulation models (GCMs) and 4 RCPs used in this analysis. The analytical results indicate that the streamflow impacts in different RCP scenarios are significant but vary with individual GCM's projection. The variance of 20 selected GCMs is close to that of all other GCMs. Typically, more than 60% of GCMs project that in the early 21st century, streamflow in each RCP increases by 0 - 40% in wet spells and decrease by -40 ~ 0% for the Dahan River, but the streamflow increases during both wet and dry spells for the Laonong River. In the late 21st century, the streamflow decreases by 60% during dry spells in the Laonong River. Various predictions for the early and late 21st century show high variance of streamflow impacts. As such, decision makers must plan for reservoir operation and flexible water deployment adaptations during future dry spells. [ABSTRACT FROM AUTHOR]

'Disaster risk assessment' is important in the planning of risk management strategies that reduce societal losses. However, governmental agencies in Taiwan generally assess risks that emerge from debris flows without adequately considering risk management and taking a systems approach. This work proposes an approach to thoroughly consider the interactive influence mechanism of debris flow disaster risk. Additionally, a systematic method for assessing disaster risks is developed. This proposed method can be used in the current risk assessment and as a basis for management strategy planning. Based on systems thinking, the components and attributes of a conceptual system of disaster risk management associated with debris flows in a river basin are identified. Subsequently, a conceptual mitigation-hazard-exposure-resistance framework and an indicator system for assessing the debris flow disaster risks in a river basin are identified. The disaster risks for each exposed community in each drainage zone can be systematically calculated based on the current status or plans of prevention and evacuation measures using the proposed indicator system. A case study of implementing the proposed methodology that involves the Chishan River Basin is presented, in which disaster risk according to the current status of prevention and evacuation measures is assessed. Drainage zones and communities with a significant debris flow disaster risk are located; this risk is associated with a lack of adequate prevention and evacuation measures that have been planned of government agencies. Analytical results indicate that the proposed methodology can systematically and effectively assess the disaster risks of a river basin. The proposed methodology provides a valuable reference for governmental agencies that must manage disaster risk associated with debris flows. [ABSTRACT FROM AUTHOR]

Landslides have been identified as one of the costliest and deadliest natural disasters, causing tremendous damage to humans and societies. Information regarding the spatial extent of landslides is thus important to allow officials to devise successful strategies to mitigate landslide hazards. This study aims to develop a machine-learning approach for predicting landslide areas in the Tsengwen River Watershed (TRW), which is one of the most landslide-prone areas in Central Taiwan. Various spatial datasets were collected from 2009 to 2015 to derive 36 predictive variables used for landslide modeling with random forests (RF). The results of landslide prediction, compared with ground reference data, indicated an overall accuracy of 91.4% and Kappa coefficient of 0.83, respectively. The findings achieved from estimates of predictor importance also indicated to officials that the land-use/land-cover (LULC) type, distance to previous landslides, distance to roads, bank erosion, annual groundwater recharge, geological line density, aspect, and slope are the most influential factors that trigger landslides in the study region. [ABSTRACT FROM AUTHOR]

The Zhe-Min mountainous rivers in SE China are characterized by stable tectonics, small–mesoscale drainage basins, relatively homogenous bedrocks, dense vegetation cover and high rainfall conditions. These rivers deliver loads of sediments and nutrients to the oceans and always indicate considerably high variability of sediment flux on short-term timescales. However, short-term sediment compositional variations and transport mechanism by these mountainous rivers remain poorly understood. Here we target the Minjiang River, use mineralogical and trace element geochemical data of suspended particulate matters (SPMs) within a one-year hydrological cycle (from October 2016 to October 2017), riverbed sediments (<0.063 mm fractions) and SPMs from the mainstream and major tributaries, to investigate their provenance and transport process. The results indicate that the SPMs in different seasons have strong seasonal geochemical heterogeneity, with highly positive correlations between several trace element ratios (e.g. La (CN) /Yb (CN) and Th/Sc) and runoff of the river. Riverbed sediments and SPMs collected in pairs have distinct geochemical compositions. The riverbed sediments have relatively low La (CN) /Yb (CN) (ca. 10–15) and Th/Sc (ca. 2–5) ratios, whereas the SPMs have La (CN) /Yb (CN) and Th/Sc ratio ranges of ca. 14–17 and ca. 4–7, respectively. These findings suggest a predominant hydrologic control on the Minjiang River sediment transport and geochemical compositions on a seasonal timescale. We conclude that exposed riverbed sediments are probably selectively recycled in dry-season sediment transport, whereas the flood-season SPMs are less mixed with riverbed sediments and are likely dominated by particulates directly from those tributaries and the upper mainstream. We favor that the Zhe-Min mountainous rivers are featured by rapid sediment delivery in response to hydroclimatic changes and have similar sediment transport behaviors with those small mountainous rivers in tectonically active regions of the subtropical East Asia (e.g. Taiwan). This case study also highlights the importance of multi-spatio-temporal scale, heterogeneous river input of chemical elements to the oceans. • Minjiang River sediments are investigated for mineralogy and geochemistry. • Riverbed sediments and SPMs in pairs have distinct geochemical compositions. • La/Yb and Th/Sc ratios of SPMs correlate positively with the river runoff. • Riverbed and overbank sediments are selectively recycled in dry season transport. • The river shows a hydrologic control on sediment geochemical compositions. [ABSTRACT FROM AUTHOR]