Papers by Kang-tsung Chang
Habitat International, 2016
Geomorphology, 2015
ABSTRACT This study calculated the long-term average landslide erosion rate in the Kaoping River ... more ABSTRACT This study calculated the long-term average landslide erosion rate in the Kaoping River watershed in southern Taiwan and investigated the relative importance of extreme rainfall events on landslide erosion. The method followed three steps: first, calculating landslide volumes for 10 rainfall events from a multi-temporal, event-based landslide inventory; second, estimating the frequency of landslide-generating rainfall by using hydrologic frequency analyses; and third, combining the two sets of data to estimate the average landslide erosion rate. Results of the study showed that the average landslide erosion rate is 2.65–5.17 mm yr− 1, corresponding well to rates reported in other studies using other methods. The study also found that extreme-intensive rainfall events play a more important role on landslide erosion than frequent-moderate rainfall events. Extreme rainfall (maximum 24-h rainfall > 600 mm) contributes 64–79% of the average landslide erosion rate. Moreover, the natural variation of landslide erosion magnitudes is extremely large and can cause significant uncertainty in estimating the landslide erosion rate from total landslide volume. This study found ± 1.2 mm yr− 1 of uncertainty based on simulation results involving a hypothetical 100-year landslide inventory. In summary, this study demonstrates the importance of extreme rainfall events on landslide erosion, and the method proposed in this study is capable of calculating a reliable estimate of average landslide erosion rate in areas with insufficient landslide records.
The Professional Geographer, 2006
This article analyzes spatial and temporal changes of aquaculture land use in Yunlin County, Taiw... more This article analyzes spatial and temporal changes of aquaculture land use in Yunlin County, Taiwan, and discusses the driving forces for these changes. Digital land-use maps and satellite imagery for 1982, 1988, 1994, and 2002 were used to extract aquaculture areas. A geographic information system was used to derive changes in aquaculture areas and to compute the spatial clustering statistics over time. A survey of eighty-seven farmers was conducted to obtain their views and concerns about aquaculture. The results show a rapid expansion in aquaculture during the 1980s, driven mainly by exports to Japan, and a continuous decline since the mid-1990s because of economic, environmental, and demographic factors.
Natural Hazards and Earth System Science, 2011
We developed a multi-scale OBIA (object-based image analysis) landslide detection technique to ma... more We developed a multi-scale OBIA (object-based image analysis) landslide detection technique to map shallow landslides in the Baichi watershed, Taiwan, after the 2004 Typhoon Aere event. Our semi-automated detection method selected multiple scales through landslide size statistics analysis for successive classification rounds. The detection performance achieved a modified success rate (MSR) of 86.5 % with the training dataset and 86 % with the validation dataset. This performance level was due to the multi-scale aspect of our methodology, as the MSR for single scale classification was substantially lower, even after spectral difference segmentation, with a maximum of 74 %. Our multi-scale technique was capable of detecting landslides of varying sizes, including very small landslides, up to 95 m 2 . The method presented certain limitations: the thresholds we established for classification were specific to the study area, to the landslide type in the study area, and to the spectral characteristics of the satellite image. Because updating site-specific and image-specific classification thresholds is easy with OBIA software, our multi-scale technique is expected to be useful for mapping shallow landslides at watershed level.
International Journal of Geographical Information Science, 2000
Snow courses that measure snow water equivalent (SWE) are clustered and limited in areal coverage... more Snow courses that measure snow water equivalent (SWE) are clustered and limited in areal coverage in Idaho. This study used a cell-based geographic information system and multiple regression models to construct SWE surfaces from the snow course data by month (January to May) and by watershed. SWE was the dependent variable and location and topographic variables derived from a digital elevation model were used as the independent variables. Multiple regression performed better than the traditional interpolation methods for SWE estimation. The estimated SWE surface can be displayed at diOE erent spatial scales through neighbourhood operations, or used directly as a map layer for hydrologic modelling.
Calibration of landscape evolution models (LEMs) needs long term input data on climate and soil r... more Calibration of landscape evolution models (LEMs) needs long term input data on climate and soil redistribution. Rainfall data over the last decades can often be estimated from field stations and interpolation. A decadal estimate of soil redistribution can be derived from analysing the spatial variation of the Caesium-137 inventory in the soil. The objective of this case study is to
The recent modification of the Water Erosion Prediction Project (WEPP) model has improved its app... more The recent modification of the Water Erosion Prediction Project (WEPP) model has improved its applicability to hydrology and erosion modeling in forest watersheds. To generate reliable topographic and hydrologic inputs for the WEPP model, carefully selecting digital elevation models (DEMs) with appropriate resolution and accuracy is essential because topography is a major factor controlling water erosion. Light detection and ranging (LIDAR) provides an alternative technology to photogrammetry for generating fine-resolution and high-quality DEMs. In this study, WEPP (v2006.201) was applied to hydrological and erosion simulation for two small forest watersheds in northern Idaho. Data on stream flow and total suspended solids (TSS) in these watersheds were collected and processed. A total of six DEMs from the National Elevation Dataset (NED), Shuttle Radar Topography Mission (SRTM), and LIDAR at three resolutions (30 m, 10 m, and 4Ăm) were obtained and used to calculate topographic parameters as inputs to the WEPP model. WEPP-simulated hydrologic and erosion results using the six DEMs were contrasted and then compared with field observations. For the study watersheds, DEMs with different resolutions and sources generated varied topographic and hydrologic attributes, which in turn led to significantly different erosion simulations. WEPP v2006.201 using the 10 m LIDAR DEM (vs. using other DEMs) produced a total amount of as well as seasonal patterns of watershed discharge and sediment yield that were closest to field observations. xcessive sedimentation in forest streams is one of the main concerns in forest management and water quality control . There is a need to adequately simulate and predict sedimentation from hillslopes to streams at the watershed scale in forested areas. However, simulation results can be greatly influenced by the topographic and hydrologic inputs . Numerous studies have shown that the reliability of the derived topographic and hydrologic attributes depends on the resolution and accuracy of the input digital elevation model (DEM), a common format for representing topography digitally (Jenson and Domingue
Habitat International, 2015
ABSTRACT With its phenomenal development in recent decades, urbanization in China has been covere... more ABSTRACT With its phenomenal development in recent decades, urbanization in China has been covered in a large number of studies. These studies have focused on large cities, with smaller and lesser known cities largely overlooked. This study analyzed the spatiotemporal changes of land use in Quanzhou, a historical city in Fujian Province, using GIS and remote sensing tools. Based on the land use change indices and spatial metrics, our results showed that built-up (urban) land in Quanzhou increased more than twofold in 1995–2010, at the expense of cultivated land, woodland, and grassland. During the same period, urban land patches increased in both number and size, while becoming more irregular and complex in shape. Most urban land expansion took place in the coastal areas, including the city districts and development and industrial zones. Although urbanization in Quanzhou has been remarkable since 1995, its average rate of urban land expansion has fallen behind Shenzhen and Dongguan in the Pearl River Delta. Geographic location and population growth are two important factors for the difference. Quanzhou is located in a less developed region of China, and its population growth has been slow due to its heavy reliance on labor-intensive, low-technology industries, which do not offer sufficient rural—urban wage differential to attract large inflows of migrant workers. Urbanization in China follows different paths in different cities and regions, as shown in this study by comparing Quanzhou with cities in the Pearl River Delta.
ABSTRACT This study proposes a new shallow landslide model, integrating a size-explicit landslide... more ABSTRACT This study proposes a new shallow landslide model, integrating a size-explicit landslide prediction model, an event-based transient soil moisture model, and a debris flow model. The model is expected to predict the location, timing, size, and landslide runout for a rainfall-induced landslide. In the study, we first examined a coupled model to simulate, at watershed level, landslides and debris flows induced by Typhoon Morakot (August, 2009) in southern Taiwan. Although the coupled model performed reasonably well in model test and validation, it overestimated unstable areas (cells) and underestimated debris fluxes downslope. The problems are most likely due to the landslide model, SHALSTAB, used in the coupled model, which is hydrologically steady-state and size-inexplicit. To solve the problems, we will implement a new landslide model, capable of predicting the hydrology dynamics and landslide size. The new integrated model will be tested with past event data in the Baichi catchment in northern Taiwan and the Coos Bay watershed in northwestern United States. The landslide triggers are different in these two study areas: mid-latitude cyclones that affect Coos Bay are much milder rainfall events than typhoons that affect Baichi. A comparative analysis between these two study areas will also offer an opportunity to examine the controls of rainfall pattern, topography, land cover, and soil physics on landsliding and landslide size. Keywords: shallow landslide, soil moisture, debris flow, landslide size, typhoon
The vast availability and improved quality of optical satellite data and digital elevation models... more The vast availability and improved quality of optical satellite data and digital elevation models (DEMs), as well as the need for complete and up-to-date landslide inventories at various spatial scales have fostered the development of semi-automated landslide recognition systems. Among the tested approaches for designing such systems, object-based image analysis (OBIA) stepped out to be a highly promising methodology. OBIA offers a flexible, spatially enabled framework for effective landslide mapping. Most object-based landslide mapping systems, however, have been tailored to specific, mainly small-scale study areas or even to single landslides only. Even though reported mapping accuracies tend to be higher than for pixelbased approaches, accuracy values are still relatively low and depend on the particular study. There is still room to improve the applicability and objectivity of object-based landslide mapping systems. The presented study aims at developing a knowledge-based landslide mapping system implemented in an OBIA environment, i.e. Trimble eCognition. In comparison to previous knowledge-based approaches, the classification of segmentation-derived multi-scale image objects relies on digital landslide signatures. These signatures hold the common operational knowledge on digital landslide mapping, as reported by 25 Taiwanese landslide experts during personal semi-structured interviews. Specifically, the signatures include information on commonly used data layers, spectral and spatial features, and feature thresholds. The signatures guide the selection and implementation of mapping rules that were finally encoded in Cognition Network Language (CNL). Multi-scale image segmentation is optimized by using the improved Estimation of Scale Parameter (ESP) tool. The approach described above is developed and tested for mapping landslides in a sub-region of the Baichi catchment in Northern Taiwan based on SPOT imagery and a high-resolution DEM. An object-based accuracy assessment is conducted by quantitatively comparing extracted landslide objects with landslide polygons that were visually interpreted by local experts. The applicability and transferability of the mapping system are evaluated by comparing initial accuracies with those achieved for the following two tests: first, usage of a SPOT image from the same year, but for a different area within the Baichi catchment; second, usage of SPOT images from multiple years for the same region. The integration of the common knowledge via digital landslide signatures is new in object-based landslide studies. In combination with strategies to optimize image segmentation this may lead to a more objective, transferable and stable knowledge-based system for the mapping of landslides from optical satellite data and DEMs.
With object-based image analysis (OBIA) landslides can be mapped more accurately than with pixel-... more With object-based image analysis (OBIA) landslides can be mapped more accurately than with pixel-based methods. While many authors have recognized the value of segmentation optimization for increasing the objectivity and transferability of landslide mapping, the optimization of the classification step is lagging behind. This study introduces a landslide mapping system that is based on expert knowledge models and implemented in OBIA. These models hold the operational knowledge about landslides and digital landslide mapping such as data, classification features, and feature thresholds. The knowledge was gathered during personal semi-structured interviews of 20 Taiwanese landslide experts. The system was tested for mapping landslides in a sub-region of the Baichi catchment in Northern Taiwan. The potential landslide areas were accurately extracted. The refinement of the potential landslide area into landslide types was mainly based on slope values. Additional expert-based rules will be implemented to increase the accuracy and objectivity of the final landslide classification.
2006 Portland, Oregon, July 9-12, 2006, 2006
Page 1. The authors are solely responsible for the content of this technical presentation. The te... more Page 1. The authors are solely responsible for the content of this technical presentation. The technical presentation does not necessarily reflect the official position of the American Society of Agricultural and Biological Engineers ...
Paddy and Water Environment, 2012
Fallowing with green fertilizer can benefit agricultural ecosystem services (AES). Farmers in Tai... more Fallowing with green fertilizer can benefit agricultural ecosystem services (AES). Farmers in Taiwan do not implement fallow practices and plant green fertilizer because the current subsidy level (46,000 NT$ per ha) is too low to manage fallowing. This paper defines the objective of government agriculture policy or the farmer's objective as maximization of farm productivity, approximated to the value of social welfare and AES. Farms, which do not follow proper fallowing practices, often have poorly maintained fallow land or left farmland abandoned. This results in negative environmental consequences such as cutworm infestations in abandoned land, which in turn can affect crops in adjacent farmlands. The objectives of this study are twofold. First, it determines the proper fallowing subsidy based on the concept of payment for ecosystem services to entice more farmers to participate in fallowing. Second, it simulates the benefit of planting green manure in fallow land to the supply of AES based on the rate of farmers who are willing to participate in fallow land practices and essential parameters that can affect soil fertility change. The approach involves a series of interviews and a developed empirical model. The value of AES when the rate of farmer participation is 100% represents a 1.5% increase in AES (448,317,000 NT$) over the value at the current participation rate of 14%. This study further concludes that the appropriate fallowing subsidy has a large positive impact on AES and social welfare (e.g., benefit from food and biofuel supplies) and is seen as a basis of ecological governance for sustainable agro-ecosystems.
ABSTRACT Landslides occur every year in many areas of the world, causing casualties, economic and... more ABSTRACT Landslides occur every year in many areas of the world, causing casualties, economic and environmental losses. Landslide inventory maps are important to document the extent of the landslide phenomena in a region, for risk estimation and management, and to study landscape evolution. We present a method to facilitate the semi-automatic recognition and mapping of event induced shallow landslides. The method is based on the combination in a Bayesian framework of information extracted from High Resolution optical multispectral satellite images and Digital Elevation Models (DEM). The landslide membership probability is estimated from post-event satellite images using a supervised image classification method. The likelihood of landslide occurrence is obtained adopting a "data-driven" approach, intersecting existing landslide inventories with maps of morphometric parameters (slope and curvature) calculated from the DEM. We tested the method in the Huaguoshan basin, Taiwan, where it proved capable of detecting and mapping landslides triggered by Typhoon Morakot in August 2009. Compared to other pixel-based approaches, the method reduces significantly the typical "salt-and-pepper" effect of landslide classifications, and allows the internal classification of landslide areas in landslide source areas and landslide travel and depositional ("run out") areas.
Natural Hazards, 2012
Landslide mapping is essential for effective watershed management. In Taiwan, a typhoon or earthq... more Landslide mapping is essential for effective watershed management. In Taiwan, a typhoon or earthquake event can trigger hundreds, even thousands, of shallow landslides in mountainous watersheds. Thus, improving the efficiency of landslide mapping by means of remote sensing techniques is an important issue. This study proposes a new method that uses concurrent aerial laser scanning (ALS) data and color ortho-imagery as input data: the topographic indices of slope, surface roughness, and object height model can be derived from the ALS data and the Green-Red Vegetation Index from the orthoimages. The method first uses these topographic and spectral indices in a global, semiautomatic algorithm to separate landslide from non-landslide pixels. It then offers a region growing tool and a 3D Eraser/Painter to edit detected landslides locally. These global and local operations are designed with a user interface, which is intuitive and user-friendly. Results from four test sites in a mountainous watershed prove that the method is easy, accurate, and suitable for landslide mapping in Taiwan.
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Papers by Kang-tsung Chang