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Now showing items 1 - 16 of 20

  • Urban land expansion in Quanzhou City, China, 1995–2010

    Bin Quan   Yijun Bai   M.J.M. Römkens   Kang-tsung Chang   Hui Song   Tao Guo   Shi Lei  

    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. Highlights • Urban land in Quanzhou has increased more than twofold between 1995 and 2010. • Urban land expansion took place in the city districts and around industrial zones in Quanzhou. • Urban land expansion was slower in Quanzhou than Shenzhen and Dongguan. • Quanzhou's reliance on labor-intensive industries has influenced its population growth and urbanization.
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  • Modeling the spatial occurrence of shallow landslides triggered by typhoons

    Kang-tsung Chang   Shou-hao Chiang   Yi-chin Chen   Alessandro C. Mondini  

    Abstract Many shallow landslides in Taiwan are triggered by typhoons (tropical cyclones) during the summer months. Each typhoon produces a different rainfall distribution, depending on its track and position and the atmospheric conditions. This study investigated whether the additional rainfall data in a landslide susceptibility model can improve its performance in predicting typhoon-triggered landslides, and whether information on past typhoon events, combined with an event-based landslide inventory, can help predict landslides triggered by a typhoon. To answer these questions, the study adopted a method that integrates rainfall data with the critical rainfall model (a landslide susceptibility model based on geoenvironmental factors) to derive a logistic regression model for predicting landslide occurrence. Results of a back analysis of landslides triggered by nine typhoons from 2001 to 2009 reveal that, by including rainfall data, the integrated method performs better than the critical rainfall model in the average overall accuracy rate (0.78 vs. 0.45) and the average modified success rate (0.75 vs. 0.68). Our preliminary results also suggest that it is possible to predict landslides triggered by a typhoon by using a catch-all model developed from all other typhoon events in an inventory, or a group model developed from other typhoon events of similar rainfall characteristics in an inventory. This study opens up a new research direction in analyzing rainfall-triggered landslides in Taiwan and elsewhere. Highlights • Additional rainfall data can improve a landslide susceptibility model’s performance. • The integrated model performs better than the critical rainfall model and is transferable. • Information on past typhoon events can help predict landslides triggered by a typhoon. • Information on past typhoon events can be included in catch-all or group models.
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  • Quantifying rainfall controls on catchment-scale landslide erosion in Taiwan

    Yi-Chin Chen   Kang-tsung Chang   Yu-Jia Chiu   Sze-Man Lau and Hong-Yuan Lee  

    Landslide erosion is a dominant hillslope process and the main source of stream sediment in tropical, tectonically active mountain belts. In this study, we quantified landslide erosion triggered by 24 rainfall events from 2001 to 2009 in three mountainous watersheds in Taiwan and investigated relationships between landslide erosion and rainfall variables. The results show positive power-law relations between landslide erosion and rainfall intensity and cumulative rainfall, with scaling exponents ranging from 2·94 to 5·03. Additionally, landslide erosion caused by Typhoon Morakot is of comparable magnitude to landslide erosion caused by the Chi-Chi Earthquake (MW = 7·6) or 22–24 years of basin-averaged erosion. Comparison of the three watersheds indicates that deeper landslides that mobilize soil and bedrock are triggered by long-duration rainfall, whereas shallow landslides are triggered by short-duration rainfall. These results suggest that rainfall intensity and watershed characteristics are important controls on rainfall-triggered landslide erosion and that severe typhoons, like high-magnitude earthquakes, can generate high rates of landslide erosion in Taiwan. Copyright
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  • Preface: Modeling land dynamics in mountainous environments

    Kang-Tsung Chang   Antonie Veldkamp   Marco Borga  

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  • An integrated model for predicting rainfall-induced landslides

    Kang-Tsung Chang   Shou-Hao Chiang  

    This study proposes a novel method that combines a deterministic slope stability model and a statistical model for predicting rainfall-induced landslides. The method first uses the deterministic model to derive the rainfall rate critical to induce slope failure for each land unit. Then it calculates the difference between the critical rainfall threshold and estimated rainfall intensity. Using the difference and estimated rainfall duration as explanatory variables, the method derives a logit (integrated) model to compute landslide occurrence probabilities. To demonstrate the effectiveness of this method, the study used radar rainfall estimates and landslides associated with a typhoon (tropical cyclone) to develop the integrated model and the same types of data associated with another typhoon to validate the model. The model had a modified success rate of 84.0%for predicting landslides and stable areas, and model validation yielded a modified success rate of 87.4%. Both rates were better than those from the critical rainfall model. The main advantage of the integrated model lies in its use of rainfall variables that are not included in calculating the critical rainfall. Also, as a probabilistic model, the integrated model is better suited for decision-making in watershed management. This study has advanced the method for predicting rainfall-triggered landslides.
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  • An integrated model for predicting rainfall-induced landslides

    Kang-Tsung Chang   Shou-Hao Chiang  

    This study proposes a novel method that combines a deterministic slope stability model and a statistical model for predicting rainfall-induced landslides. The method first uses the deterministic model to derive the rainfall rate critical to induce slope failure for each land unit. Then it calculates the difference between the critical rainfall threshold and estimated rainfall intensity. Using the difference and estimated rainfall duration as explanatory variables, the method derives a logit (integrated) model to compute landslide occurrence probabilities. To demonstrate the effectiveness of this method, the study used radar rainfall estimates and landslides associated with a typhoon (tropical cyclone) to develop the integrated model and the same types of data associated with another typhoon to validate the model. The model had a modified success rate of 84.0%for predicting landslides and stable areas, and model validation yielded a modified success rate of 87.4%. Both rates were better than those from the critical rainfall model. The main advantage of the integrated model lies in its use of rainfall variables that are not included in calculating the critical rainfall. Also, as a probabilistic model, the integrated model is better suited for decision-making in watershed management. This study has advanced the method for predicting rainfall-triggered landslides.
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  • Comparing urban land expansion and its driving factors in Shenzhen and Dongguan, China

    Jianfei Chen   Kang-tsung Chang   David Karacsonyi   Xiaolin Zhang  

    Abstract China has been the engine of global urban population growth, with nearly one-third of the global urban population growth realized in China in 2000–2010. This rapid process of urbanization will continue in the coming decades based on media reports, thus raising concerns about urban land expansion and sustainable urban development in China. Using satellite images and government statistics as data sources, this study compared urban land expansion in Shenzhen and Dongguan, two adjacent and sometimes competing cities in the economically most dynamic region of China. Our data show that the two cities were similar in urban land expansion rate and intensity in 1990–2008 but Shenzhen had higher population growth and urban population density than Dongguan during the period, suggesting that Shenzhen had achieved a higher level of sustainable urban development than Dongguan. To explain this difference, we analyzed the driving factors and found that (1) Shenzhen was more successful than Dongguan in transforming its industrial structure to develop more capital- and technology-intensive industries; (2) Shenzhen had much higher total GDP and per capita GDP than Dongguan; (3) Shenzhen had benefited from a number of government policies targeted at the city's economic development; and (4) in addition to geographically adjacent to Hong Kong, Shenzhen had better transportation facilities than Dongguan, including an international airport and three container ports. Through these favorable driving factors, more people had moved into Shenzhen and, in the process, helped transform the city to become more sustainable in its urban development. The findings of this study can help us better understand urbanization in China. Highlights • This study prepared land use maps of Shenzhen and Dongguan in 1990, 1999, 2005, and 2008. • The study used six indices to measure urban land expansion, population growth, and their relationship. • Shenzhen and Dongguan had similar urban land expansion rate and intensity in 1990–2008. • Shenzhen had higher population growth and urban population density than Dongguan in 1990–2008. • Shenzhen had more favorable industrial structure, GDP, transportation, and policy than Dongguan.
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  • Change in Environmental Benefits of Urban Land Use and Its Drivers in Chinese Cities, 2000–2010

    Xiaoqing Song   Kang-tsung Chang   Liang Yang   Jürgen Scheffran  

    Driven by rising income and urban population growth, China has experienced rapid urban expansion since the 1980s. Urbanization can have positive effects on the urban environment; however, improvement of urban environment quality, especially its divergence between relatively developed and undeveloped cities in China, is currently a rather rudimentary and subjective issue. This study analyzed urban environmental benefits among China’s prefectural cities based on their structure of urban land use in 2000 and 2010. First, we divided 347 prefectural cities into two groups, 81 coastal and capital cities in the relatively developed group (RD) and 266 other prefectural cities in the undeveloped group (RP). Then, we defined three areas of urban environmental benefits, including green infrastructure, industrial upgrade, and environmental management, and developed an assessment index system. Results showed that all prefectural cities saw improvement in urban environmental quality in 2000–2010. Although the RD cities had higher income and more population growth, they had less improvement than the RP cities during the same period. We also found that demographic and urban land agglomeration among RD cities restrained green infrastructure expansion, making green infrastructure unsuitable as a permanent solution to environmental improvement. It is therefore urgent for China to promote balanced improvement among the three areas of urban environmental benefits and between the RD and RP cities through regional differentiation policies.
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  • Investigating urbanization and its spatial determinants in the central districts of Guangzhou, China

    Yingbiao Chen   Kang-tsung Chang   Fuzhuang Han   David Karacsonyi   Qinglan Qian  

    Abstract Like many cities on the east coast of China, Guangzhou has experienced dramatic urban growth since the late 1970s and become the largest metropolis in southern China. This study examined urbanization in the central districts of Guangzhou in two parts: (1) analyzing the spatiotemporal changes of urban land expansion from 1980 to 2010, and (2) analyzing the spatial relationship between urban land ratio and its determinants in not fully built-up areas in 2010. Results from the first part showed that the study area's urban land doubled during the three decades but the rate of expansion had slowed down considerably after 1990. The expansion was primarily in the eastward direction away from the old city center, in a process combining outlying growth, infill, and edge expansion. Results from the second part revealed that, due to the spatial autocorrelation of urban land ratios, spatial regression performed better than ordinary least squares regression in explaining their spatial distribution. Among the determinants in the spatial regression models, road density and distances to transportation services, bank, and hotel were most important, followed by distances to company office and major road, suggesting the importance of convenient daily transport to urban residents. The two spatial regression models were consistent in both the performance statistics and the selection of significant explanatory variables, thus confirming the usefulness and reliability of spatial regression in modeling urban land patterns. These results are relevant to studies of the urban condition and urban planning in Guangzhou as well as rapidly urbanizing China. Highlights • Urban land in Guangzhou's central districts doubled in 1980–2010. • Spatial regression performed better than ordinary least squares regression in modeling urban land ratios in 2010. • Road density and proximity to transportation services, bank, and hotel were the most important spatial determinants. • The study verified the importance of a well-designed road network in rapidly urbanizing China.
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  • Analysing the Relationship Between Typhoon-Triggered Landslides and Critical Rainfall Conditions

    Kang-tsung Chang   Shou-Hao Chiang   Feng Lei  

    Abstract Many landslides are triggered by rainfall. Previous studies of the relationship between landslides and rainfall have concentrated on deriving minimum rainfall thresholds that are likely to trigger landslides. Though useful, these minimum thresholds derived from a log–log plot do not offer any measure of confidence in a landslide monitoring or warning system. This study presents a new and innovative method for incorporating rainfall into landslide modelling and prediction. The method involves three steps: compiling radar reflectivity data in a QPESUMS (quantitative precipitation estimation and segregation using multiple sensors) system during a typhoon (tropical hurricane) event, estimating rainfall from radar data and using rainfall intensity and rainfall duration as explanatory variables to develop a landslide logit model. Given the logit model, this paper discusses ways in which the model can be used for computing probabilities of landslide occurrence for a real-time monitoring system or a warning system, and for delineating and mapping landslides. Copyright © 2007 John Wiley & Sons, Ltd.
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  • Modeling typhoon- and earthquake-induced landslides in a mountainous watershed using logistic regression

    Kang-Tsung Chang   Shou-Hao Chiang    Mei-Ling Hsu  

    Landslides can be caused by storms and earthquakes. Most logistic regression models proposed in recent years have been targeted at rainfall-induced landslides. In areas such as Taiwan, where landslides can be triggered by typhoons (tropical cyclones) and earthquakes, a rainfall-induced model is insufficient because it provides only a partial explanation of landslide occurrence and overlooks the potential effect of earthquakes on typhoon-triggered landslides. This study used landslides triggered by a major earthquake and a typhoon prior to the earthquake to develop an earthquake-induced model and a typhoon-induced model. The models were then validated by using landslides triggered by three typhoons after the earthquake. According to the results, typhoon-triggered landslides tended to be near stream channels and earthquake-triggered landslides were more likely to be near ridge lines. Moreover, a major earthquake could still affect the locations of typhoon-triggered landslides 6 years after the earthquake. This study therefore demonstrates that an earthquake-induced model both sheds light on the environmental factors for triggering landslides, and augments a rainfall-induced model in its predictive capability in areas such as Taiwan.
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  • Modeling typhoon- and earthquake-induced landslides in a mountainous watershed using logistic regression

    Kang-Tsung Chang   Shou-Hao Chiang   Mei-Ling Hsu  

    Landslides can be caused by storms and earthquakes. Most logistic regression models proposed in recent years have been targeted at rainfall-induced landslides. In areas such as Taiwan, where landslides can be triggered by typhoons (tropical cyclones) and earthquakes, a rainfall-induced model is insufficient because it provides only a partial explanation of landslide occurrence and overlooks the potential effect of earthquakes on typhoon-triggered landslides. This study used landslides triggered by a major earthquake and a typhoon prior to the earthquake to develop an earthquake-induced model and a typhoon-induced model. The models were then validated by using landslides triggered by three typhoons after the earthquake. According to the results, typhoon-triggered landslides tended to be near stream channels and earthquake-triggered landslides were more likely to be near ridge lines. Moreover, a major earthquake could still affect the locations of typhoon-triggered landslides 6 years after the earthquake. This study therefore demonstrates that an earthquake-induced model both sheds light on the environmental factors for triggering landslides, and augments a rainfall-induced model in its predictive capability in areas such as Taiwan.
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  • Spatial analysis of habitat selection by Sitka black-tailed deer in Southeast Alaska, USA

    Kang-Tsung Chang   David L. Verbyla   Jeffrey J. Yeo  

    We used a vector-based geographic information system (GIS) to examine habitat selection by radiocollared Sitka black-tailed deer (Odocoileus hemionus sitkensis) in logged forests of southeast Alaska. Our main objective was to explain deer habitat selection relative to old-growth/clear-cut edges and edge habitats at two different spatial scales. Deer home ranges contained higher percentages of recent clear-cuts (50-69%) than the study area (37%; P lt 0.01) and had higher old-growth/clear-cut edge densities than expected by chance (P lt 0.01). Deer relocation points were closer to old-growth/clear-cut edges (average = 135 m) than random points located within each deer's relocation area (average = 168 m; P = 0.05). Likewise, deer relocations were closer to old-growth/clear-cut edges than points randomly located within old-growth stands or recent clear-cuts (P lt 0.01). As the size of clear-cuts increased, both deer relocation density and the proportion of a clear-cut occupied by deer home ranges decreased. Because old growth is important deer habitat and clear-cuts can produce deer forage for only 20-30 years after logging in southeast Alaska, deer management plans such as preserving entire watersheds and maintaining mixes of old growth and recent clear-cut have been proposed. Our data suggest that deer need a diversity of habitats near each other within their home ranges.
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  • Reply to Reid and ó hUallacháin

    Kang-tsung Chang  

    No abstract is available for this article.
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  • JAPAN\"S DIRECT MANUFACTURING INVESTMENT IN THE UNITED STATES

    Kang-tsung Chang  

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  • Average landslide erosion rate at the watershed scale in southern Taiwan estimated from magnitude and frequency of rainfall

    Yi-chin Chen   Kang-tsung Chang   Hong-yuan Lee   Shou-hao Chiang  

    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 mmyr − 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 mmyr − 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. Highlights • We use rainfall magnitude and frequency to estimate average landslide erosion rate. • We validate estimated landslide erosion rate with rates using other methods. • We simulate uncertainty of landslide erosion rate by length of landslide record. • The study highlights the importance of extreme rainfall events in landslide erosion.
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