Environmental Monitoring and and Change Analysis of Mountainous Areas Subject to Climate Change

ABSTRACT

As one of the top three countries suffering from threats of debris flows, the overall plans of slopeland treatment and disaster prevention have been the ultimate goal that the government tries to achieve. Concerning aspects of erosion control, disaster prevention, conservation, and sustainable development, the Soil and Water Conservation Bureau (SWCB) has employed various engineering practices in terms of gully erosion and landslides, such as methods of check dam, submerged dam, river regulation, revetment, levee, and drainage. In recent years, the key concepts of ecological engineering methods, energy conservation, and carbon reduction are highly valued and advocated. However, it is crucial to track and assess the effects of management practices while considering the landscape variations and disaster susceptibility analysis of critical watersheds.

To get the results of management practice effects of critical watersheds and historical changes in disaster susceptibility, this project aims to employ multi-date satellite images from Formosat-2 satellite and SPOT (processed through procedures of coregistration, orthorectification, geometric registration, radiance normalization, spectral summation intensity modulation, edge sharpening and adaptive enhancement) in landscape variation analysis. By overlay the data of engineering sites to distinguish critical watersheds, sub-watersheds, and slopelands, this project then outlines the areas that might be influenced by disasters according to the land use maps and the protected objects data. Furthermore, this study applies three quantitative methods. The first method is to use the Normalized Difference Vegetation Index (NDVI), Greenness index, and gradient to delineate vegetation areas. The second one employs pre- and post-disaster images with the DEM (Digital Surface Model) to delineate landslide areas. The third one applies the data of river course maps to delineate the variation of river courses. The interpretations of landslides and river courses are significant resources for the quantitative analysis which provides management practice effects on critical watersheds for further discussion and further investigation of the landscape variations and disaster susceptibility as references for future management targets as well as management works in order of priority.

In the first stage, this project establishes a database and proceeds a thorough analysis of twenty-eight sub-watersheds in northern Taiwan area, including twenty-two sub-watersheds within critical watersheds and six additional sub-watersheds within areas severely devastated by Typhoon Soudelor. This year, six sub-watersheds are selected for aerial photography and onsite investigation to get the most updated and high-spatial-resolution aerial photos of the important engineering works and critical watersheds. Two terms of pre- and post-engineering photography will be conducted and the DEM will be established in order to distinguish the landscape variations and to establish the database. When natural disasters occur, the changes in critical watersheds can be quantitatively evaluated by comparing the before- and after-data, which would significantly benefit the detailed management practice effects.

Combined with the results of detailed survey, engineering, and aerial photos, two versions of videos (in Chinese and in English) and a poster will be made to promote the effects of management practices; the data acquired by this project will provide for several engineerings, including the River Management for the Taiban Creek, the Tsukeng Drawbridge Wildcreek Project, and the Zhongpu No. 10 Bridge Upstream Rehabilitation Project, to win the Public Construction Golden Quality Award.

This project also focuses on evaluating the sliding areas of watersheds and its standard deviation through the integration of satellite images, the historical list of landslides, and the optimal subdivision of watersheds for landslides. The investigation of landslides situations enables the project to conduct the classification of stability index and adequately controls the variation of sub-watersheds. With the application of multi-satellite data and long-term monitoring of watersheds, this project is able to keep tracking down the environmental changes and further develops the automatic interpretation of landscape variation data; once natural disasters occur, the government can conduct instantaneous monitoring of critical watersheds. Additionally, through the data of rainfall simulation provided by the Taiwan Climate Change Projection and Information Platform Project (TCCIP), this project analyzes the impact of the variation of rainfall intensity caused by typhoons on landslides as references for future estimation of high disaster potential areas.

This project establishes a database of landscape variations by integrating the long-term satellite images, open data satellite images, and the results of interpretations. The following three primary functions will provide the colleagues in the SWCB with online application, assisting in the policy making concerning disaster prevention: establishing the stability index based on the results of previous surveys, applying the open data to develop the automatic interpretation for monitoring landscape variations, and integrating forecasting of future precipitation influenced by climate change to discuss landslide potential.

Keywords:Multi-satellite, critical watersheds, stability index, the effects of management practices, automatic variation analysis, climate change