دانلود رایگان مقاله تغییرات خط ساحلی در افزایش سطح آب اقیانوس

Abstract

Low-lying reef islands are considered highly vulnerable to the impacts of climate change. Accelerating rates of sea level rise as a result of anthropogenic climate change are expected to destabilise islands and threaten to render entire nations uninhabitable. Using historic aerial photographs and recent highresolution satellite imagery, shoreline changes on six atolls and two mid-ocean reef islands in the Republic of the Marshall Islands were analysed. Results reveal that since the middle of the 20th century more shoreline has accreted than eroded, with 17.23% showing erosion, compared to 39.74% accretion and 43.03% showing no change. The net result of these changes was the growth of the islands examined from 9.09 km2 to 9.46 km2 between World War Two (WWII) and 2010. Analyses of shoreline changes since the 1970s show that shorelines are accreting albeit at a slower rate, with rates of change between the 1970s and 2010 of 0.29 m/dec compared with 0.77 m/dec between WWII and 1970s. The observed shoreline changes occur in the context of locally rising sea level. As sea level continues to rise there is a critical need for regular monitoring of reef islands in order to better understand the spatio-temporal variability of reef island change and guide future adaptation efforts within atoll nations

5. Discussion

The dataset comprises observations from 127 islands in the Marshall Islands over a period coincident with local sea level rise of 2.2 mm/yr (Becker et al., 2012). Of note, no islands were completely eroded from their reef platform over the time period of analysis. Rather the dominant mode of shoreline change was accretion. The analysis of all shoreline changes between WWII and the most recent satellite imagery utilised in this study reveals 39.87% of shorelines underwent statistically significant accretion while 18.19% eroded and 41.95% exhibited no detectable change. Analysis of all shoreline change between the 1970s and 2010 shows a slightly higher proportion shoreline accretion compared with erosion (28.46% vs 24.65%). Collectively the outcome of shoreline changes over both time periods considered in this study was the growth of islands, resulting in an increase in the areal extent of islands throughout the Marshall Islands of approximately 4% (Table 3). Our observations are at odds with widespread assertions that the islands are currently being destabilised and eroded. However, the findings of this study are broadly consistent with island stability and island growth documented on other atolls since the mid-late 20th century (Webb and Kench, 2010; Yates et al., 2013; Ford, 2013; Kench et al., 2015).