Spatio-temporal characteristics of the mainland coastline utilization degree over the last 70 years in China

• ICUD was built to valuate impacts of human activities on coastline.
• Coastline utilization degree variations were detected at three scales.
• Mainland coastline utilization degree rose significantly over the nearly 70 years.
• There's notable spatio-temporal variability of human impacts on coastline.
• Coastal development and utilization in the northern part surpassed the southern part after 1990s.

Based on topographic maps and remote sensing imageries measured or captured at time instants varied from 1940s to 2012, mainland coastline in 1940s, 1960s, 1990, 2000, 2010 and 2012 in China were delineated and classified into eight types according to the differences in anthropogenic utilization. And the index of coastline utilization degree (ICUD) was defined and calculated for mainland coastline at national, provincial and local scales respectively. It turned out that, 1) over the last 70 years, especially during the last two decades in China, the ICUD increased continuously and dramatically, which shows that the impacts of human beings on mainland coastline increased incessantly. 2) Significant spatial patterns and temporal variations of the ICUD could be observed, in specific, the Yangtze River delta had much higher ICUD in the early stages; however the ICUD in the Pearl River delta and Circum Bohai Bay increased more dramatically than the Yangtze River delta in the last two decades. 3) At national and provincial scales, the intensive and accelerated exploitation of coastline, following the continual decrease of natural coastline over the last 70 years had determined the temporal trends of ICUD. However, the spatio-temporal patterns of ICUD exhibited much complicated characteristics at local scale because both human activities and physical factors had significant impacts on coastline changes. 4) Overall, the ICUD effectively revealed the spatio-temporal characteristics of mainland coastline changes and impacts of human activities on coastline in China. It will be helpful for China's ICZM decision makings to monitor the mainland coastline changes and analyze its dynamics by ICUD.