Land-ocean interaction Interpretation through remote sensing image analysis in North Korean coastal area

Land-ocean interaction in coastal area is mainly accelerated by changes of socioeconomic drivers such as population concentration, economic growth and its related deforestation. Our society has witnessed decrease and degradation of coastal ecosystems, as a consequence of socioeconomic change. North Korea reclaimed coastal wetlands historically for securing more agricultural lands. However, the extent of coastal wetlands in North Korea did not suggest typical consequence of land-ocean interaction, i.e. shrink of the wetlands extent. Accretion of coastal wetlands in North Korea appears to be quite different from findings of neighboring countries, China and South Korea.

To interpret abnormal feature of the coastal wetland change in North Korea, we assessed the last 30 years long changes of terrestrial area and coastal wetlands in North Korea. First, the assessment of tidal wetland extent was conducted through analysis of the Landsat images on decadal basis. To exclude the areal loss of tidal flat due to the land reclamation, the hinterland of the current coastline had subtracted in advance. As a result, the extent of tidal flats in North Korea had expanded as 15% from 1980s to 2010s.

Next, the amount of land degradation and sediment discharge were also estimated by use of AVHRR image based proxy data with five years intervals. Mean-maximum NDVI values of autumn after the monsoon season in summer, in large-scale river basins, suggested that the vegetation coverage has decreased ＞10% after the 1995, the period of North Korea’s famine, consequentially causing the increase of TSS concentration in coastal water.

Our findings are suggesting that the change in the frequency of heavy rain has accelerated land degradation, and land use conversion from forests to farmlands caused devastating floods in North Korea. Ironically, the increase of sediment discharge driven by land cover change has brought increase of tidal wetlands by providing more materials to coastal ecosystem.