Global occupation of wetland by artificial impervious surface area expansion and its impact on ecosystem service value for 2001–2018

Wetland is one of the most critical ecosystems with various functions, it produces the highest ecosystem services value (ESV) per unit area among all land types, thus, its decline has become a global concern in recent years. Since the 21st century, many developing countries have been continuously encroaching on wetlands due to rapid economic and population growth, resulting in the replacement of a large number of wetlands by cities, and how to reconcile urban expansion and wetland conservation has become a significant problem that needs to be considered. In this context, we mapped the spatial distribution of wetlands occupied by the expansion of global artificial impervious surface area (ISA) for 2001-2018 and discussed its temporal and spatial change characteristics at the global, continental, and national scales using the annual maps of global annual impervious area data set and global dynamic land cover data set based on Google Earth Engine platform, the loss of ESV due to wetland occupation was also measured at each spatial scale level. The results show that: (1) A total of 1301.24 km(2) of wetlands were occupied by ISA expansion globally for 2001-2018, and their interannual variation showed an upward trend for 2001-2015, then began to decline rapidly since 2016. The occupation results in a global loss of US$3.46 billion in ecosystem service value; (2) Asia has the highest loss of ESV due to occupation of wetlands by ISA expansion, 624.18 km(2) of occupation of wetlands resulted in a loss of US$1.66 billion in ESV, making it the continent with the largest area of occupied wetlands. Taking into account the different sizes of the continents, Oceania is the continent where ISA expansion occupies the wetlands most, while South America is the continent where it is relatively least severe; (3) China, the USA and Russia account for 50.9 % of global ESV loss due to wetland occupation by ISA expansion, a total of 663.95 km(2) of wetlands were occupied. Although countries have made great efforts to protect wetland resources and deal with urban land expansion, our results show that the problem of wetlands occupied by global urban land expansion is still severe.