Environment: Water, water, everywhere?

Changes in global surface water distribution over the past 30 years are mapped at high-resolution in a paper published online in Nature this week. The study suggests that drought, reservoir creation (such as dam building) and water extraction seem to drive most of the changes.

Previous studies have mapped the global distribution of surface water and tracked local and regional changes in surface water over time. However, a global and methodologically consistent quantification of changes in surface water over time did not exist, until now.

Jean-Francois Pekel and colleagues analysed over three million Landsat images, taken between 1984 and 2015, to quantify month-to-month changes in surface water at a resolution of 30 metres. They use an algorithm to classify each 30 m × 30 m square as either land or open water (including both fresh and saltwater, but excluding the oceans). The authors show that over the past 32 years permanent surface water has disappeared from an area of almost 90,000 km2, roughly equivalent to that of Lake Superior, with 70% of that loss occurring in the Middle East and Central Asia. However, they also show that new permanent surface water has formed elsewhere, covering an area about double that from which water was lost (184,000 km2), and that all continental regions show a net increase in permanent water except Oceania, which experienced a 1% net loss.

The authors conclude that their new data set provides an additional resource on the impact of climate change and climate oscillation on surface water distribution, while also capturing the effects that humans have on surface water resource distribution.