Trend Human disturbance of streamflow and soil moisture keeps spreading

Summary

The freshwater boundary measures how far streamflow (blue water) and plant-available soil moisture (green water) depart from a pre-industrial-like state largely free of human influence. The latest analysis finds abnormally dry or wet deviations on 22.6 percent of ice-free land for blue water and 22.0 percent for green water, roughly double pre-industrial conditions and above the boundaries of 12.9 and 12.4 percent. Both measures began climbing in the early twentieth century, crossed their boundaries around 1940 and have kept rising. The report judges that climate change has become the dominant global driver of this transgression over the past century, while withdrawals, river regulation and land-use change especially intensify dry deviations. Dry deviations can deplete wetlands and lakes and fuel drought, fire and carbon release, while wet deviations can bring extreme floods and permafrost thaw. Because the model record ends in 2019, the current status reflects average conditions over 2010 to 2019.