Water Throughput

You can think of the hydrological cycle as small buckets of fast-recycling water spread very unfairly around the globe.  Norway has 82,000 cubic meters of renewable freshwater per person, while Kenya has just 830.  This unfair distribution of surface water is caused by the pattern of the global atmosphere circulation itself - - and climate change may have a significant disruptive influence on our current patterns of fairness and unfairness.

This is why fresh water throughput is more important than absolute volume.  Water volume in rivers at any point in time is small - - what is critical for humans and ecosystems is the overall system throughput - - how fast a water droplet flows down a river.  Our current water systems are "small storage" but "fast throughput" systems.  Our dams, reservoirs, and artificial impoundments history tells the story.  On a global basis, we have produced in our collective engineering histories a water storage system of only 7,200 cubic kilometers for a global water withdrawal rate of 3,800 cubic kilometers per year.  Roughly a two year average stored supply of water.  Granted, averages are misleading for resources such as water in which the micro drives the macro - - but it provides an important baseline when discussing climate change.  It also highlights the primary reason why our water throughput systems, where the atmosphere and rivers have no meaningful storage capacity in some parts of the world from which to draw water in dry times or hoard in wet times are so fundamentally vulnerable to potential shocks and changes in climate patterns that impacts the hydrological cycle.