What is residence time and what are the average residence time for some of the major water reservoirs on earth?
Residence time is the amount of time that an object stays in one area.
As for the average residence time, there are a ton of major reservoirs and lakes, so I can't cover all of them, but I'll show some of the most extreme. Residence times can vary greatly depending on the reservoir. Some are extremely long, like Lake Tahoe in Nevada with a residence time of 650 years, or Lake Eucumbene in Australia with a residence time of 1953 years. Others are very short, like New Zealand's Lake Arapuni with a residence time of just 1 week, or Switzerland's Lake Cristallina with a residence time of 2-4 weeks.