In the last two posts here (one of which you got twice, my apology), I’ve been trying to ‘revision’ the Colorado River as the classic desert river that it is. All rivers are composed of runoff – water from precipitation that did not soak into the ground, collecting in streams that ‘run off’ to the next lower watershed. Humid-region rivers receive new water from unused precipitation all the way along their course to the sea, but a river in the arid lands obtains nearly all of its water as runoff from a highland area high enough to force water vapor to condense into precipitation. The resulting runoff from that precipitation then flows down into the arid lands where it receives very little additional moisture and thus starts to diminish through natural processes on its way to the sea – evaporation under the desert sun, riparian vegetation use, absorption into low desert water tables. When the deserts are large enough, and … Read More