🏜️ Bare Soil Evaporation: Dry Layer, Vapour Diffusion, Day-Night Heating and Gravel Mulch

Water leaves dry-skinned soil only as vapour creeping up through a thickening dry layer. Follow a 30 cm cutaway through day and night: the evaporation front sinks as the square root of time, the temperature wave is damped with depth, wind stops mattering, and a gravel mulch adds a resistance.