Salinity in both the rivers and on the land is one of the main and most costly
results of overclearing and irrigation. Salinity is caused by changes in the
delicate balance between surface water and groundwater systems. A small increase
in the infiltration of water from the topsoil to the groundwater, due to
rainfall or irrigation, can result in a dramatic rise in groundwater pressure
and watertable levels.

The trees of the open forests are now replaced by shallow-rooted crops and
pastures which absorb far less water than the native trees. Those trees had been
massive water pumps, sucking up moisture from deep underground and putting it
back into the atmosphere through the evaporation from their leaves. With those
pumps gone, ...