mally raise to the benefit of other plants sink below reach as the
groundwater sinks. This is the cause of desertification, now becom-
ing prevalent in many tropical areas. The groundwater disappears,
probably for ever, into the womb of the Earth where it came from.
The limited circulation of the half water cycle increases the inten-
sity of thunderstorms. These can raise the water vapour to levels far
higher than normal. At altitudes of 40-80 kilometres it is exposed to
much stronger ultraviolet and high-energy gamma radiation, which
break up the water-molecule, separating the hydrogen and oxygen
The HALF CYCLE in contrast, has the following features:
Evaporation from oceans;
Rising water vapour;
Cooling and condensing;
Formation of clouds;
Precipitation as rain;
No infiltration due to negative temperature gradient;
Rapid runoff over the ground surface;
No groundwater recharge;
Sinking water table — in the long term;
Cessation of natural supply of nutrients to vegetation;
Under certain conditions, major flooding can occur;
Excessively fast re-evaporation;
Oversaturation of atmosphere with water vapour;
Rapid reprecipitation as storm rain.
Fig. 9.2. The half hydrological cycle.- THE HYDROLOGICAL CYCLE