Māris kļaviņŠ, azamat azizov, JĀnis zaļoksnis environment, pollution, development: the case of uzbekistan

Figure 3.2. 
Hydrological 
cycle

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24 
ENVIRONMENT, POLLUTION, DEVELOPMENT:  THE CASE OF UZBEKISTAN
The particles formed from the impact of cosmic radiation can also 
cause water condensation. The condensation processes take place at 
the upper layers of the atmo sphere as well as on the Earth’s surface. 
Precipitation occurs in a variety of forms, including rain, snow and 
hail. When water evaporates in the atmo sphere, it becomes subject 
to the atmo spheric diffusion. Consequently, the water vapour, which 
is mostly formed above the surface of seas and oceans, can be 
carried to great distances along with the movement of air masses, 
until it finally falls out on the continents as well.
Atmo spheric  precipitation  can  form  a  snow  cover,  it  can  be 
assimi lated by plants or absorbed in the soil, replenishing the under-
ground water resources. Furthermore, one of the most important 
water movements is its accumulation in river basins and subsequent 
surface  runoff  with  rivers.  With  this,  the  water  cycle  is  complete. 
Water can stay in each of the abovementioned environ ments for a 
different  period  of  time  (water  residence  time).  The  duration  of  a 
water turnover period depends on the mass of water in the respective 
environ ment (for example, oceans contain most of the water mass 
that undergoes the hydrological cycle) and on the intensity of 
processes that the water is subject to in the respective environ ment. 
The duration of the period in which water completes a full cycle in 
the  oceans  and  seas  is  estimated  as  approximately  4000  years;  in 
lakes – approximately 10 years; for underground waters – from a few 
weeks to 10 000 years; for glaciers – from 100 to 10 000 years; in the 
atmo sphere – approximately 10 days.
An  essential  factor  for  the  hydrological  cycle  is  the  character 
of the largest water mass – the World Ocean, particularly its water 
currents. Currents on the ocean surface are generated by the inter-
action of wind, the Earth’s rotation (the Coriolis force) and thermal 
factors. The warm water surface currents move a huge amount of 
heat energy from the tropical zones of the World Ocean to the tem-
pe rate and arid climatic zones. In effect, the climate becomes much 
milder in vast areas of dry land. The cold currents, in turn, chill the 
tropical regions.
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