the global hydrological cycle from the perspective of systems approach

A system may be defined as a set of objectives that are considered together by studying their relationships to each other & their individual attributes. Systems are classified into 3 types:-

a)Isolated system:-are those in which the boundaries for the input of energy & output or export of mass & matter are closed or fixed;

b)Closed system:-are those whose boundaries are fixed & mass & matter can't cross the system boundary i.e., after initial input of matter no further input can be made into the system but there is no binding into the amount of output or input of energy in or out of the system.

c)open system:-are those wherein there is continuous input & output of energy.

                   Cyclic mechanism on the other hand refers to a mechanism that ends at that point from where it has begun.

                    Hydrological cycle is called a cyclic mechanism because it ends from where it has started.

In reality however, the systems are rarely impermeable & aren’t self-contained. Instead, matter & energy flow into & out of the systems across it's boundaries as inputs & outputs called open & closed system. For example:-in drainage basin rainfall is an input & discharge is output & is a complex process goes on in between in the form of basin hydrological cycle. the sum of all the basin hydrological cycle of the world gives rise to the global hydrological cycle. however, the hydrological cycle of the individual basins are an open system. This is generated inside the drainage basin but has been brought from outside by several climatic factors. The energy is in the form of solar energy which also comes from out side the boundary of the drainage basin. The discharge which is the output is'nt returned.

    Basin hydrological cycle is an example of a system because it comprises of the folowing components of which a system is composed, they are as follows:-

a)Organic components:- Plants (which transpires),other organisms including man;

b)Inorganic components:- this includes the physical environment like the air,insolation,landform characteristic of the catchment area;

c)Energy components:-solar,geothermal energy etc.

                  Global hydrological cycle is composed of 3 components:-

a)Organic components:- Plants (which transpires),other organisms including man;

b)Inorganic components:- this includes the physical environment like the air, insolation, landform characteristic of the whole world,sea,oceans,ground water etc.;

                             The use of the systems approach as an analytical tool providing a methodological framework for the investigating basic aspects that are complex interrelated wholes,requires 3 basic aspects that has to be emphasized. These are structure,function & development.

structure is the su of all the components & the connection between them. Function concerns the flows (exchange relationship) which form the connections & development considers changes in both the structure & function which takes place over time.

In the glibal hydrological cycle structure includes – landmass (which contains water:-fresh & saline water in the lakes+ ground water; glaciers),water bodies (rivers, lakes, seas, oceans) & atmosphere(water is present here in the form of water vapour etc.)

Function involves conversion of water into 3 different phases (like:- solid, liquid & gas)the process which leads to conversion from water to water vapour includes evapotranspiration & one which leads to water from water vapour is condensation & precipitation. Freezing converts water to ice. the energy input comes from external sources outside the earth(Sun) & a part is lost to maintain the heat budget of the earth. Solar energy runs the hydrological cycle at the macro & at the micro scale. The example that the water vapor can’t go beyond a certain height of the atmosphere is an evidence that global hydrological cycle is a closed system. There are daily renewed inputs in the form of solar energy followed by daily output of energy. There is no incursion of matter(i.e.) water in this system from outside the globe after the initial input at the time of formation of this planet. If we sum up all the water present in different forms on this planet we will get 100% as the result. this implies that process of hydrological cycle work in such a manner that the output of one of the processes becomes a important for the other processes & there is no by-product as such.