Hydrology :Treats of the water of the earth, their 
    occurrence, circulation and
   distribution, their chemical & physical properties and 
    their reaction with their
   environment, including their relation to living things.
   Weather and Hydrology: In hydrologic problems 
    metrology plays an
   important role which includes the determination of 
    probable max. precipitation
   for spillway design and determination of probable 
    max. winds over water surface
   for evaluating resulting waves in connection with the 
    design of dams.
   Hydrological cycle: Various aspects of water related to 
    the earth can be
   explained in terms of a cycle known as the 
    hydrological cycle.
    Engineering applications at the hydrologic cycle are found in the 
     design and
    operation of projects dealing with water supply, irrigation and 
     drainage, water
    power and flood control. In all of these projects hydrological 
     investigations for
    the proper assessment of the following factors are done:
    1- The capacity of storage structures such as reservoirs.
    2- The magnitude of flood flows to enable safe disposal excess flow.
    3- The min. flow and quantity of flow available at various seasons.
    Solar and earth radiation: Solar radiation is the earth’s chief source of
    energy and it determines weather and climate.
    Radiation wave lengths are usually given in micrometers (μm) = (10-
     6m)
    Solar radiation is in short waves and its max. energy is in the range 
     of 0.4–0.8μm
    Earth radiation is in long waves and is about 10μm.
    A large part of the solar radiation reaching the outer limits of the 
     atmosphere is
    scattered and absorbed in the atmosphere or reflected from clouds 
     and the earth
    surface.
    Properties of water vapor:
    Evaporation: or vaporization, is the process by which liquid water is 
     converted
    in to vapor.
    Sublimation: is the direct transformation from ice to vapor and vice 
     versa.
    Condensation: is the process by which vapor changes to the liquid 
     then to the
    solid state.
    Vapor presser: is the partial presser exerted by water vapor.(ℓ)and it 
     would be
    the difference between the presser of the moist air and that of the 
     dry air.
    ℓ=p-p`
    Where:
    ℓ=vapor presser.
    P=total presser of the moist air.
    p`=final presser of the dry air.
    Saturated vapor presser: is the presser exerted by the vapor in a 
     saturated
    space.
    Relative humidity: is the percentage ratio of the actual to the 
     saturated vapor
    presser.
    *Evaporation removes heat from the liquid being evaporated while 
     condensation
    adds heat.
   Questions??