Define the term hydrological cycle.

KCSE Geography Paper 1 2017 Section B Question 9.

(a) (i) Define the term hydrological cycle. 

• Hydrological cycle is the continuous movement of water from the air to the earth surface and back to the air.

​(ii) Give three factors that influence the occurrence of surface runoff.

•  The amount of rainfall
•  The gradient of the land
•  The nature of the rocks/soil
•  The watertable
•  Vegetation

(iii) State the significance of the hydrological cycle. 

•  Evapotranspiration increases water in the atmosphere
•  It helps to regulate the surface water/underground water and water in the atmosphere.
• It provides underground water through percolation.
•  Large rivers drain into oceans and lakes to form water bodies.
•  Water evaporates from the ground causing drying up of water bodies/arid conditions.
•  It controls the elements of weather such as temperatures/humidity and rainfall.
•  Water vapour maintains the heat energy in the atmosphere
•  Moisture in the atmosphere influences both solar/ terrestrial radiation.

(b) Describe how the following lakes were formed.
(i) morraine dammed lake 
(ii) oxbow lake 

i. Morraine dammed lake

•  It is formed when the valley glacier melts and moraine is deposited across the glacial troughs.
•  The moraine forms a barrier and melt water collects behind it to form a moraine dammed lake.
•  The water accumulates to form a moraine dammed lake.

ii. Oxbow lake

•  A meandering river erodes the outer bank of a meander and deposits material in the inner river bank.
• This deposition continues until a narrow piece of land is left separating the two bends.  
•  This is eventually eroded by floods forcing the river to flow on a straight channel.
•  A loop of the meander is abandoned to form an oxbow lake.

(c) Explain ways in which lakes modify the climate of the surrounding areas.

• The lake breezes have a cooling effect on the surrounding area/warming effect on land during the cold season.
•  High rate of evaporation from the lake leads to the formation of convectional rainfall on the land.
•  Evaporation from the lakes increases moisture in the atmosphere leading to increase in humidity.
•  (Lake and land breezes help moderate the temperature of the surrounding areas).
•  These breezes may strengthen or divert the prevailing winds.
•  The lake influences the occurrence of local winds/land &lake breezes.

​(d) Give four reasons why some lakes have fresh water.

•  They are fed by rivers/have inflow which dilutes the salts.
•  The bedrocks contain mineral salt? salt minerals.
•  The bedrock do not contain saline rocks.
•  They have surface outlets which carries away salts.
• They have underground outlets which drains accumulated salts.
•  They are situated in areas of high rainfall.
•  Some are found in areas of low temperatures therefore have minimal evaporation.

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