5.2 drainage basin

Question 1

3 types of rainfall

Answer 1

1. convectional rainfall (most common)
   INNER TROPICAL CONVERGENT ZONE
   sun heats the land and air above, warm air rises, cools &condenses forming clouds, rain then occurs (‘heavy rain’)
2. orographic (relief) rainfall
   eg THE LAKES (western side of UK), Andes rain shadow effect.
   warm moist air is forced to rise over high areas, meets the cold mountain air, cools and condenses forming clouds and it rains. can lead to flash flooding
   !!one side of the mountain is slightly drier due to rain shadow effect!!
3. frontal rainfall
   occurs when particularly cold and particularly warm air mass interact (called a depression!!! 100 hit the UK a yr on avg.) warm air forced to rise over cold air, air cools and condenses as it rises forming clouds and rain… creates cyclonic precipitation

Question 2

distribution of rainfall

Answer 2

• most precipitation occurs in the ITCZ (inter- tropical convergence zone) which is a band of intense low pressure which leads to precipitation.it changes with the seasons, moving north in summer & south in winter!
• ocean temperatures: warmer oceans mean warm air evaporates from oceans more rapidly creating more intense rainfalls.
• intense band of sun along equator creates this persistant band of rainfall which then contributes to conditions of ITCZ

Question 3

how do inputs in a drainage basin vary?

Answer 3

main input= precipitation, different chracteristics can have a significant effect on the drainage cycle.
1. form: rain, snow or hail (snow= temporary store followed by sudden flux following thawing and high discharge)
2. intensity (difficult for rain to inflitritrate if it is intense= more overland flows)
4. seasonality (drainage basin operates at diff flow levels at diff times of yr, eg monsoon seasons)
5. distribution (significant in large drainage basins eg Nile where tributaries start in different climates)

Question 4

2b) types of fluxes/ flows in a drainage basin

Answer 4

1. interception/ infiltration (retention of water by plants and soils: high vegetation cover increases infiltration rates: more porous fue to root networks)
2. percolation (deeper transfer of water into permeable rocks)
3. through flow
4. groundwater flow
5. surface runoff (increased through steep slope angles, duration of rainfall)

Question 5

2b) how do outputs in a drainage basin vary? (types)

Answer 5

1. evaporation
2. transpiration
3. discharge

Question 6

impact of physical factors on drainage basin

Answer 6

1. climate (mainly impacts inputs and outputs: type and amount of rain and amount of evaporation, also impacts vegetation type)
2. soils (mainly affects flows, ie surface runoff: amount of infiltration and through flow)
3. geology (impacts subsurface flows ie percolation and groundwater flows: therfore aquifers, also surface runoff and indirectly, soil formation)
4. relief (mainly impacts flows, also amount of precipitation and slopes impact amount of runoff)
5. vegetation (mainly impacts flows, presence/ absence of veg has major imoact on amount of interception, infiltrayion and occurance of overland flow as well as transpiration rates)

Question 7

2c) impact of human factors

Answer 7

1. over abstraction= declining groundwater storage
2. deforestation= reduction in evapotranspiration and increases surface run off, soils lose quality and can become quickly compacted by rain. (little soaks into the ground, level of groundwater is depressed, risk of rivers running dry when the rain stops)
3. agriculture a) pastoral= compaction of soil from livestock increasing surface run off
   b) arable= ploughing increases infiltration
4. urbanisation= increased surface run off and reduction in infiltration and percolation, drains deliever rainfall quicker to rivers (shorter lag time) increasing flood risk