Discuss the Global Hydrological Cycle
- The sun heats up the ocean, water is evaporated from a liquid into water vapour.
- As the water vapour rises, it cools and condenses to form clouds.
- The clouds move inland by the process of advection
- The clouds release water as precipitation and further water is added due to sublimation.
Discuss the Global Hydrological Cycle (2)
- If the precipitation falls on an impermeable surface, it will remain as surface flow.
- This water can be intercepted by vegetation absorbed and added back to the GHC by evapotranspiration
- If the precipitation falls onto a permeable surface, it will infiltrate downwards.
- The water will move its way back to an area of storage through subsurface flow or groundwater flow.
What is the Shape of Basin + Relief as a physical factor that affects hydrographs?
- Large Drainage Basins catch more precipitation, so will have a higher peak discharge which equals a longer lag time
- Small Drainage Basins generally have shorter lag times because the water doesn’t have to travel far.
- Drainage Basins with steep sides tend to have shorter lag times as the steepness of the slopes allows water to flow into the river quicker.
What is Precipitation as a physical factor that affects hydrographs?
- Heavy stems result in a higher discharge.
- The lag time is likely to be greater if the discharge is snow rather than rain, due to snow taking more time to melt.
- When the precipitation is long the land becomes waterlogged and very saturated, leading to greater surface runoff, so drainage will be fast, resulting in a shorter lag time.
What is Drainage Density as a physical factor that affects hydrographs?
- Basins the have more streams (tributaries) have a shorter lag-time.
What are Tides as a physical factor that affects hydrographs?
- High tides prevent water from entering the sea - leading to an increase in flooding, which also results in a gentle falling limb.
What is Vegetation as a physical factor that affects hydrographs?
- If the Drainage Basin has a large amount of vegetation, it slowed down the runoff due to interception, making the lag time longer.
What is Soil as a physical factor that affects hydrographs?
- Sandy Soils (with Space between particles absorb water - increasing lag time.
- Clay soils do not absorb water so runoff is quicker, decreasing lag-time.
What is Temperature as a physical factor that affects hydrographs?
- When the temperature is low, water may be stored as snow or ice, reducing runoff, and making lagtime longer.
- When the temperature, snow + ice melts, increasing runoff + decreasing lag-time.
What is Geology (Bedrock) as a physical factor that affects hydrographs?
- Rocks can be permeable (allowing water through), this slows down runoff and increases lag time.
- Rocks can be impermeable (not allowing water through) which speeds up the runoff and shortens lag time.
- Rocks can also be porous (allowing water to soak through and be stored in the rock) such as chalk, which slows runoff.
What is Climate Change as a human factor that affects hydrographs?
- It is believed that Climate Change will lead to an increase in precipitation events - leading to an increase in storms and flooding.
What are Overgrazing and Irrigation as human factors that affect hydrographs?
- Overgrazing leaves land with less vegetation, leading to increased runoff.
- When you take water from a river or the ground for irrigation, you may reduce river discharge.
What is Deforestation as a human factor that affects hydrographs?
- Deforestation is the cutting down of trees, which increases surface runoff.
- Soil Erosion may also increase where the top soil is carried into a river which reduces channel capacity for water, leading to flooding.
What is Urbanisation as a human factor that affects hydrographs?
- Urbanisation leads to an increase in impermeable building materials which increases surface runoff and leads to a shorter lag time + increase in peak discharge.
- Drainage Dishes + storm channels all increase the speed at which water enters the river channel.
What is Mining as a human factor that affects hydrographs?
- Opencast quarrying reduces vegetation cover, increasing runoff.
- With mining, there is also a change of soil erosion again being carried rivers + reducing their capacity to hold water, which leads to more flooding.
