Lecture 13 - A World of Changing Environments Flashcards
What is the Definition of Hydrology?
-The branch of science concerned with the properties of the Earth’s water and especially its movement in relation with the land (Oxford English Dictionary)
How is the World’s Freshwater Distributed?
-0.3% in rivers, lakes and wetlands
-69.2% in ice sheets, glaciers and permafrost (cryosphere)
-30.4% in groundwater
-0.1% in the atmosphere and biosphere combined
Why do Temperate Latitudes experience Higher Rainfall?
-Net solar radiation is lower here so there is less likelihood of evaporation
-Precipitation is greater than evaporation
-These areas are the bread-baskets of the world
Describe India’s Water Stress
54%of India faces high/ extremely high water stress
-NASA found that large-scale irrigation caused 108 cubic kilometres of groundwater loss in Haryana, Punjab, Rajasthan and Delhi between 2002-2008
-In July 2012, half on India’s population (around 670 million) temporarily lost power following a grid failure
-This was thought to have been caused by severe drought in Northern India which reduced HEP output
What is Catchment-Scale Hydrology?
-A fundamental unit (ie. a drainage basement)
-Input = precipitation and influent groundwater flow
-Output = river flow, evapotranspiration and effluent groundwater flow
-Flooding = input>output
-River flow/ discharge = Q
-Rain is either intercepted, infiltrates, run-off or transpired
What are the 2 Types of Runoff?
-Hortonian = where rainfall intensity exceeds infiltration rate in the soil
-Saturation = ground gets saturated causing the groundwater table to rise and can’t absorb anymore water leading to overland flow (runoff)
What are the Components of a Hydrograph?
-Base flow = river fed by groundwater
-Rising limb = increase in stream discharge before peak discharge
-Peak flow = peak discharge (Q)of the river
-Falling limb = decrease in discharge after peak discharge
-Base time = time taken to return to base flow
-Lag time = time between peaks of precipitation and peak discharge
How does Vegetation influence the Discharge of a River?
-Interception means leaves and branches slow the flow of water to the ground
-Transpiration takes water from the ground and releases it back into the atmosphere as vapour
-Organic matter from decaying vegetation improves the soil structure and infiltration capacity
How does Infiltration Capacity influence the Discharge of a River?
-Open, well-structured organic-rich soils promote infiltration
-Soil compaction and surface-crushing promotes runoff
-Urban areas are covered in impermeable surfaces; 100% runoff; shorter lag time; increased flood risk
-Prior rainfall to a storm event means the ground is saturated which results in storm flow (shorter lag time)
How does Surface Storage influence the Discharge of a River?
-Natural depressions in catchments such as pits and mounds can store water temporarily
-They act as storage, lengthen the lag time and delay flood peaks
Describe the Changes in Rainfall for Spring and Summer in the UK from 1961-2006
-Annual mean precipitation over England and Wales has not changed significantly since records began (1766)
-Seasonal rainfall is highly variable, but appears to have decreased in summer periods
-In summer, all region except NE England and N Scotland show decreases in rainfall
Describe the Changes in Rainfall for Autumn and Winter in the UK from 1961-2006
-All regions of the UK have experienced an increase over the past 45 years in the contribution to winter rainfall from heavy precipitation events
