1.4 The human impact Flashcards
What are the urbanising influences?
- Removal of trees and vegetation
- Initial construction of houses, streets and culverts
- Complete development of residential, commercial and industrial areas
- Construction of storm drains and channel improvements
What is the possible hydrological response to removal of vegetation?
- Decreased evapotranspiration and interception
- Increased stream sedimentation
What is the possible hydrological response to Initial construction of houses, streets and culverts?
- Decreased infiltration and lowered groundwater table
- Increased storm flows and decreased base flows during dry periods
What is the possible hydrological response to development of residential, commercial and industrial areas?
- Decreased porosity, reducing time runoff concentration thereby increasing peak discharges and reduced time lag
- Increased volume of runoff and flood damage potential
What is the possible hydrological response to construction of storm drains and channel improvements?
- Local relief from flooding
- Concentration of floodwaters may aggravate flood problems downstream
Human impact on precipitation
- Cloud seeding
- As rain requires particles such as dust and ice on which to form, seeding produces silver iodide, solid CO2 (dry ice) or ammonium nitrate to attract water droplets
=> increase precipitation
Dams’ effects on hydrological cycle
- Impoundment of water behind the dam causes the velocity of water to drop => increase potential for evaporation from the river => increased precipitation => soil will be saturated => little infiltration and percolation
- Volumes of channels increase, might exceed peak discharge => increased surface runoff => little baseflow, throughflow and groundwater flow
- An increase in precipitation means that water will be absorbed by plant => increased evapotranspiration
Urbanisation’s effects on hydrological cycle
Overall:
- an increase in surface runoff
- reduction in evapotranspiration
- decline of surface storage (puddles)
- increased lag time
What are the effects of extracting groundwater?
- Surface water flooding
- Pollution of surface waters and spread of underground pollution
- Flooding of basemets
- Increased leakage into tunnels
Define flood
A high flow of water which overtops the bank of a river. Occurs when the river’s discharge exceeds the capacity of its channel to carry that discharge
Physical causes of flood
- Excessive level of precipitation occurring over a long period of time
- Intensive precipitation over a short period of time
- Snow melt
- Climatic hazards such as cyclones and storms
- The nature of the drainage basin - relief, soil type, shape, vegetation
Human causes of flood
- Urbanisation - construction of concrete buildings and roads => increases impermeability of surface => increased overland flow
- Deforestation => less interception => more groundwater flow and overland flow
- Climate change/ global warming => ice melt
- River management on 1 part of the drainage basin that increases flood risk in other areas - dam
Define recurrence interval
Refers to the regularity of a flood of a given size. Small floods may be expected to occur regularly. Larger floods occur less often
How to improve flood warnings?
- Improved rainfall and snowpack estimates, better and longer forecasts of rainfall
- Better gauging of rivers, collection of meteorological info and mapping of channels
- Better and current info about human populations, infrastructure, elevation and stream channels to improve flood risk assessment models
- Share info to the general public
Define disaster aid
Refers to any aid such as money, equipment, staff and technical assistance that is given to a community following a disaster
Define loss sharing
Adjustments including disaster aid and insurance
Define event modification
Adjustments including environmental control and hazard-resistant design
How well a flood is dealt depends on:
- The level of preparedness at the location of the expected hazard
- Amount of warning
- Level of economic development
Define flood management
- Seeks to reduce the frequency and magnitude of flooding and therefore, limit the damage a flood causes
- Can be achieved by 2 methods: hard and soft engineering
Define hard engineering
Controlled disruption of natural processes by using man-made structures. Has the most definite outcome. Occurs where flood protection is vital. e.g. dam construction
Define soft engineering
Uses natural processes and natural systems to slow down and store water. Not as well developed, therefore outcomes occasionally uncertain. e.g. afforestation
Define drought
An extended period of dry weather leading to conditions of extreme dryness
Causes of drought
- Due to global atmospheric circulation around 20-30 degrees N and S (subtropical high pressure belt)
- Distance from sea and continentality
- Rain shadow effects
- Human activities such as cash crop farming, overgrazing, slash and burn gives a rise in desertification
Effects of drought
- Hunger and malnutrition
- Declining crop yields
- Reduced water supplies
- Stress on natural ecosystems
- Economic activities may be affected
Methods of preventing and lessening drought
- Public education and education campaigns
- Water service restrictions
- Improvements in water systems
- Management of available water resources
