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Geography > Lecture 7: Human influence > Flashcards

Lecture 7: Human influence Flashcards

1
Q

What is the changing human influence over the past 50-100 years?

A

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2
Q

What is the human influence index?

A

A measure of humanities influence on terrestrial ecosystems using data on human
settlements (population density, built up areas), access (roads, railroads, navigable
rivers, coastlines), landscape transformation (land use/land cover) and electric power
infrastructure (nighttime lights).

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3
Q

How do human modify the hydrological cycle?

A
  1. water withdrawals/ pumping
  2. irrigation
  3. dams
  4. climate modification
  5. pollution
  6. deforestation
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4
Q

Why do we Manage Water?

A

Mainly Because of
Water Scarcity and Climate Variability
Spatial Variability of Freshwater Resources: Annual River Flows

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5
Q

Humans have battled with climate variability and

water scarcity for 1000s of years

A

Bawdis in India used for water storage

The multiple arches
of the Pont du Gard
in Roman Gaul
(modern-day
southern France).
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6
Q

what are broad categories of modifications?

A
  1. Regulation of rivers, lakes
    and estuaries
  2. Water abstraction or release
  3. Indirect: Changes in land use,
    climate change
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7
Q

RIver lake and estuary regulation:-

Damming, building and management of reservoirs and rivers

A

reason :

Public, industrial and irrigation water supply, owing to a lack of
freshwater or water of sufficient quality.

Cooling water for power plants.

Hydropower.

Navigation/transport.

Flood control.

Low flow enhancement (for reliable downstream water supply,
for river habitat, maintain alluvial groundwater tables and
enhance flows in case of pollution events)

Fish farming and fishing.

Recreation.

River channeling (for flood control, flooding for irrigation,
drainage of surrounding land and navigation)

Building of weirs (to regulate flow and water level, improve
fish habitats, production and fishing possibilities)

Dredging of river channels (for navigation, drainag

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8
Q

River alke and estuary regulation
1. lake regulation

  1. estuary regulation
A
  1. Lake shore modification to prevent erosion, and encourage
    tourism and recreation.

Fishing.

Water storage for public supply, hydro energy and flood
defence.

  1. Estuary barrages for hydropower generation, flood defence,
    land reclamation, navigation, industrial development, water
    storage and tourism.

Upstream modifications of tidally influenced river reaches, to
control tidal effects in river and flood effects in estuary areas.

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9
Q

water abstraction or release
1. surface water abstraction/release

  1. groundwater abstraction/release
A 
1.
Public, industrial and irrigation water supply.
Recharge groundwater.
Fish farms.
Cooling water for power plant.
Generation of hydroelectric power.
Store water in reservoirs.
Inter-basin transfer.
  1. Public, industrial and irrigation water supply.
    Cooling water for power plants.
    Fish farming.
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10
Q

indirect and local activities
1. change in land use

  1. climate modification
A 
1.
Intensification of
agriculture and water
regulation.- Cultivation of crops with high water
requirements (e.g. sugar beet,
potatoes) or a dependence upon
irrigation (e.g. vegetables in arid
areas). Conversion of grassland to
arable land, drainage of wetlands crop
rotation, set-aside and soil compaction.

Land drainage- For cultivation, flood control,
urbanisation and infrastructure.

Deforestation- Owing to land cultivation, urbanisation
and tourism.

Afforestation- For the production of raw material
(pulp, paper, energy) and prevention of
erosion.

2.
Indirect/inadvertent
alteration- Climate change leads to changes in
precipitation and temperature patterns
and water resources
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11
Q

what are the types of dam?

A
  • embankment
  • arch
  • Gravity
  • Buttress
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12
Q

What are the effects (uses) of reservoirs?

A

Irrigation (i.e. food) - 30-40% of the 271 million
hectares of irrigated agricultural land worldwide rely
on dams

Water for consumption - 12% of large
dams are designated for water supply

Hydroelectricity - Approx. 20% of total global
electricity supply from hydropower

Flood control

Fishing, navigation, recreation, other uses

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13
Q

What are the negative effects of reservoirs?

A

Fragmentation of river ecosystems
• Dams disrupt the ecological connectivity of rivers (e.g. salmon and trout)
• Water storage in reservoirs and release patterns affect quantity, quality, and
timing of downstream flows (more later)

Reservoir Sedimentation
• Dams block the flow of
sediment downstream, leading
to downstream erosion of
sediments, and increased
sediment build-up in the
reservoir.
• Eventually all reservoirs
reduce in water-storage
capacity due to sedimentation
• Leads to diminished storage
capacity and decreased power
generation, reduced availability
of irrigation water for irrigation,
and ultimately end of the dam
and river…
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14
Q

what are the key negative effects of reservoirs?

A
  1. River and coastal erosion
  2. Water temperature
  3. Destruction of natural ecosystems
    • Increase in irrigated areas
    • Removal of natural flood protection areas (wetlands)
  4. Attenuation of natural floods
    • Many natural ecosystems depend on seasonal flooding from rivers.
    • Flood recession cropping is practiced extensively whereby the land is
    cultivated taking advantage of the residual soil moisture after the flood
    recedes
  5. Dam break and failure
  6. Water borne disease and vector transmission
  7. Population resettlement
  8. Greenhouse gas emissions (CO2 and methane)
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15
Q

what is an impacting dam

A

Davis Dam on the colorado river

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16
Q

How many dams are there?

A

• Reservoirs and dams have been built to benefit societies for thousands of years.
• The global number of dam constructions has increased dramatically over the past
six decades and is forecast to continue to rise, particularly in less industrialized
regions.
• More than half of the world’s rivers are regulated by large dams
• Nearly all river basins have a least one smaller dam.

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17
Q

What are the global distribution (by country) of large dams/ reservoirs? and dam type?

A

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18
Q

how do you estimate the total number of reservoirs?

A

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  • There are likely over 11 million reservoirs globally
  • Maybe 800,000 small registered dams
  • Maybe several million unregistered dams just in the US
  • Maybe 700 million very small tanks and cisterns
  • Total storage capacity of large reservoirs = ~7000 km3 (15% of annual global runoff)
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19
Q

How many small reservoirs, tanks and cisterns

A

(>700million)

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20
Q

more water evaporates from reservoirs than is consumed by humans?

A 
• Throughout the 20th
century, global water
use has increased in the
agricultural, domestic
and industrial sectors.
• Evaporation from
reservoirs has
increased at a slower
rate.
• Projections indicate that
both global water use
and evaporation will
continue to increase.
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21
Q

explain the three gorges dam?

A

Three Gorges Dam on the Chang Jiang
(Yangtze) in China is the largest, > 2 km wide,
185 m high and with a reservoir storing 39 km3

• The project cost $24 billion
• Took thirteen years to complete, from 1993 to 2006
• 18,000 MW of electricity (UK demand is about 35,000
MW)
• In 1993, this was thought to be sufficient to provide 10%
of China’s total energy needs
• With growing demand for power per capita, this has
reduced to about 3% of current demand
• The dam reached a full generating capacity of 18.2 GW
in 2010

22
Q

what are the impacts of the three gorges?

A

Human Impacts
• About 1.3 million people relocated
• 100 people died in construction
• 100,000 acres of farm land, 1,600 factories and mines, 13
cities, 140 towns, 1,352 villages were flooded by the dam
• Social impacts, unemployment, migration

Environmental Impacts
• Fragmentation or changing of ecosystems
• Loss of biodiversity
• Fish migration curtailed
• Threatened species include Yangtze river dolphin, Chinese
sturgeon and finless porpoise
• Landmarks affected include scenic deep gorges

Other
• About 1000 archaeological sites submerged
• Seismicity, landslides

Three Gorges dam is the largest of > 86,000 dams in China

23
Q

What are the contemporary and future changes in dams

A 
• In many developed
countries the
opportunities for
constructing new dams
are coming to an end,
with some dams
removal.
• In developing countries
there is still untapped
potential
• At least 3,700 major
dams, each with a
capacity of more than
1 MW, are either planned
or under construction.
• These dams are
predicted to increase the
present global
hydroelectricity capacity
by 73 % to about 1,700
GW.
24
Q

Grand Inga Hydroelectric Project in the Congo

- the largest dam in the world

A 
• It is expected to have an electricitygenerating
capacity of nearly
40,000MW
• Nearly twice as much as the Three
Gorges dam in China or 20 large
nuclear power stations
• ~40% of Africa’s electricity needs
• The $14bn (£9.5bn) Inga 3 project, the
first part of the mega-project, is being
fast-tracked by DRC government and
will span one channel of the vast river
Congo at Inga Falls.
• It involves a large dam and a 4,800MW
hydro-electric plant.
• Environmental and social impact
surveys will not be completed before
work starts…
25
Q

Land Cover/Land Use Change on the Water Cycle

A

• Land use impacts on the surface water balance and the partitioning of
precipitation into ET, surface runoff and GW flow
• Also changes in albedo (e.g. dark forest to light crops) alters the energy budget
and therefore ET
• Surface runoff and river discharge generally increase where natural vegetation
(especially forests) is cleared
• E.g. Tocantins River in Brazil showed a 25% increase in river discharge between
1960 and 1995 coincident with expanding agriculture

26
Q

what are the global changes in land use over time

A

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27
Q

Example Land Cover/Use Change: Deforestation

A

• The removal of trees (deforestation) has a major impact on the water cycle
• Trees generate a great deal of ET, which is then recycled to precipitation further
downwind.
• Deforestation therefore contributes to changes in the water cycle in other regions.

Percentage change in precipitation due to 2000–2050 business-as-usual deforestation
of the Amazon basin. a) Wet season; b) dry season. (Spracklen et al 2012)

28
Q

Deforestation Impacts on River Discharge

A

This map shows gridded fields of changes in river discharge (delta Q) due to historical
deforestation. This historical scenario compared distributed river flow (Q) generated from
pre-industrial land cover with river flow derived from contemporary landcover.

29
Q

Example Land Cover/Use Change: Urbanisation

A 
• Urbanisation increases the
amount of impermeable
surfaces, which reduces the
amount of infiltration and
percolation.
• The high drainage density
associated with the network
of drains, gutters, sewers
and flood relief channels,
quickly carries water into
river channels, thereby
increasing channel storage.
Example Land Cover/Use Change: Urbanisation
• Moreover, water quality is affected by urbanisation. Overland flow in urban areas
picks up suspended solid particulate matter and dissolved chemicals, from motor
exhausts for example, making water quality poor, and in some cases it may even
be toxic.
30
Q

Example Land Cover/Use Change: Irrigation

A

• Irrigation has increased dramatically to sate
the increasing demand for food for a
burgeoning population, and particularly in
drier regions, where rainfed agriculture is not
feasible
• Drier regions also require more irrigation
water because of the higher PET rates
• This requires withdrawing water from rivers
and groundwater, causing rivers to dry and
resources to be depleted.
• At the same time, it can cause enhanced
surface runoff and leaching of nutrients,
which leads to increased use of fertiliser, with
potential for pollution of waterways
• Another problem is that salt is brought up
from lower levels (salination).

31
Q

Irrigation as a Land Use Practice that Impacts on

Water Resources

A
  • Direct impacts on local water –increased ET
  • Potential changes in runoff and recharge
  • Indirect impacts on regional water via recycling

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32
Q

groundwater pumping

A

• The use of water-bearing rocks – aquifers – to
supply water is widespread.
• Problems: if the use of groundwater exceeds
the recharge of groundwater, the water table
drops.
• One of the main problems of groundwater
abstraction is in coastal areas, namely saltwater
intrusion. Salt-water intrusion is severe
along the Mediterranean, Black Sea and Baltic
coasts.
• Wetlands are also becoming scarce, and
many rivers are drying up, with impacts on
aquatic ecosystems, as well as economic
functions such as water supply and
navigation.
• Groundwater pollution is difficult to treat.
Groundwater is filtered slowly – sometimes
over centuries and millennia – and its
temperature and oxygen levels are lower than
surface waters.

33
Q

World’s Largest/Important Aquifers

A

Simplified version of a global groundwater resources map highlighting the locations of
regional aquifers systems

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34
Q

Global GW Recharge, Withdrawal and Depletion

Regional Groundwater Depletion

Global Groundwater Depletion over Time

How long will Groundwater Resources Last?

Anthropogenic Groundwater Recharge

A

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35
Q

Groundwater Pumping à Subsidence

A

• Land subsidence is a gradual settling or sudden sinking of the Earth’s surface owing
to subsurface movement of earth materials.
• The principal causes are aquifer-system compaction, drainage and decomposition of
organic soils, underground mining, oil and gas extraction, hydrocompaction, natural
compaction, sinkholes, and thawing permafrost (National Research Council, 1991).
• Effects include damage to buildings and roads/canals, increased flood risk in lowlying
areas, and lasting damage to groundwater aquifers and aquatic ecosystems.

36
Q

Groundwater Pumping – Subsidence in California

A

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37
Q

Trends in GW Depletion as

detected by the GRACE satellite

A

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38
Q

Case Study - Indian Groundwater Depletion

A

Among the world’s largest groundwater basins, the Indus
Basin aquifer of India and Pakistan, is a source of fresh
water for millions of people northern India, which includes
the nation’s breadbasket of wheat and rice production

Scientists have estimated that northern India is depleting
groundwater at a rate of 54 billion cubic meters per year,
a volume that could support a subsistence-level diet for
some 180 million people.

In addition to the breadbasket states of Punjab and
Haryana in the northwest, groundwater levels are falling
extensively across India in Andhra Pradesh, Gujarat,
Maharashtra, Rajasthan and Tamil Nadu.

More than 15 percent of India’s food is being produced by
mining groundwater

• The electric pump - a symbol for India’s “resourcedraining,
energy-wasting, treasury-tilting” farm policies
.
• The agriculture sector makes up 19 percent of India’s
electricity consumption, most of it to power India’s 20
million electric pumps that pull water from deep in the
ground.

• Provision of free or cheap electricity and water to
India’s poor population has led to the proliferation of
millions of electric water pumps that deplete
groundwater supplies in the fertile northern graingrowing
region.

• So much of the country’s electricity is used to power
water pumps that India’s coal-fired electrical sector and
government-owned coal mines cannot keep up with
demand

39
Q

Case Study - Indian Groundwater Depletion

A

• With 54 percent of India’s total area facing high to extremely high stress, almost 600 million people are at
higher risk of surface-water supply disruptions.
• Note, in particular, the extremely high stress area blanketing Northwest India. The region is India’s
breadbasket, producing the majority of the country’s water intensive rice and wheat stocks
• Groundwater levels are declining across India. Of the 4,000 wells showing statistically significant trends, 54
percent dropped over the past seven years, with 16 percent declining by more than 1 meter per year.
• Farmers in arid areas, or areas with irregular rainfall, depend heavily on groundwater for irrigation. The Indian
government subsidizes the farmers’ electric pumps and places no limits on the volumes of groundwater they
extract, creating a widespread pattern of excessive water use and strained electrical grids.
• Northwestern India again stands out as highly vulnerable. Of the 550 wells studied in the region, 58 percent
have declining groundwater levels.

40
Q

Upstream - Downstream Effects

and links to competition and conflict

A 
The discharge of many large rivers has
indisputably been affected by water
management, especially dam construction
- but also within-basin diversions for other
beneficial uses such as irrigation and
municipal and industrial water supply,
trans-basin diversions, land use, …
41
Q

Changes in Discharge in Major Global Rivers

A

Since construction of the High Aswan Dam almost all the
Nile River’s discharge is now either diverted for irrigation or
lost to reservoir evaporation.

Flows of the Syr Darya River have declined greatly because
of irrigation diversions upstream (one of the major
tributaries of the Aral Sea).

In contrast, the flow of the Burntwood River increased by a
factor of four following an upstream diversion into the river
basin in the 1970s for hydro- power production.

Observed flow of the Columbia River after construction of large reservoirs, as well as
‘naturalized’ discharge and projected effects of climate change on the naturalized
flows by 2050

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42
Q

Examples of hydrologic interactions in river

basins – upstream-downstream impacts

A

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43
Q

Concepts of River Fragmentation and River Regulation

A

• Two of the largest consequences of dam construction (and other
management) are river fragmentation and river regulation.

  • These can be represented by the
  • River Fragmentation Index (RFI) and
  • River Regulation Index (RRI)
  • Quantifying these types of indices is useful in characterizing effects on
  • water resources
  • biodiversity,
  • ecosystem functioning, and
  • fluvial geomorphology
44
Q

River Fragmentation Index (RFI)

A

• A measure of river fragmentation by barriers on structural connectivity per basin
and is defined as the volume of flow separated by the barrier.

• Where Qannual,ds is the annual discharge downstream of the dam and Qannual is
the annual discharge for the whole basin

• The RFI of an unfragmented river network is 0%, with each subsequent dam
increasing the value to a maximum of 100%.

• A single dam in a previously undisturbed network leads to greatest
fragmentation if it splits the network into two equal volume fragments, in which
case the RFI increases to 50%.

45
Q

River Regulation Index (RRI) and

Degree of Regulation (DOR)

A

• The DOR is the proportion of a river’s annual flow volume that can be withheld
by a reservoir or a cluster of reservoirs upstream of the reach and is calculated
for each reach of the network.

• Where C is the capacity of the reservoir (km3) and Qannual is the annual flow of
the river (km3)

• A high DOR indicates an increased probability that substantial discharge
volumes can be stored upstream in a given year for future release.

• The RRI is an extension of the degree of regulation (DOR) and provides a
quantitative proxy of how strongly a river may be affected by alterations to its
natural flow regime due to upstream dam operations.

• RRI (%) is calculated by first weighting the DOR value of each individual reach
with its corresponding river volume, and then averaging the results for the
entire basin to quantify full-basin impacts in a single index.

46
Q
  1. Degree of Regulation (DOR)
A

The degree of regulation is the ratio between total upstream storage capacity and the
annual average discharge of a river reach. DOR can be used as an indicator of impact
on downstream flows

47
Q

Combining the RFI and RRI

A

We can combine the RFI and RRI to see the global picture of impacts of dams
• Green indicates basins with low fragmentation and low regulation
• Blue indicates basins with low fragmentation but severe regulation
• Yellow indicates basins with severe fragmentation but low regulation
• Red indicates basins with severe fragmentation and severe regulation

*48% of river volume is moderately to severely impacted by either flow regulation,
fragmentation, or both. Assuming completion of all dams planned and under
construction in our future scenario, this number would nearly double to 93%, largely
due to major dam construction in the Amazon Basin.

48
Q

How to Quantify and Understand the Impact of

Human Activities on Water Resources

A
  1. Carry out experiments using hydrological models with and without water
    management
  2. Carry out experiments using climate models (regional) using different land covers
  3. Impacts can also be detected by looking at river flows pre and post change
49
Q

water storage in califronia?

A

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50
Q

Impact of Water Management on Recent California Drought –

Modeling Study with and without Human Management

A 
CD5 covers the Central
Valley which is heavily
irrigated. So, human
management has a large
influence on river flows
and drought.

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51
Q

Impact of Water Consumption on Hydrological Drought Globally

A

Comparison of standardized deficit volumes with (left) pristine condition and with (middle)
transient human water consumption, and (right) relative contribution of human water
consumption (%) for major drought events over (a)–(c) North America (2002), (d)–(f) Europe
(2003), and (g)–(i) Asia (2001).

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