Topic 5 - EQ2 - Water (Miss M)

Question 1

What is the definition of a drought?

Answer 1

A deficiency of moisture that results in adverse impacts over a sizeable area over an extended period

Question 2

What are the 3 types of drought? What is sometimes considered the 4th?

Answer 2

• Meteorological drought (degree of dryness compared to normal precipitation)
• Agricultural drought (insufficient water for crops, so that they wilt without irrigation)
• Hydrological drought (where drainage basins suffer shortfalls)

Extra: Famine drought (widespread food shortages due to widespread agricultural failure)

Question 3

What are the 3 physical causes of drought?

Answer 3

• Inter Tropical Convergence zone movements (and failure of ITCZ)
• Blocking high pressure (anticyclones) in mid latitudes
• El Niño Southern Oscillation cycles (El Niño and La Niña) / Global Atmospheric Circulation

Question 4

What does high pressure bring?

Answer 4

Much less cloud coverage, less (or no) precipitation and higher than average temperatures

Question 5

What does low pressure bring?

Answer 5

More clouds, more precipitation and lower temperatures, as the low pressure air draws moisture from the ground

Question 6

What is the sub tropical high pressure band?

Answer 6

A high pressure band of air around the tropics where air that has risen at the equator cools and sinks (descending part of Hadley cell) creating a high pressure belt just below the tropics and a hot and dry climate prone to drought.

Question 7

What is the weather like at the Inter Tropical Convergence Zone?

Answer 7

The weather found at the ITCZ is persistently hot and very wet. The winds of the Northern and Southern Hemispheres come together here, this leads to the development of frequent thunderstorms and heavy rain.

Question 8

What happens to the ITCZ over the year?

Answer 8

The ITCZ moves North and South of the equator over the year, when the ITCZ is North (June to August), the Northern tropics experience a wet season whilst Southern Tropics experience a dry season, the seasons flip when the ITCZ moves South of the equator (in December to February).

Question 9

Why can the ITCZ rains fail? What happens when the ITCZ rains fail?

Answer 9

ITCZ rains may fail as the subtropical high pressure zone from the descending part of the Hadley cell blocks the air masses associated with the ITCZ.

The modification of the pattern by this blockage therefore causes rain to fail and often a drought.

Question 10

What directs depressions from west to east in mid-latitudes?

Answer 10

The polar front jet stream

Question 11

What happens when the loops of the polar jet front stream stabilise?

Answer 11

High-pressure areas, aka anticyclones, from the subtropics are enabled to move northwards bringing stable weather and very little precipitation causing mid-latitude droughts (e.g. in the UK)

Question 12

What are the normal conditions in the Eastern Pacific?

Answer 12

Normal conditions in the Eastern Pacific (South America) are dry caused by high pressure, and in the area, deep cold water rises to replace warm water keeping the water cool

Question 13

What are normal conditions in the Western Pacific?

Answer 13

Normal conditions in the Western Pacific (Australia) are warm, so is the water, as trade winds move warm surface waters westwards towards Eastern Australia, warm moist air rises, cools and condenses causing rain in this area

Question 14

What are the changes caused by El Niño every 2-7 years?

Answer 14

Warm water normally located in the Western Pacific moves eastwards towards Eastern South America when the pushing forces, keeping the warm water in the West, weaken. These warmer waters in the Eastern Pacific cause increased rainfall and flooding in South America, however, in the Western Pacific sinking air causes dry conditions and drought.

Question 15

What are the changes caused by La Niña every 2-7 years?

Answer 15

The warm water of the Western Pacific is pushed further westwards by very strong trade winds. This causes even warmer water on the Eastern coast of Australia which causes increased evaporation which leads to heavy rain and flooding. Whilst in the East there is unusually high pressure causing very dry weather, drought and very cold water.

Question 16

Do the ENSO cycles only affect the Pacific exclusively?

Answer 16

No. ENSO causes changes in global atmospheric circulation creating droughts and flooding in different areas of the world due to the inter-connectivity of the world’s different weather systems. E.g. The East African drought of 2011 was attributed to a strong La Niña.

Question 17

Do human factors cause drought or not?

Answer 17

Human factors (the vast majority of the time) do not cause droughts but rather they act like a positive feedback loop enhancing its impacts

Question 18

What are the 8 human ‘causes’ of drought? (Especially in Sahel)

Answer 18

• Over-abstraction of water from rivers and groundwater
• Building reservoirs and water transfers reducing the downstream supply of water
• Deforestation and overgrazing (by nomadic tribes in Sahel) reduces vegetation cover, reducing e/t rates and thus reducing atmospheric moisture, soil moisture and precipitation
• Rapidly increasing population partly because of better healthcare lowering death rates (Niger set to see its population double in next 20 years)
• War (or anything else blocking access to water), e.g. Ethiopian-Eritrean war
• Rural poverty
• Rain fed agriculture
• Global warming (less reliable rains)

Question 19

What is the natural function of a wetland ecosystem?

Answer 19

• Provides habitat
• Absorbs excess water from rainfall or runoff and releases it back slowly into waterways (controlling flooding)
• Absorb storm surges
• Natural water purification (plants absorb excess nitrogen and other pollutants)

Question 20

What do droughts do to wetlands?

Answer 20

Degrade and deteriorate wetlands

• Water table falls and reduced water storage
• Open water shrinks or dries up (loss of habitat)
• Extended drying can cause soil erosion
• Gaps in food webs as species die out, others prevail

Question 21

What are the two types of wetlands? Which are more resistant?

Answer 21

• River-fed wetlands experience greater water level fluctuation so the entire ecosystem is more adapted to less water
• Groundwater-fed wetlands experience a smaller range of water levels so are less resilient in droughts and more vulnerable to prolonged drought

Question 22

What is the natural function of a forest ecosystem?

Answer 22

• Water storage and regulation of hydrological cycle
• Timber production
• Carbon sequestration (forests store a lot of carbon)
• Air purification
• Wildlife habitat

Question 23

Are forests resilient to drought?

Answer 23

No.

• Trees take an average of 2 to 4 years to recover and resume normal growth rates after a drought
• Trees experience vascular issues impairing water transport
• Forest fires are common (dried out vegetation and dry soil and lower water table reducing natural protection to forest fires.
• Foliage loss
• Increased accumulation of pests and diseases (Beetle arrack on Piñon pines in California led to 90% of Piñons dying)

Question 24

What are the three big meteorological causes of flood we have studied? What regions do they apply to?

Answer 24

• Jet stream and low pressure weather (UK)
• Monsoons (India and SE Asia)
• Ice melt (Siberia)

Question 25

How does the jet stream and low pressure weather cause flooding in mid latitudes?

Answer 25

The jet stream is formed at mid latitudes between polar and tropical air masses, the jet stream brings low pressure weather (frontal rain). The passage of rain-bearing low-pressure systems or depressions brings prolonged heavy rain causing flooding. Degree of flooding depends on the depression sequence, and whether there is a cumulative effect from a previous storm.

Question 26

How do monsoons cause flooding?

Answer 26

Monsoonal rainfall can result in widespread, damaging flooding, this is because monsoon season brings around 70% of the average annual rainfall in approximately 100 days. Highest flooding risk are along river courses, river deltas and low lying plains (80% of Bangladeshi population lives in these regions).

Question 27

How does ice melt cause flooding in the interiors of Asia and America?

Answer 27

Snow and ice melts in the late spring causing extensive flooding. The great north-flowing Siberian rivers cause vast annual flooding in the plains of Siberia. The quick transition from winter to spring upstream causes rapid snow melting, while their lower reaches remain frozen, with very limited infiltration occurring causing a build up of meltwater on the surface. Often worse when rain falls in late spring too.

Question 28

What storm triggered the 2015 Cumbria floods?

Answer 28

Storm Desmond

Question 29

Before 2015 when did Cumbria see flooding of a similar magnitude?

Answer 29

2009

Question 30

What role did the jet stream have in the 2015 Cumbrian floods?

Answer 30

The jet stream (the band of fast moving air) moves north and south, but it remained over the NW for longer than normal, this brought low pressure (rain-laden depressions) across the Atlantic to Cumbria.

Question 31

What type of pressure from the Atlantic caused the 2015 Cumbrian floods?

Answer 31

Very low pressure and its fronts brought prolonged and heavy rains

Question 32

What role did Cumbria’s topography have in the floods?

Answer 32

The Cumbrian fells created Orographic (relief) rainfall as the warm moist Atlantic air was forced to rise and condense causing rain. Steep slopes also helped water run very rapidly into the rivers.

Question 33

What two types of rainfall caused the rainfall we saw in Cumbria in 2015

Answer 33

Orographic (because of Cumbrian topography) and frontal rainfall (low pressure)

Question 34

What were the antecedent conditions of the 2015 floods in Cumbria?

Answer 34

• Already saturated ground conditions (one of the wettest November’s on record in NW), there was so much rain that the already saturated ground had little space for infiltration causing overland flow pretty quickly
• Rivers Derwent and Cocker were already swollen with previous rainfall

Question 35

Exactly how heavy was the rain in Cumbria in 2015?

Answer 35

• More than a month’s rainfall in one day
• Moist air masses stayed above Cumbria for up to 48 hours
• Record rainfall

Question 36

What were the 4 main meteorological/physical causes of the 2015 Cumbrian floods?

Answer 36

• Position of Jet stream
• Low pressure system
• Orographic rainfall
• Antecedent conditions and rainfall intensity

Question 37

What were the environmental impacts of the flooding in Cumbria in 2015?

Answer 37

• Large amounts of the fragile upland soils has been washed into the swollen streams, rivers and lakes and will have an impact on water quality and aquatic wildlife.
• Millions of tons of sediment was transported by the river and deposited on floodplains and in settlements.
• Thousands of trees which once lined rivers in the area affected were ripped from river banks.
• Landslides occurred in many places as the result of heavy rainfall and the land becoming saturated.

Question 38

What were the human impacts of the flooding in Cumbria in 2015?

Answer 38

• 2 deaths
• 5,200 homes affected
• Widespread travel disruption
• Aprrox. 40 school closures
• Disruption to NHS in Cumbria
• Economic losses from Storm Desmond and Eva was estimated between £1.6 to 2.3 billion
• Gov’t provided Cumbria and Lancashire county councils £50 million to make affected households more flood resistant

Question 39

What were the human (secondary) causes of the floods in Cumbria in 2015?

Answer 39

• Impermeable surface building like roofs, pavements, roads and car parks
• Impeding channel flow by building alongside rivers (e.g. bridge supports)
• Straightening of historically meandering channels to increase flow causing flooding downstream
• Deforestation (natural woodlands intercept rain, transpire moisture and tree roots help infiltration)
• Pasture and ploughed do not allow infiltration in the same way natural grassland does

Question 40

What is the impact of climate change of inputs into drainage basin hydrological cycles?

Answer 40

• Increasing average air temperatures = decreased snow, permafrost and ice coverage and so more meltwater and initially more flooding
• Increasing average sea temperatures = increased condensation and cloud cover, increased precipitation in mid latitudes and low pressure regions of tropics but also increased high pressure systems increasing incidence and severity of drought

Question 41

What is the impact of climate change on outputs of drainage basin hydrological cycles?

Answer 41

Lead to greater outputs as greater initial evapotranspiration due to warmer air temperatures.

Question 42

How may climate change affect the Sahel desert?

Answer 42

Rains might fail with climate change if the tropical regions warm up. The ITCZ wont migrate as far north and the ‘summer’ rains will fail.

Question 43

How may climate change affect California?

Answer 43

Increasingly falling precipitation levels and increased evaporation:

• Droughts leading to more wildfires (3x normal in Sierra Nevada)
• 30 year long mega droughts 50% chance of hitting SW California, 90% chance of decade long drought
• Reservoir levels falling
• Snowpack levels falling
• Forested areas reverting to scrub and grassland

Question 44

Is there uncertainty about the impact of climate change on the water system (why?)

Answer 44

Precipitation will become more variable with increased risks of droughts and floods at different times and places. Ultimately climates will become more extreme and more extreme weather leading to flooding or droughts will be more commonplace for some areas of the world.

Question 45

How is uncertainty impacting on water security and supplies?

Answer 45

With a change in precipitation, temperature and potential E/T the severity and occurrence of droughts will rise too (meaning water security is declining).

Question 46

How will droughts create uncertainties in the future?

Answer 46

Droughts create an uncertain future in terms of water security. Droughts do not only mean that people in affected regions need to prepare to have less water in the future for drinking or households, but droughts can also lead to other big issues like crop failure and forest fires which can devastate regions more than a lack of water for households.