5.7 climate change and the hydrological cycle

Question 1

How does climate change vary the hydrological system

Answer 1

Increased greenhouse gases in the atmosphere

Increased climate change

Surface heating of sea and land surfaces

Increased temps around the world
Increase in evaporation, possibly leading to drought

Increase in atmospheric water holding capacity
Increase in actual moisture content in the atmosphere

Enhanced precipitation rates and latent heating

Enhanced storm intensity

Increased run off and flooding and change in precipitation patterns. This varies differently around the world

Question 2

How does climate change influence evaporation?

Answer 2

In Asia and North America, evaporation is increasing, but increased cloud cover from increased water vapour may work against this

Question 3

How does climate change influence transpiration?

Answer 3

Transpiration rates are subject to vegetation changes, soil moisture and precipitation
Transpiration increases exponentially as vegetation becomes more productive

Question 4

How is soil moisture influenced by climate change?

Answer 4

Ambiguous results as it’s linked to many factors:
Where precipitation increases, so does soil moisture, but where evaporation increases, soil becomes drier

Question 5

How is run-off and steam flow affected by climate change?

Answer 5

A 1 degree rise in temperature could increase global run off by 40%
Along with more climate extremes, there will be more hydrological extremes, with more low flows (droughts) and high flows (floods)
An accelerated cycle with more intense rainfall will increase run off rates and reduce infiltration
This has been shown by a clear decrease of run off in continental Mediterranean , Africa and south western US

Question 6

How does climate change influence groundwater flow?

Answer 6

no clear evidence what climate change will do as human abstraction is a dominant influence

Question 7

How is reservoir, lake and wetland storage influenced by climate change?

Answer 7

Wetlands are affected when there is decreasing water volumes and higher temperatures
Changes to wetlands are occurring but they are not conclusively due to climate change.

Regional variations in lakes and reservoirs have been linked to regional changes in climate, for example, Lake Chad

Question 8

How does climate change influence permafrost?

Answer 8

Higher temperatures at higher latitudes lead to permafrost degradation
With the deepening of the active layer, this has an impact on ground water supplies and releases methane from thaw lakes, accelerating change

Question 9

How does climate change influence snow?

Answer 9

Length of snow cover season has decreased and spring melt has occurred earlier, accelerating in the last decade

Question 10

How does climate change influence ice?

Answer 10

Glaciers have retreated globally since the end of the Little Ice Age with downwasting (thinning of glacier due to melting of ice) accelerating in most areas since 1970.
High altitude glaciers have shown the most rapid melt, leading to low flows from a dwindling cryosphere

Question 11

How does climate change influence oceans?

Answer 11

Warmer oceans leads to more evaporation and greater volume, but evidence is lacking

Question 12

How does climate change influence precipitation input?

Answer 12

There is likely to be an important change in the type of precipitation, given more now falls as rain rather than snow.
There is widespread increases in intense rainfall but the overall amount of water remains the same.
Precipitation increases in the tropics and high latitudes, but there’s decreases 10-30 degrees north and south of the equator
However, between 10-30, intensity of heat waves has increased, leading to drought

Question 13

What are some of the elements of the hydrological cycle that climate change will impact?

Answer 13

Precipitation input
Evaporation
Evapotranspiration
Soil moisture
Run-off and steam flow
Groundwater flow
Reservoir, lake and wetland storage
Permafrost
Snow
Ice
Oceans

Question 14

What are the impacts of short term climate change on water supply, diminishing water supply and increasing uncertainty?

Answer 14

More frequent cyclone and drought events
Depleted aquifers
Decreasing rainfall in many areas
Greater rates of evapotranspiration from surface water in summer
Increased intensity and frequency of drought
ENSO is creating more unreliable patterns of rainfall
Loss of snow and glaciers threaten many mountainous communities

Question 15

What is the normal state of the atmosphere when analyzing the ENSO cycle?

Answer 15

In normal years, Pacific winds circulate around the Walker cell. Wind travels westward, taking warm surface water with them. As it flows west, it’s heated by the sun. Warm, moist air rises over Indonesia, creating a low-pressure area and heavy rain. The air then circulates east in the upper atmosphere, sinking into the cooler, high-pressure area over Southern America, giving it dry conditions and creating the Atacama Desert.

Question 16

What is the normal state of the water when analyzing the ENSO cycle?

Answer 16

Water is taken west as its moved by trade winds towards the coast of Australia and Indonesia. Then, the warm water sinks at the coast of Australia, moves back east by thermocline, below the warm water moving west and then rises again by the coast of South America to replace the warm water in upwelling

Question 17

How does the atmosphere circulate in La Nina

Answer 17

When the normal situation intensifies. Low pressure over the western Pacific becomes lower and high pressure over the Eastern Pacific becomes higher. As a result, rainfall increases over Southeast Asia and South America suffers drought. Trade winds strengthen due to increased pressure difference between the two areas

Question 18

What is the atmosphere like during El nino?

Answer 18

During this, pressure systems and weather patterns reverse. Warmer waters develop in the eastern Pacific, causing lower pressure and hence drawing in westerly winds from the Pacific. Warm, moist air rises, creating heavy rainfall over the Eastern Pacific. The air then circulates west in the upper atmosphere. The descending air then creates drier conditions which lead to drought in Australia and Indonesia.

Question 19

When were there strong El nino events?

Answer 19

97-98 and 2015-16

Question 20

When were there strong la nina events?

Answer 20

07-08 and 2010-11

Question 21

How will climate change impact ENSO?

Answer 21

Climate change could increase their duration and intensity, meaning regions bordering the Pacific will see flood seasons following drought seasons. This will affect future water security

Question 22

Unless carbon emissions are significantly reduced, what will happen to precipitation patterns in the UK?

Answer 22

The risk of winter flooding in the UK is predicted to increase by four times, and the risk of summer drought by three times

Question 23

What are the two case studies for climate change and the hydrological cycle?

Answer 23

Example of good things occurring due to climate change - The Sahel
Example of bad things happening due to climate change- California

Question 24

What is the level of rainfall like in the Sahel annually?

Answer 24

Rainfall varies from 100mm to 600mm per year

Question 25

What was precipitation like in the 1970s and 180s in the Sahel and what were the effects of this?

Answer 25

In a normal year, 90% of its annual rainfall would fall between July and September, as part of the West African Monsoon. However, these rains failed in the 70s and 80s- with a decline of up to 40% between the 50s and 80s.
Drought, poverty and civil war, especially in Ethiopia and Eritrea, drove many people onto marginal land and many died in famine

Question 26

How has precipitation in the Sahel in recent years shown hope?

Answer 26

Since 1996, there have been several wet years in between the droughts, pointing to an opportunity for re-greening, which is the conversion of dry landscapes to productive farmland.

Question 27

What does re-greening involve in the Sahel and where is it popular?

Answer 27

It involves planting trees and bushes, alongside other sustainable land management schemes. It’s popular in Malawi, Burkina Faso, Ethiopia and Niger, where hundreds of farmers benefit from increasing yields

Question 28

What are the benefits of re-greening?

Answer 28

-Natural regeneration of water-retaining shrubs and trees
-low cost reforesting
-the use of water harvesting techniques. For example, Burkina Faso’s farmers build stone lines or dig improved planting pits to trap limited rainfall on fields and increase yields.

Question 29

How many Californians are affected by problems caused by variations in rainfall?

Answer 29

40 million

Question 30

What happened to the number of wildfires in the Sierra Nevada region in 2014, because of unusually high levels of drought?

Answer 30

It experienced three times the normal number of wildfires, because the ground was so dry

Question 31

What is a mega-drought?

Answer 31

a period of unusually low rainfall lasting for decades or longer

Question 32

What happened in 2015 in California in terms of drought?

Answer 32

This marked the 4th year of continuous drought in California- the worst in 1,200 years- and water rationing was imposed on cities

Question 33

What do forecasts now suggest the likelihood of a mega drought or decade long drought is in California?

Answer 33

there is a 50% chance of mega-droughts and 90% of a decade long drought

Question 34

How many of the years between 2000 and 2015 have been drought years and how many people is this affecting?

Answer 34

Eleven of these years
This affects people in California, Nevada, Texas and more, affecting a population equal to the UK

Question 35

What are the causes of droughts in California?

Answer 35

-rising temperatures leading to increased evaporation rates
-a fall in precipitation

Question 36

How has surface run off and soil moisture levels been affected in California?

Answer 36

Declined

Question 37

How has land use changed in California due to climate change?

Answer 37

-forested areas reverting to scrub and grasslands

Question 38

How has groundwater been affected in California?

Answer 38

Groundwater levels fell by 30m between 2011 and 2015. These are used to supply las Vegas and Los Angeles to make up for the shortfall in rain

Question 39

How has reservoir levels been affected in California?

Answer 39

Reservoir levels have fallen. In October 2016, water storage was 77% of the average for that time of year. Lake Cachuma was down to 9%.

Question 40

How has snowpack been affected in California?

Answer 40

In 2015, snowpack levels were at record lows due to high temperatures and a lack of winter storms. Snow pack is crucial because its meltwater provides 1/3rd of water used by California’s cities and farms