Enquiry question 2: What factors influence the hydrological system over short- and long-term - PowerPoint Presentation

Enquiry question 2: What factors influence the hydrological system over short- and long-term timescales?

EQ1 : What are the processes operating within the hydrological cycle from global to local scale EQ2: what factors influence the hydrological system over short- and long-term timescales?EQ3: How does water insecurity occur and why is it becoming such a global issue for the 21st century? Area of study 3: Physical Systems and SustainabilityTopic 5: The Water Cycle and Water Insecurity

Today we are learning this content: 5.4 ( a )

The causes of drought Aims: To be able to explain the physical causes of drought To suggest the impact human activity has on the drought riskTo explain how drought impacts ecosystem functioning

What is drought? The UN provides a definition of drought as ‘drought is defined as an extended period - a season, year, or several years of deficient rainfall relative to the statistical multi year average for a region’

Match up Drought Meteorological drought Agricultural droughtHydrological droughtFamine drought Can be accelerated by farming practices such as overgrazing. Rainfall deficiency leads to a deficiency in soil moisture and soil water availability which then has a knock on effect on plant growth and reduces biomass. The result is poor crop yields, and decline in pasture quality. A shortfall or deficiency of water over an extended time period Widespread failure of agricultural systems, food shortages develop into famines that have severe social, economic and environmental impacts. As populations grow and become wealthier, their demand for water also increases. Also natural variability in the climate can cause a temporary decline in supply and stores are not replenished. Shortfalls in precipitation due to short-term variability, or, longer term trends, which increase the duration of the dry period. Lack of rainfall is often combined with high temperatures, high winds, strong sunshine, and low humidity. This increases evaporation. Reduced stream flow and groundwater levels which decrease because of reduced inputs of precipitation and continued high rates of evaporation. It also in reduced storage in any lakes or reservoirs. There are major threats to wetlands and other wildlife habitats. Also linked to decreasing water supplies for urban areas which results in water-use restrictions. http://threeissues.sdsu.edu/three_issues_droughtfacts01.html http://drought.unl.edu/DroughtBasics/TypesofDrought.aspx

Match up Drought Meteorological drought Agricultural drought Hydrological drought Famine drought Can be accelerated by farming practices such as overgrazing. Rainfall deficiency leads to a deficiency in soil moisture and soil water availability which then has a knock on effect on plant growth and reduces biomass. The result is poor crop yields, and decline in pasture quality. A shortfall or deficiency of water over an extended time period Widespread failure of agricultural systems, food shortages develop into famines that have severe social, economic and environmental impacts. As populations grow and become wealthier, their demand for water also increases. Also natural variability in the climate can cause a temporary decline in supply and stores are not replenished. Shortfalls in precipitation due to short-term variability, or, longer term trends, which increase the duration of the dry period. Lack of rainfall is often combined with high temperatures, high winds, strong sunshine, and low humidity. This increases evaporation. Reduced stream flow and groundwater levels which decrease because of reduced inputs of precipitation and continued high rates of evaporation. It also in reduced storage in any lakes or reservoirs. There are major threats to wetlands and other wildlife habitats. Also linked to decreasing water supplies for urban areas which results in water-use restrictions. http://threeissues.sdsu.edu/three_issues_droughtfacts01.html http://drought.unl.edu/DroughtBasics/TypesofDrought.aspx

Types of drought Types of drought and their characteristics Major features Major impacts Meteorological drought Rainfall deficit Low precipitation High temperatures Strong winds Increased solar radiation Reduced snow cover Hydrological drought Stream flow deficit Reduced infiltration Low soil moisture Little percolation and groundwater recharge Agricultural drought Soil moisture deficit Low evapotranspiration Plant water stress Reduced biomass Fall in groundwater levels Famine drought Food deficit Loss of natural vegetation Increased risk of wild fires Wind-blown soil erosion Desertification Drought duration and severity

AFL

Meteorological and Hydrological Droughts Distinguish between meteorological and hydrological droughts (4 marks) Use pages 23 and 24 in Hodder Meteorological is defined by shortfalls in rainfall as a result of SHORT TERM variability Within the LONGER TERM trends overall. This is typical of many semiarid regions = Sahel. There is a rainfall deficiency, high temp and high winds, dry and low humidity, caused by natural variation in the atmosphere. Longer term occurrence linked to climate change or El Nino. Whereas Hydrological is reduced stream flow and groundwater this is due to reduced precipitation and continued high rates of evaporation. Reduced storage in lakes or reservoirs, major threats to wetlands, salinization and poor water quality. Decreased water supplies for urban areas often in developed countries = water restrictions to control abstraction rates e.g 1973 in UK. In Brazil this can be problem where there is no permanent water supply which depend On seasonal rainfall stored in shallow reservoirs . Meteorological drought can give rise to Hydrological and Agricultural droughts!

Agricultural and Famine drought What the main difference between the two?(4 marks) Agricultural drought has reduced plant growth and reduced biomass. There is a soil moisture deficit due to rainfall deficiency and falling groundwater. All leads to poor yields, Decline in pasture quality and livestock well-being. This causes subsistence farmers to need Government aid. Famine drought is the ‘widespread’ failure of agricultural systems, food shortages, severe Social, economic and environmental impacts. Humanitarian crisis levels e.g Horn of Africa in 2012-14 which required ‘international solutions’.

Creeping Hazards? What does this mean? Droughts are known to have a long period of onset of several years which makes it difficult to determine whether a drought has begun or whether its ‘just a dry period’

Intertropical Convergence Zone Intense heating at the Equator by the Sun. Warm air rises here and creates a LOW PRESSURE BELT. Here There is also high evaporation from the ocean. CLOUDS & RAIN 1. 2. The subtropical high is created as the descending arm of the Hadley cells has cold air sinking, this creates HIGH PRESSURE BELTS. HOT DRY CONDITIONS 2. 3. The air returning at ground level is the TRADE WINDS which pick up moisture, They converge at the equator. 3. 4. The warm air from subtropics meet the cold air from the Ferrel Cell. The warm air is forced to rise at the Polar Front. Causing c ondensation and rain called a depression! That’s why we have terrible weather in the UK! 4. Depression move across the Polar front from east to west, directed by the Polar Jet Stream due to the Earths Rotation.

Loops of the jet stream occasionally break up which allows areas of high pressure to form. They can block other weather systems for weeks bringing calm, stable, dry conditions with no rain or wind. Called BLOCKING ANTICYCLONES Met office reported that 2010-2012Much of central and southyern EnglandHad a blocking anticyclone with much reduced rainfall

The movement of the ITCZ The apparent overhead movement of the Sun with the seasons is shown below. For e.g. when the sun is directly over T. Cancer, UK has longer daylight hours 21st 20th 22nd 21st The Hadley cell moves in line with the sun’s m ovement/ Equinox and Solstice. When the Hadley Cell moves 5 degrees north( june ) and south(Dec) of the equator the warm moist air moves with it and the cool dry air moves zones too. This means for the UK, we get the drier, warmer conditions in our summer time. The continent of Africa experiences WET and DRY SEASONS. WET when it arrives due to intense heating and warm air rising = rain. DRY when it moves away as cold air sinks and creates high pressure = hot dry conditions

Meteorological drought Meteorological drought is the cause of some of the worst drought that occurs on this planet. It is caused by a phenomenon that is known as ENSO (El Nino southern Oscillation ) – occurs in the Pacific Ocean BUT has a global impact on weather patterns – intense storms in some places and droughts in others. El Nino events are REVERSALS of normal directions of ocean currents and winds in the Pacific Basin

The El Nino – Southern Oscillation (ENSO) Physical causes of drought only partially understood. Climatic dynamics is the study of interlocked systems of the atmosphere, oceans cryosphere, biomass and land surface, all of which interact to produce the global climate.Studies on drought occurrences indicate sea surface temperatures are an important factor in drought. El Niño – Reverse of Walker cells, high pressure accumulates above Australia = drought. S. America has low pressure = flooding and intense rainfall. The appearance of warm surface water from time to time in the Eastern Equatorial Pacific. La Ni ña – An intensification of the Walker cells. Australia has low pressure, whilst S. America has drought conditions due to high pressure formation. The appearance of colder than average sea surface temperatures in the Central and East Equatorial Pacific. Key term Teleconnections – climatic anomalies which relate to each other at large distance. Teleconnections mean that the development of the ENSO within the Pacific Ocean has an impact on climates around the world. Timescales Occurs every 2 – 7 years although they appear to be getting more regular. Last for approx 1-2 yrs

Normal Year Trade winds move warm surface waters ‘westward’ across the pacific ocean Convectional uplift occurs as the warm air rises and water heats the atmosphere (large cumulonimbus clouds as per image above) this forms rain over Australia Pressure of the trade winds causes sea level to expand due to warmer water near Australia – 8 degrees higher than colder water at Peru.Thermocline is shallow and allows winds to pull up the cold water – this upwelling brings up cold water nutrients and leads to excellent fishing conditions. Warm air rises over Australia and condenses. Air then moves in the Walker Circulation loop eastwards as cold air sinks over Peru causing drier conditions. N

El Nino Trade winds weaken/die, they may even reverse Piled up water in the ‘west’ moves back ‘east’ this then causes rise in sea level by 30cm in Peru - This warm water is 6-8 degrees warmer. This overrides the cold Humboldt Current which breaks the food chain reduces fish numbers and affects fish eating birds in Galapagos Islands Warm rising air with convectional uplift move ‘east = rainfall and floods There is upper jet stream disturbances (Walker Circulation) which affect the whole world - teleconnections N

Meteorological drought Construct new meaning Watch the clip and write notes in the back of your book about how El Nino/La Nina works.

Meteorological drought

La Nina Exaggerated version of a normal year! Strong Walker Circulation loop Extremely strong Trade Winds which push warm water ‘westward’ = sea level rise in Indonesia and Philippines, Australia by 1m Low pressure develops with strong convectional uplift as warm water heats up atmosphere in that area. This causes heavy rains in SE Asia.Increase in the equatorial undercurrent and a very strong upwelling of cold water off Peru results in strong high pressure

What is El Nino, how does it work and how does it cause droughts? Use the Geo Factsheet and the Guardian newspaper article to complete the comprehension grid https://www.theguardian.com/environment/2016/mar/16/drought-high-temperatures-el-nino-36m-people-africa-hunger

What is El Nino? Where does El Nino occur? How often does it occur? How are El Nino events detected? 5. What is the southern Oscillation? Diagram and explanation of how El Nino works Climatic hazards associated with El Nino Case study example: Papua New Guinea Case study example: Southern/Eastern Africa How does El Nino leads to droughts

Homework Use new Geofactsheet and read through the very strong El Nino of 2014/15: Compare the map with this one below.

Extra Reading http:// climate.ncsu.edu/climate/patterns/ENSO.html

Synoptic charts http://www.metlink.org/secondary/a-level/weather-charts/#partc https://www.metoffice.gov.uk/public/weather/surface-pressure/#?tab=surfacePressureColour&fcTime=1471262400http://www.metlink.org/secondary/a-level/weather-charts/ Homework