Lesson 5. The causes of droughtWhat is drought?

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Match up task

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.

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A shortfall or deficiency of water over an extended time period

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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.

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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.

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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.

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*****Please add the red arrow along the right hand side of the table – as per the PPT

Add the following major impacts into the correct type of drought: (some boxes have less impacts than others, there’s not an even spread)

Poor yields Widespread failure of agricultural systems Loss of soil moisture Irrigation systems start to fail International aid required Supply of irrigation water declines Threats to wetlands and wildlife habitats Rural industries affected Rural-urban migration Reduced storage in lakes and reservoirs Pasture and livestock productivity declines Humanitarian crisis Poorer water quality Rural economy collapses Less water for urban supply and power generation – restrictions Food shortages on a seasonal scale Some government aid required Increased malnutrition and related mortality

Distinguish between meteorological and hydrological droughts (4 marks) Use pages 23 and 24 in Hodder

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Outline the main difference between agricultural and famine droughts (4 marks) Use page 24 Hodder_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Why are droughts described as ‘creeping hazards’?_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

El Nino Southern Oscillation (ENSO)

Looking the map, where does El Nino occur?

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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.

EL Nino Year

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

La Nina Year - Exaggerated version of a normal year!

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

Homework Research

Use the internet to research the very strong El Nino of 2014/15: there are numerous newspaper and scientific sources make a map of possible climate extremes similar to the one below and compare the two. See image over the next page.