Key Idea 1: Weather and Climate

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1 Key Idea 1: Weather and Climate 1.1 What physical factors lead to variations in climate in different regions of the world Weather Climate The day to day changes in the atmosphere. It is constantly changing. The overall pattern of weather, usually based on an average over 30 years. Weather includes: sunshine hours, wind speed / direction, precipitation, temperature etc Measures average temperature and average precipitation each month What affects weather and climate around the world? Latitude This is distance north or south of the equator. As the Earth is curved it affects how much surface area the sun has to heat this makes it cooler further from the equator. It has more land to heat closer to the poles so the amount of heat will be less at these points. Altitude This is the height of land above sea level. Temperatures are colder the higher up you go. They decrease by 1 c for every 100m in height. As air rises it cools; the higher you are the more it has cooled. As altitude increases the temperature will therefore decrease, giving different climatic and weather conditions. Oceans The distance from the sea and the temperature of the sea closest to land. The seas warm up more slowly and cool down more quickly and this moderates the climate of the land next to it. Oceans currents are warm or cold and these change the temperature of the prevailing wind, affecting the climate. Ocean Currents Explained Wind blows over the ocean and the temperature is alerted. If there is a warm current the wind will be warmer and therefore make temperatures on land warmer. This is why Britain has a milder climate than expected for its latitude as the Gulf Stream flows up past the west coast, warming the country Distance From Oceans Explained Oceans heat up and cool down much more slowly than land. This means that coastal locations tend to be cooler in summer and warmer in winter than places inland at the same latitude and altitude. Glasgow, for example, is at a similar latitude to Moscow, but is much milder in winter because it is nearer to the coast than Moscow.

2 Key Skill: Describing a Climate Graph: A climate graph gives you the average monthly rainfall and average monthly temperature for a particular location. The bars show you rainfall (precipitation) and the line shows you temperature. Describing the pattern means saying what is happening over the course of the year for both temperature and rainfall. You must use data from the graph for full marks. Eg The rainfall in this location varies through the year. It is wettest between October and May and drier between June and September. The wettest month is December when 70mm of rain falls and the driest month is June when 7mm of rain falls. Temperature also varies and is highest between May and September, when it is also driest. The coldest months are between November and May. The hottest months are July and August when it is 29 c and the coldest month is January which is 9 c. This gives temperature range of 20 c over the year. Characteristics of Different Climates: Mediterranean Climate: Location: - Found between the 30o and 45 degree latitudes. - Often found on the western sides of continents. - Gets its name from the climate found around the Mediterranean Sea. General Features: Temperature / Precipitation: Plants and Animals Found: - Very mild (few extreme temperatures) - 2 seasons: summer and winter. Summers are longer than winter, and the winter is very mild. - Few places experience snow in a Mediterranean climate. - The seasonal changes are due to changes in ocean currents and water temperature. - Warm to hot, dry summers and mild to cool, wet winters. - Cause of this climate is directly related to large bodies of water such as the Mediterranean Sea and ocean currents. - During the summer, cold currents keep the climate mild and dry. - Ocean currents shift as the seasons change. During the winter the water that was warmed up all summer moves in and keeps the land warm and often brings rain. - Plants must be able to survive long dry summers. - Evergreens such as Pine and Cypress trees are mixed with deciduous trees such as some Oaks. - Fruit trees and vines such as grapes, figs, olives, and citrus fruits grow well here. - Other plants include what are called "scrub", which include small shrubs, grasses, and herbs. - Animals must be able to live in rugged land and not depend too much on large areas of grass to graze. - Natural wildlife found here include goats and sheep.

3 Impact of the Mediterranean Climate on People s Lives: There is often a drought in summer - So farmers must conserve water and grow crops that can survive without large amounts of irrigation. - There may be shortages of water and people may not be able to water gardens / fill swimming pools The sun can be very strong during the summer There can be heavy thunderstorms and rain storms - Care must be taken when out in the sun as skin cancer / sunburn could be an issue - It is often too hot in the middle of the day to be outside so the working day may need to be adjusted to allow for this - This can cause flash floods and endanger lives as the ground will be baked hard by the sun and mean there is little infiltration - Flash floods are hard to predict and prepare for meaning the damage / impact is greater Tropical Climate: Location: - Found along the equator, usually within 25 degrees of the equator - Large areas of Tropical Wet are found in Brazil, Democratic Republic of the Congo, Indonesia, and the Philippines. General Features: Temperature / Precipitation: Plants and Animals Found: - Seasons don't change in a tropical climate it is hot and wet all year round - The region always gets direct sunlight / warmth - Temperatures stay the same throughout most of the year, average of 27 c - Temperatures feel hotter because the humidity is usually very high (amount of water in the air). - Tropical climates are very wet all year round - There is heavy rainfall every day 9usually in the afternoon) - The regular rainfall is caused by the regular warm temperatures - Tropical climates receive over 750mm of rain a year - The constant rain and direct sunlight at the equator allow tropical rainforests to develop. - Since the main vegetation is forests, monkeys are common as well as snakes, frogs, birds, and small mammals - The largest group of animals are insects. Impact of the Tropical Climate on People s Lives: There is a large presence of many tropical diseases eg malaria which have no vaccination Poor soils and climatic conditions make large scale crop growing difficult - So people need to avoid being bitten and often fall ill / die as a result (higher death rates, lower QoL) - costs to the country s economy - Farming needs to be carefully managed so as not to ruin soils and make it so nothing can grow - Can be food shortages if large populations living in an area

4 The length of day and night is equal - Less time to complete chores / work makes it harder especially as much of the climate is found in LEDCs where there may be a lack of electricity and therefore light 1.2 Why does it rain? warm air causes water in the sea and lakes to evaporate warm air and water are forced to rise rising air cools air is cooled to dew point further cooling gives condensation further cooling causes precipitation In simple terms, rain happens because air rises and cools. As it cools it can hold less moisture (air has moisture in it because of evaporation from water bodies like lakes, rivers, seas) and vegetation (transpiration) and so the moisture condenses and forms clouds which if they grow heavy enough will lead to rain (precipitation) as the cloud can no longer hold all the moisture. What causes air to rise / cool (and therefore leads to cooling and rainfall)? Relief Rainfall: Relief rainfall happens over hills. Air is forced to rise over hills / mountains and therefore cools. It brings rain at the top of the hills and as the air sinks again on the other side, it warms meaning it can hold more water and so there is no rain. This area is called the rain shadow.

5 Frontal Rainfall: This rain happens when warm and cold air meets. Cold air sinks under the warm air mass forcing the warm air upwards which cools it. This causes condensation, clouds and rainfall. Convectional rainfall (caused by intense heat so common in the tropics): Convectional rainfall is caused by the sun heating the ground. The heated ground will warm the air above it which makes it lighter and therefore causes it to rise, evaporating surface water with it. As the air rises it cools and condenses and often gives short and intense rainfall. It usually occurs near the equator where the sun is most intense. 1.3 What are the causes of weather hazards associated with both high and low atmospheric pressure? 1.4 How do extreme weather hazards affect different groups of people? Air Pressure = How much the air is pushing down on us. It has a big influence on the weather that is experienced globally.

6 Air pressure globally varies depending on whether it has high or low amounts of solar energy. The UK has changeable weather as it sits in an area where high and low pressure meets. High and low pressure areas bring different weather at different times of the year. Low Pressure: Low pressure means the air is rising which causes it to cool. This forms clouds and leads to rain. The lower the pressure the worse the weather will be. Depressions develop when warm air meets cold air. This is called a front and will usually bring cloud and rain. Depressions are areas of low atmospheric pressure which produce cloudy, rainy and windy weather. These low pressure systems often begin in the Atlantic, moving eastwards towards the UK. They are responsible for the very changeable weather which is common across the British Isles. The diagram shows a depression with a leading warm front and a trailing cold front moving from West to East across Britain. At the warm front, lighter, warmer air from the south (tropical maritime air) meets cooler air from the north (polar maritime air) and rises gradually over it... As the warm air slowly rises it cools, its water content condenses, and clouds form (nimbostratus then altostratus). The result is steady rain, later giving way to drizzle, and finally clearer skies with high cirrus clouds. Behind the warm front is an area of warm, rising air and low pressure - the centre of the low pressure system. As this part of the depression passes over, there may be a short period of clear, dry weather. But not for long... At the trailing cold front, heavier, cooler air meets the warm air at the centre of the depression, undercutting it and forcing it steeply upwards. Quickly moving air masses produce high winds and cooler temperatures... As the rapidly rising warm air cools, its water condenses, and clouds form (cumulonimbus, then cumulus). The result is heavy rain or thunderstorms, giving way to showers, and finally to clear skies as the cold front moves away eastwards.

7 Low Pressure Weather Hazards: Hurricanes / Tropical Cyclones: A hurricane is a large rotating storm with high speed winds that forms over warm waters in tropical areas. Hurricanes have sustained winds of at least 74 miles per hour and an area of low air pressure in the centre called the eye. Formation: Hurricanes form over the warm ocean water of the tropics. When warm moist air over the water rises, it is replaced by cooler air. The cooler air will then warm and start to rise. This cycle causes huge storm clouds to form. These storm clouds will begin to rotate with the spin of the Earth forming an organized system. If there is enough warm water, the cycle will continue and the storm clouds and wind speeds will grow causing a hurricane to form. Location: Hurricanes / tropical cyclones occur over the ocean in areas near the equator. This is because there is plenty of warm water in these areas to allow the storms to form. There are seven major areas in the world that tend to produce tropical cyclones. See the map below. Effects / Response / Impact on Different People: SEE CASE STUDY: CYCLONE NARGIS

8 High Pressure (Anti-cyclones): Anticyclones are areas of high pressure which form where cool air sinks. They usually cover large areas and give long periods of settled weather. Weather Conditions: - As the air is sinking, not rising, no clouds or rain are formed. This is because as the air sinks it warms, meaning it can hold more water. - The absence of fronts means winds may be very light. - Consequently, high-pressure areas are often associated with settled, dry and bright conditions. - In summer, anticyclones bring dry, hot weather. In winter, clear skies may bring cold nights and frost. - In cold conditions, anticyclones may also bring fog and mist. This is because the cold forces moisture in the air to condense at low altitudes. British Summer anti-cyclone - Can cause heat waves during the day - At night as there are no clouds, heat will be quickly lost so it gets much cooler - The ground will cool sufficiently to cause condensation of water vapour in the descending warm air and mist or heavy dew may form in the morning - After a few days, a layer of hot air builds up at ground level, which eventually will give rise to thunderstorms, ending the anticyclone. - Summer anticyclones can result in Heat wave conditions with temperatures significantly above average. British Winter anti-cyclone - The longer nights combined with clear skies leads to intense cooling of the land. - There is an increased risk of dew, frost and thicker, more extensive fog patches which may be slow to clear or even persist. - Under very calm conditions, both frost and fog may persist for several days. - An anticyclone's very stable conditions and little air movement means that pollution is trapped at low levels, resulting in very poor air quality such as smogs. Anti-cyclones in summer can lead to extended periods with no rainfall and consequently cause drought conditions which are hazardous to different groups of people in many parts of the world. Effects / Response / Impact on Different People: SEE CASE STUDY: BARCELONA DROUGHT