405, please remember to sign off with your name when you post as well as comment.

Saturday, May 14, 2011


What is hydrograph?

A hydrograph is a graph that reflects the discharge of a river over a period of time. Discharge is the volume of water that flows about a certain point per unit of time.

Discharge: volume of water in the river at a given time.
Construction of storm hydrographs:
  • Rising limb: The rising flood water in the river
  • Peak flow: Maximum discharge in the river
  • Recession limb: Falling flood water in the river
  • Basing lag time: Time difference between the peak of the rain storm and the peak of the river
  • Base flow: Normal discharge of the river
  • Overland flow: Volume of water reaching the river from surface run off
  • Through flow: Volume of water reaching the river through soil and underlying rock layer
  • Storm flow = Overland flow + Through flow
Factors influencing Storm Hydrographs:

1. Size of the drainage basin (Area):
    Larger basin receives more pricipitation -- larger runoff
    Larger basin means water will take longer to reach the river -- longer lag time
2. Shape of the drainage basin:
    Elongated basin -- lower peak flow and longer lag time than circular one
3. Slop:
    Steep slop -- steeper rising limb and shorter lag time
4. Characteristics of the Drainage Basin:
    Permeable rocks and soil mean rapid infiltration and little overland flow -- longer lag time and shallow rising lime
5. Land use and Human impact:
     Afforestation -- intercepts the precipitation -- shallow rising limb and longer lag time
     Urbanization -- tarmac and concrete form impermeable surface -- steep rising limb and short lag time

River management: the presence of a dam will allow flow to be controlled, reducing flood risk and allowing rivers to gradually respond to heavy rainfall in a controlled way. 
A very good website for more information and practice:

Hope you have learnt something. Thank you :)
Xu Ao, JH405, 14

1. http://serc.carleton.edu/introgeo/socratic/examples/hydrosphere.html
2. http://www.bbc.co.uk/scotland/education/int/geog/rivers/hydrographs/index.shtml
2. http://geobytesgcse.blogspot.com/2006/11/hydrographs-and-river-discharge.html

Wednesday, April 27, 2011

How do Clouds Form

While there are a wide variety of cloud shapes and sizes, they are all made of the same thing: condensed water or ice. Clouds form when rising air, through expansion, cools to the point where some of the water vapor molecules "clump together" faster than they are torn apart by their thermal energy. Some of that water vapor condenses to form  cloud droplets or ice crystals which can be observed by us.
formation of a convective cloud

 To be more specific,  in order for these water droplets or ice crystals to form into clouds in the atmosphere, a series of processes have to happen, and different types of clouds form from different processes. The four main ways that clouds can form are:
-Surface Heating
-Mountains and Terrain
-Weather Fronts (cold or warm)
-Air Masses Being Forced to Rise
All of these processes involve the cooling of air. Warm air is able to hold larger amounts of water vapor than cool air, so when air cools it is no longer able to hold all of the water vapor it was able to hold when it was warm. This extra water vapor begins to condense out of the air into liquid water droplets.

there are five main types of clous, which are , cirrostratus clouds, cirrocumulus clouds,altocumulus clouds and cumulus clouds.
cirrus cloudsthere are also four types of cirrus clouds. two kinds of cirrus clouds that we should know is  cirrus Fibratus dsand Spissatus. they are all ice clouds, if you see these to kinds of clouds, it means it is a good wather now. however, the weather also depend on the winds. if the winds are from the E to S, precipitation is likely to occur with 20 to 30 hours of that time period too.


there are 3 types of cirrostratus clouds. these clouds cover up the whole sky. these clouds contain ice. if you see these clouds in the sky, it means that precipitation is likely to occur in 15 to 25 hours.
cirrostratus clouds
cirrocumulus clouds
cirrocumulus clouds are all ince clouds. if you see these clouds in the morning, then that means you will likely to see come thunderstrom showers in the afternoon.
Altocumulus Clouds
Altocumulus clouds are mostly water and ice clouds. one type of altocumulus clouds, undulatus clouds, is the sign for heavy rain.
Cumulus Clouds
Cumulus clouds are the most common clouds. There are 4 types of Cumulus clouds; Humilis, Vertical Growth, one kind of cumulus clouds that we should know is Vertical Growth can also occur during fair weather conditions and can spawn afternoon showers. 
Vertical Growth
Hope everyone can learn from what i post, clouds formation is amazing right ?!!? :D
Zhou Weixin(25)  JH 405

Saturday, April 9, 2011

The hydrologic cycle and different drainage patterns

The hydrologic cycle is the journey water takes as it circulates from the land to the sky and back again. It is a conceptual model that describes the storage and movement of water between the biosphere, atmosphere, lithosphere, and the hydrosphere. Water on our planet can be stored in any one of the following major reservoirs: atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields, and groundwater. Water moves from one reservoir to another by way of processes.

Components (processes and terms) of the hydrologic cycle and their definitions:
  1. Evaporationthe process by which water is converted from its liquid form to its vapor form and thus transferred from land and water masses to the atmosphere. 
  2. Precipitation—water falls back to earth from the atmosphere as rain/snow.
  3. Infiltrationthe process by which water on the ground surface enters the soil.
  4. Condensationthe change of the physical state of water from gaseous phase into liquid phase, 
  5. Surface runoffthe water flow that occurs when soil is infiltrated to full capacity and excess water from rain, or other sources flows over the land. 
  6. Evapotranspiration—movement of water from soil and plants to the atmosphere.
  7. Interception—water is intercepted by plants and trees.
  8. Through flow—water that flows horizontally in the soil zone.
  9. Water vapour—gaseous phase of water
  10. The Earth's Water Budget – the distribution of water among the oceans, land and atmosphere.
Putting everything together:
The total quantity of water on the earth remains essentially constant. Water moves about from high ground to low ground, changing location and form (vapor, liquid, solid) as part of the hydrologic cycle. Water vapour in the atmosphere condenses due to the cooler temperature to form clouds (condensation).  Water is delivered to the earth as precipitation (rain or snow) and then seeps into the ground (infiltration) or travels over the ground (surface runoff). Some of the water moving over land or in streams and lakes is lost to the atmosphere as water vapour through evaporation. In addition, plants extract water from the ground and release it to the atmosphere as water vapor (transpiration). Water loss to evaporation and transpiration are referred to collectively as evapotranspiration. Water that has seeped into the soil moves along as through flow and water which runs off to streams moves as stream flow. J

A simple diagram to illustrate the hydrological cycle:

Further Learning on Hydrologic Cycle:

Figure 2: Hydrologic Cycle

A good website for further reading on hydrologic cycle:

Different Drainage patterns

 Dendritic drainage pattern

Trellis drainage patterns

 Radial drainage pattern

Other drainage patterns include: rectangular drainage pattern, parallel drainage pattern, centripetal drainage pattern, deranged/contorted patterns.

A very good website for more information: http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/fluvial_systems/drainage_patterns.html

Thank you. :) Hope you have learnt something.
Yang Yi Chao  JH405  15 :)



Wednesday, April 6, 2011

Types of rainfall

Hi everyone! I'll be sharing with everyone about the different types of rainfall today. Some might wonder, rain is simply water droplets falling back onto earth, how different could it possibly get?! But yes, there're in fact 3 different types of rainfall, and I'll be explaining them to you in detail.

1. Convectional rainfall

This is the type of rainfall we get in Singapore :) As the name suggests, it is a result of convection of the wind patterns on earth. Warm air rises and cold air sinks in the convectional current due to density. The hot air and the rays from the Sun intensely heat the ground, and the warm ground warms the air immediately above it. This produces a bubble of warm air that begins to rise. This air cools as it rises in the atmosphere and eventually reaches a dew point temperature causing clouds to form. As these clouds accumulate, the water vapour that has condensed to form water droplets inside will be too heavy, and fall back to earth as rain. This rain is usually heavy and lasts for only a short period of time.

Here's a simple illustration to aid everyone:

2. Orographic rainfall

You can find this type of rainfall at some of the earth's great deserts :) The word "orographic" means that it is related to mountains. When moist, warm air from the sea evaporates, the air is forced up against mountain slopes at places with mountains. At the tip of the mountain top, air formed is cooled at dew point, before condensing to form water droplets, which ultimately fall back down as rainfall. At mountainous regions, air drops down over the high ground, gaining temperature and increasing the amount of water it can hold. That is why the flat regions below mountains hardly experience rain, and this area is known as rain shadow. This is a diagram to illustrate orographic rainfall:

3. Frontal rainfall

Frontal rainfall is caused when frontal systems form when warm and often tropical air meets cooler air. Stratiform precipitation falls out of nimbostratus clouds. Nimbostratus clouds are a formless cloud layer that is almost uniformly dark grey. Usually, nimbostratus is a sign of steady moderate to heavy precipitation. It looks something like this:

Scary, isn't it?! ):
Back to the point on warm and cool air. As hot air is lighter and less dense than cold air, it rises over it. As warm air is forced to rise further, condensation occurs at dew point, and over time rain droplets will accumulate, resulting in the scary looking cloud as seen above (because the water droplets block out sunlight from the Sun).

On the other hand, when heavier and denser cold air pushes beneath and lifts the warm air, a cold front occurs. This causes lowered pressure along the cold front and can cause the formation of showers and thunderstorms when enough moisture is present.

Alright, I hope that everyone has learnt a new thing or two through this new entry. Tata for now :)

Done by: Clarissa (7)

Friday, March 18, 2011

Global Wind Patterns

Hello everyone, this post is about global wind patterns. Hopefully it may help us understand this topic better! :)


A big layer of air called the atmosphere surrounds the Earth. The air within this layer moves from place to place when it warms up or cools down. This moving air is known as wind
All of these winds are part of a global air circulation system that acts to balance temperature and pressure around the world. In addition, winds move moisture and heat around the world and also produce much of our weather.


Energy from the Sun heats the entire Earth, but this heat is unevenly distributed across the Earth's surface. Equatorial and tropical regions receive far more solar energy than the mid-latitudes and the Polar Regions.
The tropics receive more heat radiation than they emit, while the Polar Regions emit more heat radiation than they receive. In the other words, there is a net loss of solar radiation in the higher latitudes and a net gain in the tropics. If no heat was transferred from the tropics to the polar regions, the tropics would get hotter and hotter while the poles would get colder and colder. This latitudinal heat imbalance drives the circulation of the atmosphere and oceans.  (Around 60% of the heat energy is redistributed around the planet by the atmospheric circulation and around 40% is redistributed by the ocean currents.)
As equatorial areas are heated most, the air above them warms and rises as it becomes lighter than the surrounding air, causing an area of low pressure. In cooler areas, the air sinks because it is heavier and results in an area of high pressure. Winds will blow as air is squashed out by the sinking cold air and drawn in under the rising warm air. Any difference in temperature like this will always cause a difference in air pressure – and therefore winds will blow. A good expression to remember is that:

"Winds blow from high to low" (i.e.: from high pressure to low pressure).

 Atmospheric Circulations

The following three diagrams describe the basic atmospheric circulation system.

Figure 1: Cross-section of the atmosphere with uniform horizontal atmospheric pressure.

In this first diagram (Figure 1), there is no horizontal temperature or pressure gradient and therefore no wind.

Figure 2: Development of air flow in the upper atmosphere because of surface heating.

In the second diagram (Figure 2), the potential for solar heating is added which creates contrasting surface areas of temperature and atmospheric pressure. The area to the right receives more solar radiation and the air begins to warm from heat energy transferred from the ground through conduction and convection. The vertical distance between the isobars becomes greater as the air rises. To the far left, less radiation is received because of the presence of cloud, and this area becomes relatively cooler than the area to the right. In the upper atmosphere, a pressure gradient begins to form because of the rising air and upward spreading of the isobars. The air then begins to flow in the upper atmosphere from high pressure to low pressure.

 Figure 3: Development of a closed atmospheric circulation cell because of surface heating.

Figure 3 shows the full circulation system in action. Beneath the upper atmosphere high is a thermal low pressure centre created from the heating of the ground surface. Below the upper atmosphere low is a thermal high created by the relatively cooler air temperatures and the descend air from above. Surface air temperatures are cooler here because of the obstruction of short wave radiation absorption at the Earth's surface by the cloud. At the surface, the wind blows from the high to the low pressure. Once at the low, the wind rises up to the upper air high pressure system because of thermal buoyancy and outflow in the upper atmosphere. From the upper high, the air then travels to the upper air low, and then back down to the surface high to complete the circulation cell.

Single-Circulation Cell

One way to transfer heat from the equator to the poles would be to have a single circulation cell where air moved from the tropics to the poles and back.  This  model was first proposed by Hadley in the 1700’s.   Figure 4: Single-cell circulation

Wind Cells

Since the Earth rotates, its axis is tilted and there is more land in the Northern Hemisphere than in the Southern Hemisphere, the actual global air circulation pattern is much more complicated. Instead of a single-cell circulation, the global model consists of three circulation cells in each hemisphere. These three cells are known as the Hadley cell, the Ferrell Cell and the polar cell.

                                                               Figure 5: Wind cells

1. Hadley cell - This is the cell that is closest to the equator.  It consists of winds converging and rising at the equator and then diverging north and south of the equator as it reaches the upper troposphere.  The winds then sink at 30 degrees latitude as they converge with winds in the Ferrell Cell.  They hit the surface and diverge back to the equator to complete the cell. 

2. Ferrel cell - This cell has winds sinking at 30 degrees latitude and then travelling pole-ward as they hit the ground and diverge with winds from the Hadley Cell.  These winds travel towards the poles until they converge with winds in the polar cell at 60 degrees latitude.  These winds then rise up and spread out equator-ward to complete the cell.

3. Polar cell - This cell has winds rising up at 60 degrees latitude and spreading out pole-ward as they reach the upper troposphere.  The winds sink down at the poles and then diverge towards the equator until they reach 60 degrees latitude where they rise up again to complete the cell.

                                                         Figure 6: global wind patterns
Although still oversimplified, this three cell model can describe the main features of atmospheric circulation.


Done by: Zhexian

Sunday, March 13, 2011

The Ozone Layer

I'll be posting about the Ozone Layer because I think a lot of people have slight misunderstandings of the Ozone Layer with regards to the greenhouse effect. 

To recap, the ozone layer is in the stratosphere. 
image taken from: http://www.cec.org/ods/en/module01/cec_odspolicy_m01t01p01_e.asp?print=1
The ozone layer is made up of ozone molecules, O3. The ozone layer is extremely important to us because it absorbs the very harmful UV rays from the sun, preventing them from coming down to Earth's surface, thereby protecting us. These harmful rays can cause skin cancer and many other forms of genetic problems in living organisms. 
Ozone is a greenhouse gas. Greenhouse gases absorbs heat reflected back by Earth's surface. The ozone layer absorbs heat as well. In the recent years, the increased use of chlorofluorocarbons, CFCs, has led to an increased depletion of the ozone layer. CFCs are broken into free radicals by UVt light in the stratosphere. These free radicals then break down more than ten thousand ozone molecules. Thus there are holes in the ozone layer. 
These holes allow more harmful UV rays to reach Earth's surface, dramatically increasing skin cancer/disease rates, especially in Australia which is near the hole above Antarctica. 
Although there are more UV rays entering, it does not affect the heat budget. This is because UV rays aren't considered "heat". The heat budget is dependent on the insolation (incoming solar radiation), in other words, infrared radiation, which doesn't require a medium to travel. So, with or without the hole in the ozone layer, the heat absorbed by Earth from the Sun remains the same. 

Greenhouse gases include Methane, Nitrous Oxide, Water vapor, Carbon Dioxide and Ozone. 
image taken from: http://eo.ucar.edu/kids/green/warming4.htm
The greenhouse effect refers to the greenhouse gases absorbing heat and warming up Earth, sustaining the temperature at which we can all survive in. Without the greenhouse effect, Earth would be too cold to live in. You may have heard of people saying that greenhouse effect is a bad thing, but it is not. It is just that people are concerned about the increasing amount of Carbon Dioxide, which leads to global warming. 
Global warming is the increase of Earth's temperature, mainly due to the increase in the amount of carbon dioxide. With more greenhouse gases, more incoming radiation from the Sun would be absorbed, warming Earth up even more. Thus affecting the heat budget. 
Please correct me if i made a mistake, coz i wrote these from what i understand.

Sunday, February 27, 2011

Breaking news

Hey people,
I will be covering the World News worksheet based on the articles on drought in France and Australia.
What is the climate? Where is the country located? What is happening?
France is located in Europe, with a temperate climate, and a rather moderate amount of rainfall is facing water shortages due to drought and dry weather.
Australia has an arid climate, low rainfall and high temperature is facing heavy downpours. Queensland is hit by cyclone, Perth, which was threatened with cyclone, is suffering from bushfires and Sydney is suffering from heat waves.

Why? How?
France is facing the worst water shortage since 1976, due to drought and dry weather. Reservoirs and rivers are drying up so fishes and crops are dying. Fines and patrols of “water police” were put in place to enforce restrictions on irrigation and ensure that people do not waste water. Resulting in many people loses money from their farms and more people become unemployed. This could have been a result of higher amount of carbon dioxide, which causes more heat to be trapped in our atmosphere, so lakes start to evaporate and drought occurs.
Australia is facing heavy downpours. One of the biggest cyclones hit Queensland, Perth threatened with a cyclone last week is currently suffering from bush fires, while Sydney is suffering from heat waves. This could be due to the increase in evaporation from lakes due to increase heat trapped in the atmosphere, so the amount of water vapor in the atmosphere increases, causing heavy downpours.

The above would lead to the people being injured and even death. Buildings are damaged, livestock are killed and people would become homeless and suffer from hunger. The food industry will be affected, since the supply of food decreases while the demand of the people increases. If the problem persists, food prices will rise. Bushfires would damage more plants and increase the amount of carbon dioxide in the atmosphere through the burning of plants. Also, there are lesser plants to recycle carbon dioxide for oxygen. So the heat budget becomes even more imbalance as more carbon dioxide traps heat in the atmosphere. Leading to long-term effects such as temperatures rising, glaciers melting and rising of water level. 

Picture of Carbon cycle and heat budget

Done by: Lydia :)