Hydrological cycle

31th, March, 2009

Hi, class!
Today we learned a lot!
Basically, we can divide the content we learned today into five part

1) the teacher recap on what we learned during the last lesson -infiltration
Let's see the diagram above.

In this diagram, infiltration, overland flow and water table are labeled.

When the soil is saturated, there is overland flow instead of infiltration.

2) Input & output storages & Flows

what is input in hydrological cycle? It is Precipitation! (note: not rain, must be precise!)

Basically, Output inclueds evapotranspiration and Riverflow.

For Storages, there are 2 types of storages. Below water table, there is ground water storage, above water table, there is soil moisture storage.

For Flows, there are channel flow (river), Percolation, Throughflow and Baseflow.

Ms Tang told us, Channel flow is usually river, Percolation occurs after infiltration, when water still flow downwards in soil. Percolation can result in Groundwater storage. As for Throughflow, it is the movement of Soil moisture storage. And baseflow is the movement of the Groundwater storage.

Accoding to the order (from the surface of the ground to the deep underground), there are
-Channel flow

-Percolation

-Throughflow

-Baseflow

For Baseflow, as we can see from the diagram above, it occurs below the water table. Furthermore, it can recharge the river as where water table emerges at ground surface, it forms river/lake.

3) Roles of vegetation in the "interception" component of the hydrological cycle.

Firstly, the roots plays an important role to encourage water to pass into the soil and rock.

Secondly, vegetation slows down the water flow by reducing rainsplash erosion. So what is rainsplash erosion? In my opinion, it is like that each drop of water drips on the ground and it "hit" the ground, gradually, the soil there will be more compacted. In this way, it will decrease the rate of infiltration as it becomes harder for water to go through the soil. However, when there is vegetation, each drop of water splashes, thus, there will be a less great impact on compaction of soil. Hence, the rainsplash erosion is reduced.

Thirdly, the leaves collect water and the water is then evaporated or there will be throughfall (water drips from leaf) and stemflow ( water flows along the stem).

Also, vegetation itself needs water to sustain its life, some amount of water will be stored inside the plant organs to supply water when the plant is "thirsty" and there is no water it can absorb from the outside world.

In conclusion, vegetation really plays a very important role in the hydrological cycle. For the 2 countries which locate next to each other and share very similar geological features may still have big differences in their rainfall and climate. Presence of vegetation is also a factor which affects the local weather and climate. Or we can see it in another way. Presence of vegetation is a good indicator for the local general climate. In a dessert, it is very dry, there is little vegetation. However, in a tropical place, where there is always humid, we can see much more vegetation.

4) water balance
we need to know that there is usually a water balance in nature:

(I think this is due to the regulatory force in system, it is a negative feedback)
input=output
there is one equatin
Precipitation=Evaportranspiration+Qrunoff+change in soil moisture Storage

P=E+Q+change in S (this equation is a little bit different fromt the equation in notes, but i think this one is easier to understand and remmember!:)
there is one more thing, if we want to keep the soil moisture storage constant, what can we do? -To make the soil saturated. Thus, no more water can be stored in soil. In this way, it will result in overland flow.

5) Storm Hydrographs
this is the last part which Ms Tang went through roughly. For more details, please refer to Page 22 in your notes.
The hydrograph is a graph that shows change in discharge of a river. Discharge refers to how much water is flowing through a particular point per second (unit: m3/s)
It is a good way to record precipitation and it is useful when there is flood.

Guys, I know there is a lot which we need remmember, just try to understand it first, then I think it will be much easier to remember the tedious"scientific terminologies". Actually, I realised each terminology has its own reasonable meaning behind the word/phrase, just understand it frist. (For e.g. stemflow, water flows along the stem.) I think we can try some research on some certain case studies to know the process of hydrological cycle and the importance of water balance better.

Water is a precious resource. As we are learning geography hydrology now, let's treat water as a friend, let's have a try to know her better!

-Chengxi:D

▁▂▃▄▅▆▇ Infiltration ▇▆▅▄▃▂▁

Haha~hello,05!! ❤

This is our first half-hour period of geo lessons. Last lesson we discussed about how water is important and essential in our life and the drainage basins. And this lesson was started with an experiment. Our class was divided into 5 groups and each group got a cup of soil and an empty cup with a drawn line on it. We poured the water into the empty cup until it reached the drawn line every time and poured the water into the cup of soil slowly, observed how water flowed inside the soil carefully. We were supposed to see the water flowed slower and slower until a layer of water was formed on the surface of soil. But in our class, all groups except our group said they saw the water flowed faster and faster. Miss Tang said it might due to some other reasons like the speed we poured the water into the soil. ☻

From this experiment we did, we could guess what will affect the rate at which water soaks into the soil which is called the infiltration capacity or infiltration rate. We deduced some factors of it, for instance, the presence of rock, the amount of water in soil, how compact the soil is, the permeability of soil and the presence of vegetation (the roots will increase the rate of infiltration). And sometimes if the amount of water received by soil exceeds the infiltration capacity of soil, it will lead a collection of water on the surface which is also can be called overland flow. Because of the limit of time, we did not learn it very concretely and I think Miss Tang will teach us more specifically to let us understand it better during next lesson. ☺

Yay, I think that’s all we have learnt in this lesson.

JIA YOU PEOPLE!!! :) :) :) :) :) :) :) :) :) :) :)

-Liu Fan- ❤

WATER!(:

24th March.

We had a rather exciting lesson, with the bee and all.

We were asked to write down what came to our mind when we thought about water. And we came up with things like AQUA, rain, rivers, ice and even things like pee, just to name a few. I guess this was to have an idea of what we think water is all about right at this moment before we learn anything more about it. (I don't have a picture of the stuff we wrote on the board!)

We were given a reading which was (to me) a rather big mix of chemistry, physics and even a bit of biology. It is rather cool to understand that water when frozen has a lower density as compared to water (in liquid form) so it floats and so it freezes only the top layer! By only freezing on the top layer, our dear water creatures can still live because the rest of the water isn't frozen.  Other than that, we also learnt that water is a versatile a unique molecule that is compatible for life. Water has a range 100 degrees Celsius in liquid form. And as Ms Tang said, since we are made up of 70-80% water, imagine if the range of water in liquid form is like most liquids at a range of about 20 Degree Celsius, standing out in the sun could just cause us to evaporate or experiencing winter could cause us all to freeze and become ice blocks. I really am starting to appreciate water now. [Of course, this is another reason why we should all save water.]

The specific heat of water, which is the amount of energy required to raise the temperature of a substance in this case water, is particularly high as compared to other liquids for life. It is harder to raise the temperature of water. And as we know, large portions of the Earth is covered with water and not forgetting that the changes in temperature of water bodies could result in widespread flooding, melting of glaciers. Thus, the specific heat of water helps to maintain Earth's fairly stable climate.

Another interesting fact is that water is a universal solvent! Many substances can dissolve in water.

Now we know why water is so essential for life!(:

Then we went to somewhere behind the classroom block to talk about drainage basins. In my understanding, a drainage basin is an area where water drains downhill into a body of water. So there has to be

1. water

2. relief (so the water can flow downwards)

3. land (can be soil, concrete, anything. It does not have to be of common material)

The water can fall in any part enclosed within the dotted lines and it will flow to the bottom. The brown dotted line is an imaginary line that roughly marks out each drainage basin. This imaginary line is called the water shed.

That's all for the lesson!

Shanice

Global Air Circulation!

Miss Tang taught us more on Global Air Circulation for today's lesson. :)

In the previous lesson, we covered the distribution of the earth's climate. After learning more about the distribution of the earth's climate, some of you might have been wondering why desserts are not found at the equator since that is where the earth receives the greatest amount of solar isolation per year.

The answer to why desserts are not found at the equator is actually because of the way air moves around earth.

Miss Tang first explained how the one cell model accounted for why desserts are not found at the equator. The one cell model is based on three assumptions.

1. The Earth does not rotate.
2. The Earth is made of similar materials.
3. Wind blows form a higher pressure to low pressure.

Based on these assumptions, air circulation on the Earth should approximate the patterns on the above one cell model.

Air flows from the poles to the equator. When the air reaches the equator, it is lifted vertically by the processes of convection and convergence. Air then flows horizontally from the equator to the poles. At the poles, the air in the upper atmosphere then descends to the Earth's surface to complete the cycle of flow.

However, the one cell model does not take into consideration planetary rotation. Planetary rotation would cause the development of three circulation cells in each hemisphere rather than one and these three circulation cells are known as the: Hadley cell; Ferrel cell; and Polar cell.

Both the polar cell and the Hadley cell are driven by heat. However the Ferrel cell is induced. Unlike the other two cells, where the upper and low-level flows are reversed, a generally westerly flow dominates the Ferrel cell at the surface and aloft. The stronger downward vertical motion and surface convergence at 30°N coupled with surface convergence and net upward vertical motion at 60°N induces the circulation of the Ferrel cell.

This three cell model can explain why desserts are not at the equator. From the pervious lesson on rain formation, we know that there must be adiabatic cooling for rain to form. Air must rise, cool and condense to form clouds. However, as observed from the diagram above, there is only sinking air at 30◦ N. Hence, clouds cannot form and thus there is no rain.

The lack of rain at 30◦ N explains why desserts are found there instead of the equator which is where the earth receives the greatest amount of solar isolation per year. :)

Lastly, remember

Good Attitude
Engagement
Ownership
Growth

Is important during Geog lessons :)

Love,
Jeanette.

WHY ARE THERE SEASONS?

HELLO PEOPLE!

Spring,
Summer,
Autumn,
Winter!

Which is your favorite season?

In today’s lesson, we discussed on the topic “Why are there seasons?”. We read through the notes Miss Lin gave to us and tried to understand it by discussion it in our little groups. The groups than sent a representative to share on what they have discussed on. However, during the first round of sharing, the explanations were rather superficial they touch briefly on the tilt of axis and the revolution of Earth around the sun. However, the explanations had no direct link to why seasons existed.

In my opinion, I feel that the main reason why such superficial answers were given was due to the fact that we were unable to visualize this system actually works. We managed to do a better job when Miss Lin gave us a second chance to relook into our explanations.

First we must know that the Earth spins on a tilted axis (23.5˚ from the plane of orbit of the Earth) about once every 24 hours. Without this tilt, no matter how the Earth revolves around the sun, there will be no seasons as every point of the earth will not experience any change of intensity of sunlight. All seasonal changes are driven by changes in the amount of the Sun's energy. This is one of the most important reasons for seasons.

In addition to the earth rotating around its axis, the Earth completes one revolution around the sun about once every 364 1/4 days. The diagram above illustrates the various positions of the earth around the sun. The darker part of the globe represents the part of the earth that does not receive sunlight while the brighter part of the globe represents the part of the earth that receives sunlight at that period of time. The red line on the globe represents the equator. This equator will divide the earth into halves, North and South Hemispheres.

Why is the equator the hottest?
Although every part of Earth which is facing the sun receives the same amount of light rays, the rays at the poles are spread out over a larger surface area compared to equators. Therefore, the intensity of light rays is greater at the equator. Refer to Figure 1.

Figure 1.



At 1, December 21-22, the southern hemisphere experience the longest day as it has the maximum tilt towards the sun. This means that it will receive a great amount of insolation and it will be warmer. On the other hand, the northern hemisphere experience the shortest day as it has the maximum tilt away from the sun. This means that it will receive a small amount Hence the North Hemisphere will experience winter while the South Hemisphere will experience summer.

At 2, March 21-22, the hours of day and night gradually become the same. Therefore, this means that the temperature is generally the same in the two hemispheres. Due to the fact the number of hours spent during the day in the South Hemisphere is shorter compared to that of the season prior to it, the temperature will drop. On the other hand, the North hemisphere generally becomes warmer. Hence, the North hemisphere will experience spring while the South hemisphere will experience autumn.

Okay, so here’s the main gist of the lesson. : )
Jia you for assessment week! XD
<3 Melissa-Raye Teo