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Unlock This CourseA climate graph shows the temperature and rainfall of one place for each month of the year. It is really two graphs in one: a line for temperature and bars for rainfall. The months go along the bottom. One side has a scale for temperature in °C and the other side has a scale for rainfall in mm.
Key terms:
Here is the data for Town P, a made-up place.
| Month | J | F | M | A | M | J | J | A | S | O | N | D |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Temperature (°C) | 4 | 5 | 8 | 11 | 15 | 18 | 20 | 19 | 16 | 12 | 7 | 5 |
| Rainfall (mm) | 55 | 45 | 45 | 45 | 50 | 55 | 60 | 65 | 55 | 70 | 70 | 60 |
To draw it: (1) Draw the months along the bottom with equal gaps. (2) Add a rainfall scale (0 to 80 mm) on the left and a temperature scale (0 to 25°C) on the right. (3) Draw one bar for each month's rainfall. (4) Plot a point for each month's temperature and join the points with a smooth line. (5) Add a title and a key.
Annual temperature range: 20 − 4 = 16°C.
Total annual rainfall: 55 + 45 + 45 + 45 + 50 + 55 + 60 + 65 + 55 + 70 + 70 + 60 = 675 mm.
To describe it: Town P is warmest in July (20°C) and coolest in January (4°C). It is wet all year, with the most rain in October and November (70 mm each) and the least in February, March and April (45 mm each).
A flood hydrograph shows how the discharge of a river changes after a storm. Time goes along the bottom. Discharge, in cubic metres per second (m3/s), goes up the side. Rainfall is often drawn as bars at the top. Remember from Why Rivers Flood and What Floods Do that rain has to travel to the channel before the river rises. A hydrograph shows how long that takes.
Key terms:
Here is made-up data for a river after a storm.
| Hours after the storm began | 0 | 2 | 4 | 6 | 8 | 10 | 12 | 14 | 16 | 18 |
|---|---|---|---|---|---|---|---|---|---|---|
| Discharge (m3/s) | 10 | 10 | 25 | 70 | 130 | 80 | 45 | 25 | 15 | 10 |
Peak rainfall was at hour 4. Base flow is 10 m3/s. The rising limb runs from hour 2 to hour 8. Peak discharge is 130 m3/s at hour 8. The falling limb runs from hour 8 to hour 18, when the river is back at base flow.
Lag time = time of peak discharge − time of peak rainfall = 8 − 4 = 4 hours.
A short lag time, a steep rising limb and a high peak. Water reaches the river fast. This is common with steep slopes (water runs downhill quickly), impermeable ground such as concrete and tarmac (water cannot soak in, so it runs over the surface), saturated ground (it cannot hold any more water), little vegetation (less rain is intercepted), and heavy rain (more water arrives than the ground can take).
A long lag time, a gentle rising limb and a low peak. Water reaches the river slowly. This is common with gentle slopes (water runs downhill slowly), permeable rock and dry ground (water soaks in and moves slowly underground), thick vegetation (it intercepts rain and slows it), and light rain (the ground can take it all).
To draw a hydrograph, plot each discharge point and join them with a smooth line. Label the base flow, rising limb, peak discharge and falling limb, and mark the lag time with a double-headed arrow.
A kite graph shows how something changes along a line, such as a transect. Each type of plant gets its own horizontal line, with the same scale on each. At every point, the kite is drawn the same distance above and below its line, so its total width shows the amount, for example the percentage cover. Joining the marks makes a kite shape.
Key term: Kite graph: a graph that shows changes in amount along a transect, using a symmetrical shape for each item.
Here is made-up data for plant cover along a transect up a sand dune, in percentage cover.
| Distance from the sea (m) | 0 | 20 | 40 | 60 | 80 |
|---|---|---|---|---|---|
| Marram grass (%) | 10 | 40 | 30 | 10 | 0 |
| Red fescue grass (%) | 0 | 10 | 40 | 50 | 30 |
| Gorse (%) | 0 | 0 | 5 | 20 | 60 |
To draw it: (1) Draw three horizontal lines, one for each plant, all with the same distance scale (0 to 80 m). (2) Choose a width scale, for example 1 cm = 20%. (3) At each distance, mark half the width above the line and half below. At 40 m, marram grass is 30%, so mark 0.75 cm above and 0.75 cm below. (4) Join the marks to make a kite. (5) Label each line and add a key for the width scale.
To describe it: Marram grass is most common near the sea, peaking at 40% cover at 20 m, and it has gone by 80 m. Red fescue peaks at 50% at 60 m. Gorse is absent near the sea and increases to 60% at 80 m. The plants change from marram grass to gorse as you move inland.
A rose chart is a circular graph used for data with direction. A line points out from the centre for each compass direction. The length of each line, or the shaded petal around it, shows the amount. Rose charts are used for wind direction and for the direction that people walk.
Key term: Rose chart: a circular graph that uses compass directions to show how often something happens in each direction.
Wind direction is named by where the wind blows from. A wind from the south-west blows towards the north-east. Here is made-up data for the number of days in a 100-day period when the wind came from each direction.
| Direction | N | NE | E | SE | S | SW | W | NW |
|---|---|---|---|---|---|---|---|---|
| Days | 5 | 5 | 10 | 10 | 15 | 30 | 20 | 5 |
To draw it: (1) Draw eight lines from the centre, one for each compass direction, with north at the top. (2) Choose a scale, for example 1 cm = 5 days. (3) Draw each line to its length, so south-west is 6 cm and north is 1 cm. (4) Join the ends or shade the petals. (5) Add a title and the scale.
To describe it: The wind came from the south-west on 30 days out of 100, more than any other direction, so south-west is the prevailing wind. The wind was least often from the north, north-east and north-west, with 5 days each.
Climate graph: drawing rainfall as a line or temperature as bars, or forgetting the two scales. Hydrograph: measuring lag time from the start of the storm instead of from peak rainfall. Kite graph: drawing the kite on one side of the line only, so it is not symmetrical. Rose chart: showing the direction the wind blows towards instead of where it blows from. Any graph: no title, no units and no key.
Fig. 1.1 is a made-up table of data for the River Dell after a storm. Peak rainfall was at 3 hours.
| Hours after the storm began | 0 | 2 | 4 | 6 | 8 | 10 | 12 |
|---|---|---|---|---|---|---|---|
| Discharge (m3/s) | 5 | 5 | 20 | 60 | 35 | 15 | 5 |
(a) State the peak discharge of the River Dell. [1]
(b) Calculate the lag time. [2]
(c) Describe the rising limb of the hydrograph. [2]
(d) Suggest two reasons why a river in a built-up area might have a shorter lag time. [2]
(e) Describe what a climate graph shows and how its two parts are drawn. [3]
(a) 60 m3/s (1)
(b) Peak discharge is at 6 hours (1). Lag time = 6 − 3 = 3 hours (1).
(c) Discharge rises from 5 m3/s at 2 hours (1) to 60 m3/s at 6 hours, which is a steep rise (1).
(d) Any two: roads and roofs are impermeable so water cannot soak in (1); drains and gutters carry water quickly to the river (1); little vegetation to intercept rain (1).
(e) It shows the temperature and rainfall of a place for each month of the year (1). Temperature is drawn as a line (1). Rainfall is drawn as bars (1).
For lag time, write the two times and show the subtraction. Marks are given for the working as well as the answer.