Microclimatic Hazards and Change

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IB Geography Internal Assessment HLNovember 2010

Climatic Hazards and Change- Microclimate -

St. Peters Lutheran CollegeMs. T. Dowell

Candidate Name: Pei-Han Sabrina WongCandidate Number: 003063-040

Word Count: 2464

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Contents:

1. Introduction - 2-

2. Methodology- 5

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3. Results and Analysis - 7-

4. Conclusion -12 -

5. References -13 -

6. Appendix -14 -

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Introduction:

The aim in this microclimate investigation is to measure differences intemperature and relative humidity in the lower atmosphere caused byman-made and natural ground surfaces at a micro-level in Brisbane, StPeters Lutheran College.

It is hypothesised that:Natural ground surfaces produce cooler and more humid air within theimmediate vicinity (microclimate) than man-made surfaces.

In which, the hypothesis is split into two categories:

1. It is postulated that man-made surfaces such as concrete andbitumen have varying effects on microclimate where concrete ismore conducive to producing a cooler and less humidenvironment; and

2. It is also expected that natural ground surfaces such as exposed

soil will produce much hotter and less humid environment thansheltered soil.

This investigation is carried out to understand the variations oftemperature and humidity caused by the surfacing on the ground. Theresults of this project are able to provide a better understanding of thedetails of the lower environment (a foot above ground). It would alsoprovide a number of useful purposes for people such as engineers andlandscapers; more cautious in the selection of suitable materials orstructural design to reduce heat effects.

The surface atmosphere is extremely unpredictable and is affected by thewind and humidity. The active movement in the zone between ground andair is one of the major reasons that cause such variations. Furthermore, amicroclimate is easily affected by external influences such as the surfacecolour, moisture, vegetation and aspect of the current site 1,2. Therefore,the data collected is expected to vary between the different sites, asstated in the hypothesis using a thermo-hygrometer.

In this investigation, there are four different ground surfaces to beexperimented on; concrete and bitumen to represent man-made surfaces,in addition with sheltered soil and exposed soil for natural surfaces. Below,Figure 1, shows the general area where the experiment will take place in

Brisbane, Australia; the red shaded area represents St Peters LutheranCollege. The following image, Figure 2, shows the specific region of whereeach ground surfaces are located within the college.

1D.J. Briggs and P. Smithson, "Micro and Local Climates." Fundamentals ofPhysical Geography. London: Rowman & Littlefield, 1986, 133-151, Print.2

B. Ponn, "Pavement Albedo." Heat Island Group. N.p., 30 June 1999,

Web, 27 Aug. 2009..

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Figure 1 A map of the study location3,4

The sites we visited are shown in Figure 2; bitumen is located at Rainforest

Drive, with a north-western aspect. The concrete surface is positioned infront of the Chapel, with a western aspect. Sheltered soil is situated inRainforest Reserve with an abundant amount of tall vegetation as shelter,whereas the exposed soil is near College Drive, without any source ofshade. Results would not be biased between sites because of the relativeequal air flow rates and elevation, as well as negligible breezes or wind-channels.

3J. Platt, "OZ's endangered species." 60-Second Science Blo,.Scientific American Inc., 28 May 2009, Web, 27 Aug. 2009..4 St Peters Lutheran College, Brisbane: n.p., 2008, N. pag, Print.

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Figure 3 Interpretation of Spearmans Rank Correlation Coefficients

The sensors used in this experiment were unable to read humidity levelsthat were lower than 20% and the result of this is when the screen showsLO instead. To resolve this predicament, the humidity of LO was replacedwith 18%. This was done to provide actual values to create tables andgraphs.

Finally, all the data collected was collaborated and graphed against eachother. The following results and analysis describes the findings of ourexperiment.

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Results and Analysis:

Figure 4 summarises the mean averages of temperature and humidityreadings of different surface types calculated from processing the rawdata obtained from the many sites:

Figure 4 Mean average temperature and humidity by surface types

Sheltered SoilAverages Day One Day Two Day Three Mean Average

Temperature(C) 23.33 20.87 24.52 22.91

Humidity (%) 49.33 49.83 32.33 43.83

Exposed SoilAverages Day One Day Two Day Three Mean Average

Temperature

(C) 29.25 27.37 29.54 28.72

Humidity (%) 38.67 22.17 18.00 26.28

BitumenAverages Day One Day Two Day Three Mean Average

Temperature(C) 31.12 29.58 34.94 31.88

Humidity (%) 30.83 30.33 18.00 26.39

ConcreteAverages Day One Day Two Day Three Mean Average

Temperature(C) 30.50 30.80 32.96 31.42

Humidity (%) 23.67 26.67 18.00 22.78

Briefly looking at the averages calculated we can see that the shelteredsoil site has the highest humidity levels and lowest temperature. We canalso observe that the concrete site has the lowest humidity levels,whereas the bitumen site has the highest temperature. From this simpleobservation, the tables illustrate that natural surfaces are much cooler andmoist compared to man made surfaces.

Using the mean averages of the different sites, the data collected can befurther processed into graphs. By drawing a scatter graph and trend lines,a correlation can be easily distinguished from the many data attained.Below, Figure 5 illustrates an inverse relationship between the humidityand temperature, thus proves the simple concept of relative humidity thatthe atmosphere can to hold more water vapour with decreasingtemperatures:

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Relationship between Temperature and Humidity

0

5

10

15

20

25

30

35

40

45

50

20 22 24 26 28 30 32 34

Temperature (C)

Humidity(%)

Figure 5 Inverse relationship between temperature and humidity

A significance test, as defined by the formula below, is used to indicatewhether the results are reliable:

where:

di = the difference between the ranks of the corresponding values

in both data; andn = the number of samples in each data set (same for both sets).

[6]

Applying this to the four sites, the four outcomes can be generated whichthen can be plotted against the Spearmans graph, the following are theresults:

Sheltered soil:

Concrete:

Bitumen:

Exposed Soil:

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Figure 6 The significance of the Spearmans rank correlationcoefficients and degrees of freedom 6

By calculating the significance of Spearmans rank correlation coefficientswe are able to confirm with higher confidence that the correlation did nothappen by mere chance. The sheltered soil, concrete and bitumencoefficients are all above 0.6, suggesting a fairly strong positive

correlation. However exposed soil has a value of 0.11, displaying that thedata between humidity and temperature within the old playground (thesite of exposed soil) has low to no correlation. Using the calculated values,the significance of the relationship can be discovered. Referring to Figure6, it is apparent that the results taken from sheltered soil, concrete andbitumen all go over the 5% red line. This illustrates that those results onlyhave a rejection level of 5%, and the correlation is 95% reliable-theoutcomes can be considered to be accurate. However, the data of exposedsoil provided a correlation lower than the 95% dependability, implying thatthe rejection level is relatively high.

6

"Spearman's Rank Correlation Coefficient." Barcelona Field StudiesCentre. N.p., 2009. Web, 27 Aug. 2009..

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Displayed below is Figure 7 which shows the relationship betweenhumidity and temperature in a scatter graph. The use of the scatter graphprovides a much easier understanding and effective image upon theobtained data, as it explores the relationship between the two variables.

Average Temperature and Humidity of Different Surfaces

0

5

10

15

20

25

30

35

40

45

50

Sheltered Soil Exposed Soil Bitumen Concrete

Temperature (C)

Humidity (%)

Figure 7 Average Temperature and Humidity of Different Sites

The bar graph is able to effectively prove the hypothesis that naturalground surfaces produce cooler and more humid air within the immediatevicinity than artificial ground surfaces. Using the bar graph, it shows thatsheltered soil and exposed soil (natural surfaces) indeed have lower

temperatures than bitumen and concrete (man-made surfaces). In Thegraph also illustrates that the natural surfaces also have higher humidityrates compared to artificial surfaces. Moreover, the addition of linear trendlines emphasizes the inverse correlation for humidity and directcorrelation for temperature.

Generally looking at Figure 7, man-made surfaces do not provide suchsignificant results, as their differences are not significant. Although thereis only 0.20C temperature difference and 3.61% humidity difference,there is still a reason behind the variation. Bitumen produces an averageof 31.88C temperature and 26.39 % humidity compared to the 31.42Cand 22.78% measurements taken from concrete. Therefore, bitumen

fabricates slightly warmer temperature and higher humidity.

For man-made surfaces, the temperature of the vicinity can be caused bythe albedo. Albedo, is an important concept in climates, it is thepercentage that the surface reflectivity of the suns radiation. The averagealbedo of concrete is 55% which is 4.5 times the amount of bitumen. Asthe albedo decreases, more sunlight is absorbed and thus the temperaturenaturally increases7. Using this secondary data, it supports the collecteddata that bitumens temperature is slightly warmer due to the low albedopercentage compared to concrete. In addition, the bitumen and concretesurfaces had different exterior colours to it, the bitumen was black and

7B. Ponn, "Pavement Albedo." Heat Island Group. N.p., 30 June 1999, Web,27 Aug. 2009. .

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concrete was white. This then suggests that bitumen absorbed moreradiating heat compared to concrete because of the surfaces colour, dueto the common knowledge that black absorbs more heat in comparison tolighter colours.Observing from Figure 7, sheltered soil shows a major difference, as it ismuch cooler and much moist, compared to exposed soil which thenestablishes that exposed soil is warmer and more arid than sheltered soil.

For natural surfaces, as the soil is darker in colour, it is able to absorbmuch more radiant energy than lighter coloured soils. In addition to that,moisture has a larger heat capacity, thus moist soil warms up slower thandry soil. As trees absorbs more radiation and transpires moisture in air,the vapour pressure is higher in forests than a non-vegetated region.Since air is a poor conductor of heat, dry sandy soil is able to getexceedingly hot as there are lots of air vacuoles present, and thus heattransfer is slow and heat is trapped in the upper layers8. This can beillustrated with the Figure 8:

Figure 8 Effects on Temperature against Different Soils [7]

Comparing natural surfaces to man made surfaces, natural surfaces havevegetation to block out a certain amount of radiation that would normallyreach the ground. They transpire and have low heat capacity, thus resultsto cooler temperatures and higher humidity9. However, man madesurfaces such as bricks, concrete and stones, all have high heat capacitypermitting them to store large amounts of heat. In addition, man made

surfaces do not have any vacuoles for water to be absorbed; therefore, ithas a lower humidity10.

The patterns that have occurred in the graphs clearly confirms the directrelationship between temperature and relative humidity as thetemperature within the area is low, more moisture is held in the

8D.J. Briggs and P. Smithson, "Micro and Local Climates." Fundamentals ofPhysical Geography. London: Rowman & Littlefield, 1986, 133-151, Print.9D.J. Briggs and P. Smithson, "Micro and Local Climates." Fundamentals ofPhysical Geography. London: Rowman & Littlefield, 1986, 133-151, Print.10

B. Ponn, "Pavement Albedo." Heat Island Group. N.p., 30 June 1999,

Web, 27 Aug. 2009..

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immediate atmosphere. The graphs also demonstrate that naturalsurfaces generate lower temperatures and higher humidity rates.

To an extent, sheltered soil can be considered to be an anomaly, as theestimated value on the graph should be where the line indicates 0.5,instead the temperature is comparatively lower and the humidity is higher.However, the results for exposed soil must be acknowledged to beunreliable due to its lack of correlation.

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impact on the results and overall have proven the hypothesis and sub-hypothesises correct.

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Bibliography:

[1] D.J. Briggs and P. Smithson, "Micro and Local Climates."Fundamentals of Physical Geography. London: Rowman & Littlefield,1986, 133-151, Print.

[2] B. Ponn, "Pavement Albedo." Heat Island Group. N.p., 30 June 1999,Web, 27 Aug. 2009..

[3] J. Platt, "OZ's endangered species." 60-Second Science Blo,. ScientificAmerican Inc., 28 May 2009, Web, 27 Aug. 2009..

[4] St Peters Lutheran College, Brisbane: n.p., 2008, N. pag, Print.

[5] "About Us." St Peters Lutheran College. N.p., 2009, Web, 27 Aug.2009. .

[6] "Spearman's Rank Correlation Coefficient." Barcelona Field StudiesCentre. N.p., 2009. Web, 27 Aug. 2009..

[7] Fundamentals of Physical Geography, By D. J. Briggs and P. Smithson,London: Rowman & Littlefield, 1986, 558, Print.

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Appendix:

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Microclimatic Hazards and Change

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