ENV242 Research Report Atmospheric Science PDF

Preview

Summary

Research Report...

Description

ENV 242 Atmospheric Science

Research Report

An Analysis of the extent and possible causes of Climate Change in the South-West Region of Western Australia between 1950 – 2019 Abstract The aim of this study is to analyse to which extent climate change is evident in the South West region of Western Australia (SWWA). Additionally, possible causes for the change in climatic conditions are investigated and discussed. Donnybrook and Pemberton have been chosen as geographical representatives. Meteorological data was obtained from the Bureau of Meteorology. The evaluation of the data revealed that climate change in SWWA causes a decrease in precipitation mostly evident in early winter rainfall and an increase in mean maximum and minimum temperatures. The cause for climate change in SWWA is understood to be a combination of factors, with natural climate variability, increase in atmospheric CO2 concentrations and land-cover changes being the most prevailing.

Introduction The climate is warming globally and in Australia. The Intergovernmental Panel on Climate Change (IPCC, 2019) reports a 1.0˚C increase in global temperature compared to preindustrial levels, which is a trend matched by Australia, for which the Bureau of Meteorology (BOM, 2020a) reports an increase of over one degree since 1910. The rise in temperature is accompanied by a decrease in precipitation, which, regarding Australia is especially apparent for Western Australia (WA) (IOCI 2002; Pitman et al., 2004; Hutfilter et al., 2019). These changes in climatic conditions are supposed to intensify with a progressively increasing global temperature of 0.2˚C per decade as a reaction to past and current greenhouse gas emissions (IPCC, 2019). The South West region of Western Australia (SWWA) extends over an area of approximately 24,000 km2 (Department of Primary Industry and Regional Development (DPIRD, 2017b), enclosed by latitudes ~32.5˚S and ~35.0˚S and longitudes ~114.5˚E and ~116.5˚E (Google, n.d.; Fig.1, Fig.2). The total population of SWWA in 2018 was 178, 406 (Australian Bureau of Statistics, 2020; Appendix 1), therefore being the most densely populated area outside of Perth (DPIRD, 2017b). The region is a popular tourism destination and an important agricultural and mining zone (DPIRD, 2017b). Moreover SWWA is one of the five internationally recognised biodiversity hotspots (Brouwers et al., 2012; Hutfliter et al., 2019), hence being home to a large number of endemic species under high levels of threat (English & Keith, 2015). A study by Brouwers and colleagues (2012) proposes landscape 1

ENV 242 Atmospheric Science

Research Report

fragmentation and climate change as two of the main threats to the SWWA biodiversity hotspot.

Figure 1. Map (top) of South West Western Australia defining areas of generalised land use (Department of Agriculture and Food, 2016). Map in right hand corner showing regional boundaries of the South West Region of Western Australia (Source: Department of Primary Industries and Regional Development, 2017b)

2

ENV 242 Atmospheric Science

Research Report

The aim of this report is to investigate the extent of climate change in the SWWA for the time period of 1950-2019. Furthermore the attempt is made to assign changes in the climate of SWWA to possible causes through the analysis and comparison of meteorological, atmospheric and land-use data. As a biodiversity hotspot and being home to a fast growing human population, the SWWA is very vulnerable to a changing climate.

Methods Two sites have been chosen, Donnybrook and Pemberton (Tale 1) to represent the SWWA. The sites have been chosen for their geographical location representing the southern respectively the northern half of the region, as well as for the availability of mostly continuous raw meteorological data from the Bureau of Meteorology (BOM, 2020b) for the time period of 1950-2019. Table 1. Descriptors of meteorological Stations in Donnybrook and Pemberton (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/).

Station No. 009534 009592

District Station Name Name Donnybrook South Coast Pemberton South Coast

Elevation

Longitude

Latitude

63 m 174 m

115.8247˚E 116.0433˚E

33.5719˚S 34.4478˚S

Current Status open

Mean annual rainfall data has been evaluated in 10 year intervals to be able to make statements of total percent increase/decrease in precipitation over the 70 year period, as well as to detect any fluctuations between the decades. Additionally, early winter rainfall (MayJuly/ MJJ) has been compared to late winter rainfall (August-October/ASO) to be able to identify any changes between the seasons. Similarly, mean annual maximum and minimum temperature data has been assessed in 10 year intervals to be able to identify any trends of an increase/decrease in temperature between 1950-2019. Furthermore, the frequency of months with a mean monthly temperature equal to or above 25˚C was determined, as well as the frequency of months with mean monthly minimum temperatures at or below 5˚C. And finally lowest minimum temperatures per decade for each site were recorded. As the climate of Australia is closely linked to the El Niño Southern Oscillation, data spanning from 1950 to 2019 for the Southern Oscillation Index (SOI) has been obtained from BOM and graphically analysed.

3

ENV 242 Atmospheric Science

Research Report

And lastly as a warming climate is understood to highly correlate with an increase in greenhouse gas emission (IPCC, 2019), CO2-e emission data for WA has been obtained from Australia’s Greenhouse Gas Emission Inventory System (Australia’s Greenhaus Gas Emissions Inventory System, 2019). For the time period of 1990-2017 total mean annual emission data has been evaluated in 5 year intervals.

Results Rainfall The analysis for the rainfall data reveals that average rainfall has decreased for both sites Donnybrook and Pemberton since 1950 (Fig. 2). When comparing the downwards trend of both sites, it becomes apparent that the fluctuations in rainfall data follow a similar pattern. Both sites have received an increase in rainfall between 1950-1969 and a sharp drop in the 1970-79 decade. All over the chart analysis suggests a negative linear trend, with Pemberton receiving significantly more rainfall than Donnybrook. 1300.000 1200.000 Mean Annual Rainfall (mm)

1100.000 1000.000 900.000 800.000 700.000 600.000 500.000 400.000 9* 01 -2 10 20

9* 00 -2 00 20

69

9* 99 -1 90 19

9 -1

9 98 -1 80 19

60

9 97 -1 70 19

19

9 55 -1 50 19

Time Period Donnybrook Pemberton

Linear (Donnybrook) Linear (Pemberton)

Figure 2. Bar chart representing of mean annual rainfall for Donnybrook and Pemberton in 10 year interval from 1950-2019. Error bars represent standard deviation, showing the variance of mean annual rainfall per decade. 10 year intervals marked with * indicate, that data was missing in the raw data set. For Donnybrook there was no data missing, for Pemberton these are the years 1999, 2006, 2011, 2015 and 2016 (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/).

4

ENV 242 Atmospheric Science

Research Report

Table 2 shows the variance in mean monthly rainfall numerically. Higher deviations indicate decades with higher discrepancy in mean annual rainfall levels. Table 2. Mean annual rainfall and standard deviation for Donnybrook and Pemberton between 1950-2019 (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/).

Period

Mean annual rainfall(mm) Donnybroo Pemberto k n

19501559 19601969 19701979 19801989 19901999 20002009 20102019

Standrard Deviation Donnybroo Pemberto k n

938.72

1206.21

114.24

221.69

1051.83

1238.89

203.51

194.38

928.87

1153.20

148.52

154.49

918.13

1115.90

131.29

161.91

948.67

1171.50

115.41

144.00

877.78

1197.58

147.54

141.72

857.46

1042.07

194.28

188.49

Table 3 shows the increase/decrease in rainfall per decade, as well as the overall decrease since 1950, which is 8.66% for Donnybrook and 13.61% for Pemberton. Table 3. Percent decrease/increase in mean annual rainfall per decade listed and overall decrease in annual rainfall between 1950-2019 shown in red . 10 year intervals marked with * indicate, that data was missing in the raw data set. For Donnybrook there was no data missing, for Pemberton these are the years 1999, 2006, 2011, 2015 and 2016 (Source: Australian Government Bureau of Meteorology). Period

Donnybrook

Pemberton

1950-1959 1960-1969 1970-1979 1980-1989 1990-1999* 2000-2009* 2010-2019* Total decrease 1950-2019

+12.05% -11.70% -1.16% +3.33% -7.47% -2.31% -8.66%

+2.71% -6.92% -3.23% +4.92% +2.23% -12.98% -13.61%

Furthermore, rainfall data for early winter and late winter month has been evaluated. Data for MJJ-rainfall for both sites show a similar negative trend, with a steep drop in average rainfall in the 1970-79 decade (Fig.3+4). The reduction in average MJJ-rainfall results in a 24.4% decrease for Donnybrook and an 18.8% for Pemberton (Table 4). In contrast Figure 3 and 4 suggest a positive linear pattern for both Donnybrook and Pemberton for ASO-rainfall. ASO5

ENV 242 Atmospheric Science

Research Report

rainfall for Donnybrook has increased by 9.04%. For Pemberton a rising trend is evident from 1950-2009, followed by a decline since 2010, resulting in an all over decrease of 0.2% (Table

Donnybrook Mean Early and Late Winter Rainfall (mm)

4). 250.000 200.000 150.000 100.000 50.000 0.000

Time Period Donnybrook Early Winter (MJJ) Donnybrook late winter (ASO)

Linear (Donnybrook Early Winter (MJJ)) Linear (Donnybrook late winter (ASO))

Figure 3. Graphical representation of early (May, June, July 9MJJ)) and late (August, September, October (ASO)) winter rainfall for Donnybrook in 10 year intervals between 1950-2019. Error bars represent standard deviation. (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/).

6

Pemberton Mean Ealry and LAte Winter Rainfall (mm)

ENV 242 Atmospheric Science

Research Report

250.000 200.000 150.000 100.000 50.000 0.000

Time Period Pemberton Early Winter (MJJ) Pemberton Late Winter (ASO)

Linear (Pemberton Early Winter (MJJ)) Linear (Pemberton Late Winter (ASO))

Figure 4. Graphical representation of early (May, June, July 9MJJ)) and late (August, September, October (ASO)) winter rainfall for Pemberton in 10 year interval between 1950-2019. Error bars represent standard deviation. 10 year intervals marked with * indicate, that data was missing in the raw data set., for Pemberton these are the years 1999, 2006, 2011, 2015 and 2016 (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/).

Table 4. The overall percent increase/decrease in early and late winter rainfall between 1950-2019 (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/).

Total % increase/decrease between 1950-2019 Early Winter (MJJ) Late Winter (ASO)

Donnybrook -24.4% +9.04%

Pemberton -18.8% -0.2%

Maximum Temperature The analysis of mean annual maximum temperature suggests a positive linear trend for Donnybrook and Pemberton for the time period of 1950-2019 (Fig. 5). Variances between mean monthly temperatures per decade are insignificant, which can be seen in the low values for standard deviation (Table 5). Both sites indicate a warming trend between 1950-1970, with a peak in the 1970-79 decade. In sum Pemberton seems to be warming faster than Donnybrook, with a ~2˚C rise for Pemberton since 1950 compared to ~1˚C for Donnybrook.

7

ENV 242 Atmospheric Science

Research Report

25.00 Mean annual max. temperature ( ˚C )

24.00 23.00 22.00 21.00 20.00 19.00 18.00 17.00 16.00 15.00

19

50

19 -1 9

59

60

-1 9

*

19 7 69

019

19 8 79

019

19 89

*

90

20 -1 9

99

*

00

20 -2 0

09

10

-2 0

19

Time Period Donnybrook Pemberton

Linear (Donnybrook) Linear (Pemberton)

Figure 5. Bar chart representing mean annual max temperatures per decade measured in degrees ˚C for between 19502019. Error bars are showing standard deviation. 10 year intervals marked with * indicate, that data was missing in the raw data set. For Donnybrook these are the years 1987 and 1989, for Pemberton these are the years 1951, 1987, 1989 and 1990 (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/).

Table 5. Mean annual maximum temperature (˚C ) and standard deviation for 10 year intervalls between 1950-2019 (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/).

Period

1950-1959* 1960-1969 1970-1979 1980-1989* 1990-1999* 2000-2009 2010-2019

Mean annaul max temperature (C ;)

Standard Deviation

Donnybrook Pemberton 23.24 19.68 23.03 19.84 23.47 20.18 23.24 20.1 23.29 20.86 23.45 20.85 24.16 21.57

Donnybrook 0.51 0.75 0.71 0.45 0.50 0.43 0.51

Pemberton 0.59 0.71 0.73 0.59 0.48 0.35 0.56

Usual mean maximum annual temperatures for Donnybrook and Pemberton are reported to be 23.1˚C and 20.4˚C respectively (BOM). Mean monthly temperatures of 25˚C or above can be regarded as unusually high for both sites. An analysis of the frequency of months with mean temperatures equal to or exceeding 25˚C suggests an increase in frequency of 15.91% for Donnybrook and 66.67% for

8

ENV 242 Atmospheric Science

Research Report

Pemberton (Table 6). Figure 6 shows that the increase in months at or above 25˚C increased rather

Frequency of month with mean temp. ≥ 25 ˚ C

steadily since 1980, after a steep drop between 1970-1980.

60 50 40 30 20 10

19

5

19 0-

0 * 59 19

6

19 0-

69 7 19

19 0-

79 8 19

8 19 0-

9* 19

9

9 19 0-

9* 0 20

20 0-

09 20

1

20 0-

19

Time Period Donnybrook

Pemberton

Figure 6. Line chart illustrating frequency of months per decade from 1950 to 2019 with mean monthly temperatures of 25˚C or higher. 10 year intervals marked with * indicate, that data was missing in the raw data set. For Donnybrook these are the years 1987 and 1989, for Pemberton these are the years 1951, 1987, 1989 and 1990 (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/).

Table 6. Frequency of months per decade from 1950 to 2019 with mean monthly temperatures of 25 ˚C or higher, as well as total percent increase. 10 year intervals marked with * indicate, that data was missing in the raw data set. For Donnybrook these are the years 1987 and 1989, for Pemberton these are the years 1951, 1987, 1989 and 1990 (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/).

Frequency of monthly temps equal to or exceeding 25 ;C Period Donnybrook Pemberton 1950-1959* 44 18 1960-1969 47 20 1970-1979 45 28 1980-1989* 37 13 1990-1999* 50 25 2000-2009 49 30 2010-2019 51 30 15.91% 66.67% % increase

Minimum Temperatures

9

Mean Winter Month Minimum Temp. (˚C)

ENV 242 Atmospheric Science

Research Report

9.00 8.00 7.00 6.00 5.00 4.00 3.00

Time Period Donnybrook Pemberton

Linear (Donnybrook) Linear (Pemberton)

Similarly, mean minimum temperatures for Donnybrook and Pemberton indicate a warming climate, evident in a positive linear trend since 1950 (Fig. 7). Calculations for standard deviation show that the variances of mean monthly minimum temperatures are in a tolerable range, with higher values for months with a more pronounced spread in monthly means (Table 7). An early peak in temperaturehighs can be recognised in the 1970-79 decade. The data for Pemberton shows an additional peak in the 1990-99 decade. In summary an increase in temperature of ~1˚C can be reported for Donnybrook and Pemberton (Table 7).

Figure 7. Bar chart representing mean winter month (June-August) minimum temperatures (˚C) for Donnybrook and Pemberton in 10 year intervals between 1950-2019. Error bars are showing standard deviation. 10 year intervals marked with * indicate, that data was missing in the raw data set. For Donnybrook these are the years 1979, 1986, 1987, 1989 and 2019 for Pemberton these are the years 1951, 1987- 1990, 2014 and 2015 (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/). Table 7. Mean winter month (June-August) minimum temperatures (˚ C) per decade and standard deviation for Donnybrook and Pemberton between 1950 and 2019. 10 year intervals marked with * indicate, that data was missing in the raw data set.

10

ENV 242 Atmospheric Science

Research Report

For Donnybrook these are the years 1979, 1986, 1987, 1989 and 2019 for Pemberton these are the years 1951, 1987- 1990, 2014 and 2015 (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/).

Period 1950-1959* 1960-1969 1970-1979* 1980-1989* 1990-1999 2000-2009 2010-2019*

Mean Winter Month Minimum Temps (˚C) Donnybrook Pemberton 5.88 6.41 6.48 6.60 6.30 6.19 6.78

6.99 7.40 7.53 7.47 7.81 7.55 7.74

Standard Deviation Donnybrook Pemberton 1.00 0.82 0.73 0.82 0.49 0.33 1.13 0.88 0.94 0.37 0.73 0.37 0.78 0.76

The analysis of the frequency of months with mean temperatures at or below 5˚C reveals a significant reduction since 1950. There is no evidence of months with average temperatures at or below 5˚C in Pemberton since 1960 and for Donnybrook the frequency dropped by 80% (Table 8). Additionally, Table 8 provides evidence that the lowest minimum temperatures measured per decade are rising, resulting in an increase of ~1˚C for Donnybrook and Pemberton. Table 8. Quantity of mean monthly minimum temperatures at or below 5 ˚C and lowest minimum temperature measured for Donnybrook and Pemberton per decade between 1950-2019. 10 year intervals marked with * indicate, that data was missing in the raw data set. For Donnybrook these are the years 1979, 1986, 1987, 1989 and 2019 for Pemberton these are the years 1951, 1987- 1990, 2014 and 2015 (Source: Australian Government, Bureau of Meteorology: http://www.bom.gov.au/climate/data-services/).

Period 1950-1959* 1960-1969 1970-1979* 1980...