It is classified as hot desert in the northern and continental areas and hot grasslands in the northwest. In the Pilbara, temperatures rose most in winter and spring and cooled in autumn and summer. Annual rainfall increased over much of the Pilbara, except in the west where it decreased.
These changes include a southward shift in the subtropical ridge and the Southern Hemisphere westerly jet stream. There is high confidence that potential evapotranspiration will increase, but only medium confidence in the magnitude of the change. This bulletin is one of the Pilbara Hinterland Agriculture Initiative (PHADI) report series and provides a general description of the climate in the Pilbara region of Western Australia and the main climate drivers.
According to the Köppen system, the region is classified as hot desert in the northern and interior areas and hot grassland in the north-west (Figure 2.1).
Temperature
During winter, average temperatures throughout the region are around 20°C and minimum temperatures are significantly lower than at other times of the year, especially in higher elevation and southern inland areas (Figure 2.2 and Figure 2.3). Coastal areas have a smaller annual temperature range compared to inland areas (Figure 2.3) and winter temperatures rarely fall below 10°C. Frost is only a risk in the high elevations of the Hamersley Ranges and the extreme southeast of the region (Figure 2.4).
Mardie Onslow Airport Year CP CH CP CH CP CH CP CH CP CH CP CH. Cumulative chilled fractions (per year) estimated using the University of California spreadsheet available at ucanr.edu/sites/fruittree/How-.
Rainfall
The Pilbara has the second largest inter-annual variation in rainfall in Australia, after central Australia (Charles et al. 2015). This variability is seen at all the sites shown in Figure 2.6, where mean rainfall significantly exceeds the median in most months, reflecting the heavy rainfall received in some years (90th percentile). TCs are responsible for most of the extreme rainfall events and generate 25–34% of the total annual rainfall near the Pilbara coast and as much as 21% up to 450 km inland (Charles et al. 2015).
The contribution of precipitation from other events, such as tropical depressions and convective storms, accounts for the rest of the summer precipitation total (Charles et al. 2015). The interannual and spatial variability of TK strongly affects their reliability as a source of water supply (Bates et al. 2012, Charles et al. 2015).
Evaporation
Solar radiation
However, northwesterly cloud bands can bring rainfall when a trough of low pressure occurs in the upper levels of the atmosphere, or warm, moist tropical air originating over the Indian Ocean moves southward. In summer, the ridge moves south, causing the monsoon to develop in the far north. The Indian Ocean Dipole (IOD) - quantified as the difference in ocean temperatures in the western and eastern Indian Ocean - and the El Niño Southern Oscillation (ENSO) index - quantified as differences in atmospheric pressure across the Pacific Ocean - can act individually or interact have to influence tropical cyclone activity and rainfall over northern Australia (Charles et al. 2015).
The subtropical ridge is a belt of high pressure that encircles the globe at mid-latitudes. The monsoon contributes to rainfall over the Pilbara, but more in the east than in the west (Charles et al. 2015). TCs heading south of about 22°S or crossing the coast of Pilbara tend to curve and accelerate southeast.
TCs crossing the Pilbara coast tend to move further inland than in other parts of Australia. Historically, TCs have caused significant damage and loss of life in the Pilbara, but modern design regulations mean that buildings and other infrastructure are now much less susceptible to damaging winds (BoM undated 4). They form between March and October when warm, moist tropical air from the Indian Ocean moves southeast and rises above colder air in mid-latitudes (BoM 2013).
The influence of the Indian Ocean is generally quantified using the IOD, which is the difference in SST anomalies between the western and eastern Indian Ocean. The term El Niño refers to the negative phase of ENSO when SST in the central and eastern tropical Pacific Ocean is warmer than average, while La Niña is the positive phase of ENSO when SST in the central and eastern tropical Pacific Ocean is cooler than average (BoM 2011a and b). El Niño and La Niña events usually last about a year and tend to start in the fall, mature in the winter, spring, and early summer, then begin to decline in late summer and end in the fall.
Rainfall
Temperature
Evaporation
Tropical cyclones
The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (IPCC AR5) concluded that there is very high confidence (Appendix D) that more than half of the observed increase in global temperature is caused by human activities that increase greenhouse gas concentrations in the atmosphere increased ( Bindoff et al. 2013 ). As global temperature increases, the hydrological cycle intensifies and atmospheric circulation patterns change so that the tropical belt widens, and storm tracks and. The latest climate projections for the northern Australian Rangelands, which includes the Pilbara, conclude that there is high confidence that temperatures will do so.
The following sections describe possible changes in Pilbara climate up to the end of this century. This information summarizes data from: BoM; the Indian Ocean Climate Initiative (IOCI) Phase 3 (Bates et al. 2012); CSIRO and BoM (2007), which used emissions scenarios and global climate models (GCMs) associated with the IPCC Fourth Assessment Report (IPCC AR4); and Charles et al. 2015 ), which used emissions scenarios for Representative Concentration Pathways (RCP) and Coupled Model Intercomparison Project Phase 5 (CMIP5) GCMs associated with IPCC AR5. Appendix B provides a brief description of the various emission scenarios and some of the limitations of the climate modelling.
CSIRO and BoM provide a comprehensive discussion of the sources of uncertainty around climate modeling and how to assess and use the data.
Temperature
The intensity and duration of hot spells may increase in most of the region, while the frequency may decrease (Figure 5.2). While climate models have difficulty reproducing observed frost occurrence, frost frequency is predicted to decrease with increasing temperature (CSIRO & BoM 2007, Watterson et al. 2015).
Rainfall
CSIRO & BoM (2007) suggest that the number of dry days is likely to increase, while Kirono et al. 2011) suggest that the extent and frequency of drought will not change significantly. 2015) concluded that there was low confidence in projections of the frequency and duration of extreme drought (when the Standardized Precipitation Index, SPI, is -2 0r less, CSIRO& BoM 2015) may change, but medium confidence that the duration of droughts will increase throughout the century for RCP8.5. It is widely agreed that rainfall intensity - the amount of rain that falls in a day. confidence that the intensity of heavy rainfall would increase, but there was low confidence in the magnitude of the changes.
2015) suggest that if current trends for a poleward shift in the global circulation continue and intensify, summer and autumn rainfall may increase over northwestern Australia.
Tropical cyclones
Wind speed
Evaporation
Fire risk
This is to deal with uncertainties arising from the internal variability of the oceans and atmosphere, and from limitations in the ability of models to simulate all processes in sufficient detail. The 90th percentile projections were within ±10% and the 10th percentile were within ±59% of the measured values for all sites except Mount Vernon (±191%). Indian Ocean Climate Initiative Phase 3 Downscaled Climate Projections for Western Australia, data.csiro.au/dap/landingpage?pid=csiro:5266.
Evolution of the Southern Annular Mode Over the Past Millennium', Nature Climate Change, vol 4, pp. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UK and New York, New York, USA. Bureau of Meteorology (BoM) undated 1, 'Tropical Cyclones Affecting Pilbara', viewed November 2014 bom.gov.au/cyclone/history/wa/pilbara.shtml. undated 2, “Tropical Cyclones Affecting Port Hedland,” viewed November 2014 bom.gov.au/cyclone/history/wa/pthed.shtml. undated 3, "Climatology of Tropical Cyclones in Western Australia", viewed November 2014 bom.gov.au/cyclone/climatology/wa.shtml. undated 4, 'Tropical Cyclones Affecting the Karratha/Dampier/Roebourne region', accessed November 2014. bom.gov.au/cyclone/history/wa/roebourne.shtml. 2005, 'Climate Classification of Australia', viewed November 2014 bom.gov.au/jsp/ncc/climate_averages/climate-. classifications/index.jsp?maptype=kpn.
2012, 'The Madden-Julian Oscillation' viewed October 2014, bom.gov.au/climate/about/?bookmark=mjo. 2013, 'Northwest cloudbands' viewed November 2013, bom.gov.au/climate/about/?bookmark=nwcloudband. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press. 2015, Climate Change in Australia Information for Australia's Natural Resource Management Regions: Technical Report, CSIRO and Bureau of Meteorology, Australia, viewed January 2015,klimachangeinaustralia.gov.au/en/.
Kossin, JP, Emanuel, KA & Vecchi, GA 2014, 'Poleward migration of the location of maximum tropical cyclone intensity', Nature vol. 2010, Guidance Note to Lead Authors of the IPCC Fifth Assessment Report on Continuing Uncertainties, Intergovernmental Panel on Climate Change (IPCC). Northern Monsoon Cluster Report, Australian Climate Change Projections for Australia's Natural Resource Management Regions: Cluster Reports, CSIRO and BoM, Australia. http://www.climatechangeinaustralia.gov.au/en/publications-library/. 2000, Special Report on Emissions Scenarios: a special report of Working Group III of the Intergovernmental Panel on Climate Change.
Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Regional Development Australia Pilbara 2013, Pilbara State of the Environment Report 2013, Regional Development Australia Pilbara, viewed November 2014,.
