Perth's Climate Crisis by the Numbers: The Data Behind a City Running Out of Cool

Perth recorded its twelfth consecutive year of below-average rainfall in 2025, with the Bureau of Meteorology's Swanbourne monitoring station logging just 621 millimetres for the year — roughly 19 per cent below the long-term annual mean of 769 millimetres. That number, dry and unambiguous on a government spreadsheet, is the clearest single measure of how profoundly the city's climate has shifted since the mid-1970s.

The timing matters because WA's state budget, handed down in May, committed $2.1 billion to water infrastructure over four years, including expanded desalination capacity at the Binningup plant south of Mandurah. That spending decision is not abstract forward planning. It is the Cook government's acknowledgement that the Swan Coastal Plain can no longer rely on winter rainfall to fill the Integrated Water Supply Scheme, which supplies drinking water to 2.1 million people across metropolitan Perth and regional towns.

A City Heating Up, Neighbourhood by Neighbourhood

The urban heat data is granular and uncomfortable. The City of Stirling, one of Perth's most densely populated local government areas, commissioned thermal mapping in late 2024 that found surface temperatures in the Karrinyup and Balga precincts running up to 8 degrees Celsius hotter than adjacent bushland during summer afternoons. Stirling covers more than 99 square kilometres of predominantly low-canopy suburban streetscape, and its tree canopy cover sits at roughly 13 per cent — well below the 20 per cent threshold urban planners typically identify as the minimum needed to provide meaningful heat mitigation.

Meanwhile, the number of days per year when Perth exceeds 35 degrees has risen sharply. The Bureau of Meteorology's full dataset for Perth Airport — the city's primary weather reference point — shows the annual average of days above 35 degrees has climbed from about 29 in the 1960s to closer to 45 in the five-year period from 2020 to 2025. That is not a rounding error. For workers in construction and aged care, for students at schools without adequate shade structures along Wanneroo Road, and for households already spending heavily on electricity, those extra sixteen days carry real costs.

Western Power reported that residential electricity consumption across the South West Interconnected System — which covers Perth and the south-west — hit a new summer peak demand record in February 2026. Synergy, the state-owned retailer, processed a 34 per cent year-on-year increase in hardship applications in the first quarter of 2026, a figure that tracks almost precisely with the run of extreme heat events over that summer.

What the Numbers Mean for Infrastructure and Households

The Water Corporation's groundwater data compounds the surface picture. Monitored bores across the Gnangara groundwater mound — the vast underground reservoir that sits beneath the northern suburbs from Joondalup to Ellenbrook — recorded their lowest average level in recorded history during March 2026, dropping to 1.3 metres below the previous record low set in 2010. The Gnangara system once supplied roughly 45 per cent of Perth's drinking water. Today, desalination and treated wastewater recycling cover the majority of supply.

The State Planning Commission's draft Directions 2056 document, released for public comment in April, calls for mandatory 30 per cent green-space coverage in all new residential subdivisions approved after 2028. Developers working in growth corridors around Alkimos, Eglinton and Brabham are already lobbying against the requirement, arguing it conflicts with lot yield targets. The WA Planning Commission has not yet finalised the policy.

For existing homeowners, the Department of Energy, Mines, Industry Regulation and Safety calculates that retrofitting an average 1990s-era brick veneer house in the eastern suburbs — insulation, double-glazing, external shading — carries a median upfront cost of $18,500, with estimated annual energy savings of $1,200 to $1,600. At that rate, payback takes roughly twelve years. The state government's Household Energy Efficiency Loan Scheme offers interest-free loans of up to $15,000 for eligible owner-occupiers, though as of June 2026 the scheme had exhausted its initial $40 million allocation and a waitlist has formed. More funding has been promised but not yet legislated.

The numbers, taken together, describe a city making expensive, incremental adjustments to a climate that has already fundamentally changed. The question the data cannot answer is whether the adjustments are happening fast enough.