Why is it getting less rainfall, you'd ask if you weren't dedicated ideologically-motivated deniers? This is why:
The decline in autumn and winter rainfall in the south-west is attributed to the southward shift of the subtropical ridge and the southern hemisphere polar jet stream (YouTube SW May–October rainfall animation). The associated strengthening of the polar jet stream and a 17% reduction in the strength of the subtropical jet stream over Australia has reduced the likelihood of storm development over the south-west. This is most likely the result of a weakening of the temperature gradient between the equator and the poles.
A weaker subtropical jet stream leads to slower alternation of low and high pressure systems, and weaker surface low pressure systems and cold fronts. The stronger polar jet stream is associated with low pressure anomalies over Antarctica and high pressure anomalies over the mid-latitudes. Consequent rainfall reductions over south-west WA are associated with the persistence of high pressure systems over the region. While heavy rainfall events can still occur, they are often interspersed by longer dry periods.
Of course this stuff just bounces off the old lead headgear of stone-age Right-wing ideology with you lot. Most information does not penetrate, and that which does must conform to the dogma.
