What caused the 2020 brushfires and the 2021 Aussie floodings
Lightning was the major cause of ignition of fires during the 2019–20 fire crisis in NSW and Victoria. The official NSW Bushfires Inquiry ((with advice from the NSW Rural Fire Service) concluded "Lightning, often in remote areas, started most of the bush fires that became very large, damaging and hard to suppress."
The NSW Bushfire Inquiry report found that, while thunderstorm activity was comparable to a normal year, lightning strikes were more likely to start a fire due to hot, dry conditions. Additionally, some fires became so large they generated Pyrocumulus clouds and dry lightning, sparking more blazes.
The Inquiry also noted a small percentage of fires started from human causes, (including powerlines, machinery and amateur back-burns on private rural properties) but that fires caused by suspected arson were a "very small proportion of the area burnt".
Further, ABC News reported arson was of little impact – accounting for around 1% of NSW fires and 0.3% of Victorian fires by 18 January 2020. The NSW Rural Fire Service referred numerous individuals to the NSW Police; 24 people were charged with arson, allegedly starting bushfires. Queensland police reported that 114 out of 1,068 fires "were found to be deliberately or maliciously lit".
I am not making anything up.
I'm really puzzled as to how you think vandals would cause floods. They are caused by very heavy rainfall in a short time that the rivers can't cope with. No one can make that happen.