the fire seem sudden but like most cases of wide fire its caused by factors which sometimes relate with climate conditions and sometimes bush burning. given that its summer, fire tends to spread much faster at this time of the year.
the effect of the widefire on the ecosystem cannot be understated given that the Amazon rain forest accounts for 20% of the oxygen the world consumes. its also home to some one million locals who have over time built a legacy in the amazon. science believe the forest is home to some new or even extinct species.

why they are happening is linked with the fact that fire spreads faster during summer.