"When there is a long drought and then heavy rains causing floods- is there an impact on the drought? Do things green up and grow? Or does flooding strip the topsoil?"

The simple answer is "Depends".

While some areas right under the biggest flood flow force will have a degree of stripping, when the flow slows a bit, it starts to dump the spoil. As soon as the water clears, things green up - grass will grow several inches in a few days, especially with the sun out. So there may be patches of erosion among lush plant growth.

Drought will strip topsoil far more devastatingly, as there is nothing to hold the soil.

Millions of years of evolution here have caused plants and animals to cope - West Australia regularly runs 'Flower Tours' to show the regrowth after drought breaking rain - you would not believe the ravishing solid spread of intermixed color where a week before there was only dry sandy soil. Animals appear from apparently nowhere (where they all hide is still not really understood), especially small ones.

Kangaroos can have a joey at foot, one in the pouch, and one in the womb. When it rains, the one in the pouch is kicked out, she gives birth, then immediately breeds. The one in the womb can go into stasis for quite a while until conditions improve. I'm surprised that the RC Church has not adopted the roo as their emblem ...