Early in the monsoon season followup rains are unlikely after the initial downpour is spent. This changes rapidly as the monsoon season advances. At other times of year the probability of followup rains are totally unpredictable. After a few years of drought the ground will be able to absorb huge amounts of rainfall before serious flooding occurs. In wetter years washes may run heavily with very little rain.
Natural indicators show severity and extent of past floods.
The debris left from a flood hangs in the brush for a very long time. Even should brush leveled by strong water recover to an upright position, the debris caught in it would serve as an alarm of previous high water. If flood debris is hanging in the brush above the present water level, you can be sure that water will reach that high again. Many have needlessly died attempting river rescues. Generally this can be attributed to a lack of awareness of both the risks involved, and the procedures for managing those risks.