How do we forecast weather for the world's agricultural crops and to divert natural disasters??

Question

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Answer 1

Generally agricultural outlooks (like seasonal outlooks as opposed to forecasts for the next few days to a couple weeks) are made by analyzing large scale, and long time period signals in the atmosphere.  El Nino/La Nina is a hugely important signal that is used to make seasonal forecasts.  If you are a farmer in northern Australia or maybe Indonesia, and there is an ongoing El Nino, then you can be 90% certain that you are going to get much less rainfall than normal.  If you are a farmer in Peru and there's an El Nino, you might plant rice instead of wheat, or drier weather crops because there should be moisture-a-plenty.

El Nino causes recognizable patterns worldwide, even in Africa which is very far from any direct El Nino abnormalities.

Similarly, in northwestern south America, El Nino tends to bring heavy flooding threatening people and property.  When they see an El Nino developing, they will expect flooding and take the appropriate steps to plan for a natural disaster due to flooding.

Answer 2

Natual disasters cannot be diverted.  You can't simply change their direction.   As for averting these disasters, only some forecasting will help.  For example, when there is to be a frost in Florida, growers may place smudge pots out to warm the area if a cold snap has been predicted.  Things like tsunalmi's and hurricanes you can't do much about.