I have an extensive background in agriculture and forestry with minors in engineering and chemistry. I grew up on a farm in Iowa where they do dry land farming. In a good year, the rains come at the right time in the right amount to produce good crops. I've seen years when you prayed that it would stop raining and 30 days later, you're praying for rain. I have experienced flood and sprinkler irrigation in the Blackfoot Idaho area.
Natural rainfall is ideal if it comes at the right time in the right amounts.
Since rainy seasons are of short duration in geographic locations, we have learned to build dams so we can store excess water in reservoirs for future use. Environmental issues are blocking the construction of new dams. Water rights are becoming a bigger issue every day. Water is becoming our most valuable resource. The overall cost will be the ultimate deciding factor.