How many gallons are in 1 inch of rainfall?

I just planted some banana and citrus trees and all the online guides I found talk about irrigation in inches per week... I'm going to be using drip irrigation and I need to know how many gallons a day, so how many gallons in 1 inch of rainfall?

How many gallons are in 1 inch of rainfall?
It depends on the space that you're talking about. If you put a cup out in the rain, and it rains only an inch, then there's only going to be an inch of rain in the cup. If you're talking about a bigger area, then it's proportionately more water, but it's also a bigger area to cover. If it rains an inch, or you irrigate an inch, they're the same thing (except that rainwater certainly works better).
Reply:Rainfall in inches is actually cubic inches. So, in a 1 acre plot (1 acre = 4,046.85642 square meters), 1 Inch of rain or 0.0254 meters would be:





4046 x 0.0254 = 102.78 cubic meters of water





1 (cubic meter) = 264.172051 US gallons





so 102.78 cubic meters = 27,000 gallons / acre / inch





I don't know enough about agriculture to sanity check this number, but I've included the steps so you can spot any mistakes.





Also, I'd be willing to bet that drip irrigation, being more efficient, would require a factor of magnitude less water.
Reply:Depends on the square feet of area you are watering. Figure it from there
Reply:Weather Bureau rainfall measurement simply means that at that station, there was enough rain to fill their measuring device to a level of one inch for the duration of that storm. So if you had a pan that has the dimensions of 1' x 1' it would have collected 144 cubic inches of water. The larger the collection dimensions - the larger the quantity of water collected. And you say, "Well - yah, duh." The point here is that the rain fall measurement is only relative to the RATE of rain that fell and does not have a direct bearing on the area upon which the rain fell except that AT THAT STATION, the RATE at which the rain fell accumulated one inch of depth in their collection device.





Now, rainfall RATE and irrigation volume differ. Irrigation VOLUME is a measurement of an amount of water to place into a planted area to satisfiy the water requirements of plants. The online guides you surveyed state X amount of water as a requirement for one week intervals. So one would place 1 inch of water in a field, or on a lawn, on the backyard garden etc. Now you also understand that there are all types of variables that influence just how much of the 1 inch depth of water will be available to the plants; daily tempreture (hot vs. cool weather), humidity effects evaporation rate, type of soil and its retention rate (sandy poreous vs. clay not very poreous), and the size of the plants (small - do not use as much water as larger). So that 1 inch amout of water requirement will change throughout the year. The 1 inch will change to more than 1 inch a week during warmer weather to consistantly satisfy the plants' need for water.





Now, you can go here for Tips on Watering Citrus:


http://www.ci.gilbert.az.us/water/Tipson...





and here for an expansion of the above, Irrigating Citrus Trees:


http://cals.arizona.edu/pubs/crops/az115...
Reply:That is a good question but more importantly would be what is the moisture content of the soil. There are many factors that involve rainfall to moisture content so buy a soil moisture meter and adjust your water accordingly.
Reply:Check out the site www.howstuffworks.com, lot's of interesting stuff on here!!! Type in IRRIGATION under search on their homepage and see what happens...