Will rain affect the growth of crops?

Solution 1:

The code that determines the rate of growth is:

getGrowthRate(crop)
{
    if (crop.getBlockBelow().isHydrated())
        growthRate = 4.0;
    else
        growthRate = 2.0;

    for (farmland in crop.getFarmlandIn8BlocksBelow()) //Immediately surrounding Farmland with crops
    {
        if (farmland.isHydrated())
            growthRate = growthRate + 0.75
        else
            growthRate = growthRate + 0.25
    }

    if (crop.hasNeighborCropOnNS() and crop.hasNeighborCropOnEW()) //If (north OR south) AND (east OR west) have crops
        growthRate = growthRate / 2;
    else if (crop.hasNeighborCropDiagonally()) //If any immediately diagonal square has a crop
        growthRate = growthRate / 2;

    return growthRate;
}

isHydrated() returns whether a farmland block is moistened or not. Rain does not make farmland moist any quicker than normal.

So the answer is no, rain does not affect the rate of growth of crops.