There is some good research out there to show that tree do increase rainfall, at least as a local redistribution effect. I recall a study some years back comparing the rainfall either side of one of those fences(rabbit proof, emuproof, dingo proof?) where the vegetation was seriously reduced on one side. The study found a dramatic reduction on the lower vegetation side.
It occured to me at lunch that trees are water neutral to slight sinks (when growing they use up water), something that crt and I have discussed at length, so the question then is exactly what effects might cause the increase in rainfall. One possibility is that the trees increase the local humidity by pumping groundwater and that leads to higher rainfall. This effect is almost certainly relevant in areas such as Merredin, whose ground water has risen precipitously as a result of growing shallow rooted annuals such as wheat.
Another effect is the increased turbulence and cloud catcher effects where the rapid stirring of air, combined with radiatively cooled leaves increase dew. Also, trees increase albedo, perhaps encouraging updrafts. I don't know, perhaps someone can educate me.
I checked the greenhouse after I got home and noticed that some of my alpine craspedias were looking a little droopy. The soil thermometer registered 40C and the soil was bone dry. Further investigation found sad herbs, droopy pot plants and sad plants I had only just planted. Turns out that the watering system's blown a fuse on the low voltage side.
I replaced the fuse with a screw, as despite having around 50 standard sized fuses and car knife fuses, I didn't have a single 3mm fuse. I guess I need to go shopping on the weekend.
Also sad was a rare plant I'm growing in my hanging creek. Not sure what the problem is, might be overheating. It is sitting in a stream of water as per its natural environment, so it's not a lack of water that is the problem.