I wonder if anyone has ever seen the Ritual Calling the Odious Drought cast in their ArM5 sagas. But it seems to me it's a joke of a curse, because it has no modifier for size, and thus only affects a patch of land up to 100 paces in diameter at most. It seems difficult to imagine that "streams dry up, and rivers dwindle" in the affected area as per the description.
It's actually a legacy spell, from 3rd edition, when Size was handled in an ad-hoc fashion: the basic spell (which was Level 40 rather than 50) affected all land within 1 mile of the caster, and you could increase that just by adding vis - an extra half a mile per pawn, so you could curse the entire Island of Man, for example. You could also make the Ritual Permanent for 8 extra pawns. I suspect nobody noticed the issue in the conversion because 5th edition nerfs large-scale Rituals (you have to pay all the extra magnitudes for Size, and they are always cast with a stress die, and D:Year is the longest they can generally last), so nobody seems to use them. Incidentally, I find this a serious design flaw in 5th edition.
I haven't used it, but I do have a Maga that might develop such a spell, probably with some Size magnitudes added. As it stands, it's good enough to use on a small farm, or a small keep.
My group never had any problems with spell levels back in the wild days of 2nd edition, and treat the highly regularized 5th edition system as strong, good guidelines, but just guidelines. The limits are important, but we need to leave room for magic.
I'd consider a 50th level ritual plenty for, say, a small valley or not-small estate. I'd allow a Permanent duration for extra vis and something like, say, a stone at the center of the effect that maintains the ritual as long as it stays dry. Never rained on ... But in 20 years a maiden despondant over the state of her grandfather's farm is going to shed tears on it ... Or in six months wandering priest is going to pray the drought away if the village doesn't ... Or the very next day a faerie's going to say, "Hey, free enchanted rock!" and make off with it. And that's all part of what makes it feel magical.
Working on the Grimoire we found lots of spells that were severely lacking in the needed Size to actually be effective. And I don't mean just in the spells we were reviewing for it, but also when we looked at published spells for comparison. Like a shocking amount of published spells that if you look at what they are "supposed to do" would be piss poor at it because they lack sufficient size.
Legacy spells are even worse since they are often horribly inefficient or missing mags because they try to target a specific level. Ether they could be done with a lower level (looking at you CtMT) because 5th is more efficient and so add extra or their effect is less efficient in 5th and you end up with a spell that "forgets" to include needed Mags to try to make level.