The terminal velocity of water is going to be reached when the water encounters drag equal to the weight of its mass. A flat sheet of water would have substantial weight- at 2” depth, just 2 square feet of water would weigh about 21lbs. without calculating the speed of impact- at an initial fall rate of “9.8” m/s2 at the height of a rain cloud- even large rain drops can carry enough force to cause soil erosion. So this sheet of rain would theoretically be quite destructive- likely fatal.
We are missing the forrest through the trees here.
If water fell in a solid sheet- we might not be alive to even be hit by the water. The properties of water make it so that water won’t really stay together like that. If you dump a cup of water- the water doesn’t stay in a cylinder shape like the cup as it falls does it? But the interaction with air, air pressure, the differential in force over the entirety of the sheet- picture a sheet of wood- if you push up hard on one side, and down hard on the other- even wood won’t stay in a solid sheet and will split.
So one of the factors that could allow water to fall in solid sheets would be an almost “vacuum” like state where there was no air or air pressure below it. If every time a cloud passed overhead, all the oxygen was sucked out of the area below the cloud- you’d die from hypoxia before the rain could kill you. Likewise- most of the ways would could alter rain so that a 2” thick sheet of several square miles size could maintain integrity as it fell to earth, would likely either may the water much more “solid” and even more dangerous than water as is- or would require quantum phenomenon that would make the water almost weightless so that the 2” sheet would be more like vapor.
Now- if we mean 2 SOLID inches of water- water molecules so tightly packed together that the entirety of those 2” are water... that’s going to be more akin to ice (unless you pack the molecules so tight as to form some sort of gravitational singularity or nuclear reaction- which would have its own dangers defined the weight of the water.) And obviously a solid 2” sheet of ice dropped from thousands of feet would mess shit up. Of course... the ice probably wouldn’t stay in a sheet.... and around we go.
The physics aren’t really there- so how this would turn out depends upon some unspecified variables and some assumptions. Probably badly though. Take for granted that the causes of and effects of a 2” sheet of water the size of a cloud would probably not be good.
It would be a lot worse than a 2 inch sheet..
If water fell in a solid sheet- we might not be alive to even be hit by the water. The properties of water make it so that water won’t really stay together like that. If you dump a cup of water- the water doesn’t stay in a cylinder shape like the cup as it falls does it? But the interaction with air, air pressure, the differential in force over the entirety of the sheet- picture a sheet of wood- if you push up hard on one side, and down hard on the other- even wood won’t stay in a solid sheet and will split.