Is it possible to create clouds by pumping water into volcanoes?
Is it possible to create clouds by pumping water into volcanoes?


Maybe, but it's a really bad idea. Here's why:


Volcanoes are unexpected and change with time. You can waste two years building a facility that does it, only for the volcano to cease being active and become dormant. Alternatively, the volcano might blow up and destroy your infrastructure.
You actually need lava to do so. Very few volcanoes have persistent lava lakes. Two are in tropical islands (Vanuatu, Hawaii), two are in rainforests (Nicaragua, DRC), one is in Antarctica, and only one is in a desert where it would actually be somewhat useful (Ethiopia).
In the absence of a lava lake, you can pump the water into the underground magma chamber and hope that it escapes in the form of steam. This is a bad bad bad idea, because you can cause a phreatic or phreatomagmatic eruption. Here's an example:


https://youtu.be/hjOnh_QRd0A


You need water. If you have fresh water, you better use that water to solve the drought directly instead of pumping it into a volcano. If you're using sea water, you have the problem of laze. At the moment the opposite is happening: Kilauea in Hawaii is erupting lava that reaches the ocean. The reaction between the hot lava and the sea water creates releases acid into the air. Bad idea. Here's how it looks like:


https://youtu.be/8SF5LQO4T_4


If somehow you managed to avoid exploding the volcano or creating acid rain, you would rapidly cool the top layer of the lava, solidifying it into rock. Rock is a poor thermal conductor, so you're forming a lid on top of the lava, making the thing much less effective.



  if an important effect of global warming is rainfall reduction and
  drought...(regardless of costs)


Just use desalination. A very effective yet expensive way to get fresh water.