People can fly planes into the air and release chemicals into the air if they really need the rain and sometimes a storm will form. Increase in pollution can because all the gas and chemicals that come off the pollution will go into the ozone layer and cause an increase in moisture which could cause rain clouds to form. One last thing is evaporation, condensation, and precipitation. Plants absorb water and moisture then it would evaporate into the air which would form rain clouds, then the rain clouds would have rain in them and then rain would fall out of the clouds.