In the troposphere, the temperature of the atmosphere descends with altitude. Therefore the clouds in the troposphere are lower in temperature as they rise in altitude and vice versa. When the temperature of a cloud is above 0 °C, the cloud is called a warm cloud; when it is below 0 °C it is called a cold cloud. Inside a warm cloud, small water drops will become large ones through collision and coalescence, and will finally break the buoyancy of the cloud and fall out of its bottom to become rainfall to the ground.
Yes. It is possible and it can increase the precipitation rate upto 10-15%. But it's not considered as a fundamental way since at the first step suitable cloud is needed.
Kousha Hoghoughinia ,thanks a lot. In some cases clouds exist but relative humidity is very low as in interior deserts as in Iraq or lands surrounded by high mountains from all sides as in Iran.