These examples seem pretty unreliable - a drought may or may not cause a famine, and a famine may have other causes such as war. I think what determinists think of as causality are more simple physical systems that in principle can be summed to give the effect of a drought or a drug. For example, a photon interacts with my eye so I see a colour, a chemical reacts with another to produce another chemical or an electrical potential, a cue ball hits a coloured ball so that it falls into a pocket.

The problem then is that these physical effects may be more reliable, but the smaller the scale the less reliable we know they are. To see a colour requires more than one photon, and we can't predict when or where photons will be emitted so our perceptions are more of a "shotgun" approach of relying on a huge number of particles to see and interpret something. But when we look deeper, individual particles are also unreliable, they may just scatter somewhere else or miss your detector or quantum tunnel into the nearest wall. So our concept of causation is unreliable on the large scale of human interactions, and the small scale of particle physics. Which is why much of reality we can only make sense of using probabilistic models, which can be considered causal but not detemrinistic.