When demand for decision exceeds supply of information, there is high perceived uncertainty. Thus, look at environmental uncertainty as dependent on the organization rather than on the environment. It is the organization, not the environment that is uncertain. Certainty exists when the organization has all the information it needs to make a decision. Risk is the lack of certainty.
Risk involves attaching probabilistic likelihood estimates to alternative possible outcomes.
When you lack some of the information you need, you estimate the information and guess at the likelihood that your guess is correct. How to characterize the environment demand structure. It is often useful to distinguish two types of environments. Distinguish the task from the general environment. It affects everybody.