Non-Uniqueness and Uncertainty

Many Pasts, Different Futures

A history match is never unique. Many parameter sets reproduce the same past within the measurement noise, yet they disagree about the future. Picking one and trusting it hides the real uncertainty.

The Forecast Fan

An ensemble of matched models overlaps tightly over the history and fans out in the forecast. The width of that fan is the forecast uncertainty, often summarized as a P10 to P90 range.

Data Narrows It

The cure is data. Every extra month of history down-weights the models that cannot reproduce it, so the surviving ensemble narrows and the forecast band shrinks. Uncertainty falls as the record grows.