The Delphi technique is a structured communication process designed to build consensus among a group of experts and stakeholders when opinions differ and a quantitative assessment is needed. It uses rounds of anonymous input and feedback, allowing experts to refine their views based on others ' anonymous contributions. This approach is especially useful when stakeholders are in disagreement and objective quantification of risk is required.

PMBOK® Guide Extract:

“The Delphi technique is a way to reach a consensus of experts. Project risk experts participate in this technique anonymously. A facilitator uses a questionnaire to solicit ideas about the important project risks. The responses are summarized and recirculated to the experts for further comment. Consensus may be reached in a few rounds of this process. The Delphi technique helps reduce bias in the data and keeps any one person from having undue influence on the outcome.”

— PMBOK® Guide, 6th Edition, Section 11.2.2.4

ISO 31000 Reference:

“Facilitated workshops and expert elicitation techniques, such as the Delphi method, can help achieve an objective and consensus-based understanding of complex risks.”

— ISO 31000:2018, Section 6.4.2

In this scenario, since the stakeholders are in disagreement and the project involves complex, location-specific disaster recovery requirements, the Delphi technique (Option D) is the officially recommended approach to achieving consensus and quantifying risk.