The aim of this ITT is to develop an event-linked counterfactual evidence layer to support the C3S Operational Attribution Office. Using ECMWF forecasts and reanalysis products, it will derive event-specific counterfactual diagnostics that provide additional evidence on how the intensity, probability or other characteristics of observed extreme events may have differed in the absence of human-induced climate change. ECMWF intends to award a single Framework Agreement, with a maximum duration of 18 months, which shall be implemented via a single multi-annual Service Contract, expected to commence at the beginning of Q1 2027.

C3S2_610 Development of an event-linked counterfactual diagnostic evidence layer based on ECMWF forecast and reanalysis information in support of the C3S Operational Attribution Office

This ITT aims to develop a methodological framework and supporting procedures for generating event-conditioned diagnostic evidence for high-impact extreme events by assessing how key characteristics of observed present-day events would differ under counterfactual climate conditions without anthropogenic warming. Tenderers must propose a scientifically robust and operationally feasible approach, including an assessment of data availability, computational requirements, reproducibility, interpretability and delivery timelines, while confirming that no new large-scale climate or weather model simulations will be undertaken. The successful tenderer will, in consultation with C3S, establish quality requirements and an evaluation methodology to assess the physical consistency, robustness, reproducibility, transparency and limitations of the derived evidence, and will provide a comprehensive handover package to support future operational or pre-operational implementation.