Djibouti City, intense short-duration rainfall on an arid urban catchment. Flash-flood exposure in informal settlements. You are the DOC duty analyst as the forecast window opens.
Act I quiz — build the evidence inventory Every answer becomes an input to the risk model: evidence → classification → confidence → belief update → decision. Not scored.
Q1. The rainfall outlook for Djibouti City comes from the ECMWF ensemble (many parallel model runs, updated daily). First, the basics: what is a DETERMINISTIC forecast? A single model run giving one outcome — no range of possibilities Many model runs combined into probabilities A forecast that is always correct An observation of what has already happened BN purpose: Forecast literacy — why a single number is not enough for risk decisions.
Q2. And what is an ENSEMBLE prediction system (EPS)? The same model run many times from slightly different starting conditions, giving a spread of outcomes Several forecasters voting on the most likely outcome One model run at a higher resolution An average of past observed seasons BN purpose: Why forecasts are SOFT evidence in the BN — the spread is the confidence.
Q3. What is the strongest evidence currently available? On your desk this round: 7-day antecedent rainfall (IMERG) · Ensemble-mean exceedance prob (ECMWF P_heavy)
Forecast Observation Community report Historical analogue BN purpose: Determines which BN node receives the highest weight.
Q4. Classify that evidence. Check the tags on the evidence cards: 7-day antecedent rainfall (IMERG) · Ensemble-mean exceedance prob (ECMWF P_heavy)
Hard Soft Virtual BN purpose: Determines confidence weighting — hard = observation (one-hot), soft = probability vector, virtual = likelihood message.
Q5. How reliable is this evidence? Djibouti City is a TAIL-risk case — the ensemble mean can look benign while a few members carry the danger; weigh the tail, not the average. Reliability sets how hard the BN leans on it.
Very Low Low Moderate High Very High BN purpose: Evidence likelihood weighting.
Q6. What hazard condition does this evidence support in Djibouti City, Djibouti? Which mechanism fits Djibouti City — slow river rise, sudden flash runoff, or urban-drainage overload? The mechanism decides which impacts follow.
Heavy rainfall River flooding Flash flooding No hazard BN purpose: Updates the hazard node.
Q7. Which impact pathway is most likely here? Djibouti City, intense short-duration rainfall on an arid urban catchment. Flash-flood exposure in informal settlements. You are the DOC duty analyst as the forecast window opens.
Population displacement Road disruption Crop loss Water contamination BN purpose: Updates the impact node.
Q8. What evidence would you request next? Still off the table this round: Ensemble-max / 2-yr RP (pixel p95) · Spatial coverage of heavy-rain pixels · Yesterday's posterior carried forward (DBN, alpha=0.6) · Observed rainfall / river response. Which would most reduce your uncertainty before you decide?
Satellite observations Gauge observations Hydrological model Field assessment Exposure information BN purpose: Real DOC operations seek more evidence — watch which cards the Act II rounds reveal.
Q9. Djibouti City is hyper-arid, averaging only around 150 mm of rain per year, and is crossed by ephemeral wadis such as the Ambouli. Which flood mechanism dominates when heavy rain is forecast? In arid climates a large share of the annual total can arrive in a single storm.
Flash and pluvial flooding: a single intense convective burst can deliver a large fraction of the annual rainfall in hours, overwhelming dry wadis and minimal urban drainage Slow seasonal riverine flooding from a large permanent river rising over weeks Groundwater flooding from a rising water table Snowmelt floods from the Goda mountains BN purpose: Why a tail-risk signal matters in an arid city: the climatological mean is tiny but single-event extremes drive all the impact.
Q10. Which exposure pattern most concerns the duty analyst for Djibouti City as the forecast window opens? Look at where the lowest-income neighbourhoods have been built.
Dense low-income quartiers such as Balbala have grown on and around the Ambouli wadi floodplain, where runoff naturally concentrates The population lives mainly on elevated ridges far from any wadi Exposure is limited to the port's container terminal Buildings are uniformly flood-engineered, so exposure is negligible BN purpose: Exposure context: settlement in the runoff convergence zone means even localized heavy-rain evidence warrants escalation.
Q11. Your current risk estimate — before the model runs? Djibouti City is a TAIL-risk case — the ensemble mean can look benign while a few members carry the danger; weigh the tail, not the average. No model has spoken yet — commit your own read so Act III can compare it to the engine.
Low Moderate High Very High BN purpose: Your pre-BN estimate. Act III compares it against the engine risk indication.
Q12. Recommended DOC status — commit now, before seeing the BN output. The ensemble mean may look benign but the tail signal is rising ahead of onset. What DOC level do you set, and why? A 'Watch + re-check + note the tail uncertainty' is a strong answer.
Monitor Watch Warning Emergency Coordination BN purpose: Your pre-BN decision. Act III compares it against the CRMA state.
Q13. The risk model you are about to work with was built from expert rules, not calibrated against decades of events. How much should you trust it? No right answer — your stance is revisited in Act III against what the model actually did, and what history recorded.
Fully — it computes probabilities Not at all — rules are subjective As a transparent colleague — consistent and inspectable, but encoded judgment BN purpose: Hold this question. Act III returns to it.