Flood Risk Assessment: Flood Warning and Forecasting Flashcards
Why is flood forecasting and warning important?
It enables timely evacuation, infrastructure protection, emergency response, and minimises damage.
Timely warnings allow operational control like opening sluice gates or ______ floodwater to offline storage.
diverting
True/False
Social media is now used to issue flood warnings in the UK.
True
What defines the grade of a flood warning?
The predicted severity and confidence in the forecast.
Minimum lead time required for effective warning is ___ minutes
EA targets ___ hours.
30 minutes
2 hours
What three qualities must flood forecasting models have?
Fast, accurate, and reliable (esp. under pressure).
Forecast models use real-time data from rainfall and ________ or level gauges.
streamflow
What is the difference between flood forecasting and estimation
Forecasting is real-time and operational; estimation is design/planning based on return periods.
Linear regression is most accurate when gauges are far apart.
False (more accurate when close, but then limited lead time)
What is the purpose of converting regression models into matrix form?
To efficiently estimate parameters a and b using all time steps.
What do you input into matrix
R in the example?
Columns of
uk and xk from observed data
Parameter values (a, b) are constant during a flood event.
False – they may vary and need updating
What does a Grade 1 – Flood Alert mean?
Flooding is possible.
Action: Be prepared.
What does a Grade 2 – Flood Warning mean?
Flooding is expected.
Action: Act now.
What does a Grade 3 – Severe Warning mean?
Severe flooding with danger to life.
Action: Act now, evacuate.
What is the role of rainfall data (radar, raingauge) in flood forecasting?
Input data
What is HYRAD used for in flood forecasting?
Rainfall visualisation
What is the role of forecasting/modelling in flood systems?
Predict floods.
What is the role of flood warning systems?
Dissemination and response
IF–THEN Rules
Q: What are IF–THEN rules based on in forecasting?
Operator experience
Linear Regression
What does linear regression do in forecasting?
Simple input–output modelling
Transfer Function
What does a transfer function add in forecasting?
Storage/memory effect
Complex Models
What do complex models represent in forecasting?
Full hydrologic/hydraulic systems.
Simple regression:
x̂ₖ₊₄ = a · uₖ
Where uₖ = upstream flow at time k, and x̂ₖ₊₄ = forecast downstream flow ___ hours later.
4
Formula
x̂ₖ₊₁ =
a · uₖ₋₁ + b · xₖ
This includes system memory (storage)
A 2-hour lead time can be obtained by using:
x̂ₖ₊₂ = a · uₖ + b · x̂ₖ₊₁
Formula
Normal Equation
θ = ___
(RᵀR)⁻¹ Rᵀ X̂
Where:
* R: matrix of predictors
* X̂: observed/target output
* θ: vector of parameters
What is the purpose of state updating?
To correct the state variable x̂ₖ.
What does error updating do?
Adjusts for forecast error trends.
What is parameter updating used for?
Re-estimating model coefficients (a, b).
State Updating
Formula
x̂ₖ₊₁ = ___
a · uₖ₋₁ + b · xₖ
Kalman Filter (Advanced State Updating)
Kalman update equation:
x̂ₖ₊₁ =____
a · uₖ₋₁ + b · [αₖ x̂ₖ + (1 − αₖ) xₖ]
What does αₖ represent in the Kalman filter?
The weighting between predicted and observed values based on confidence.
Error Updating
Formula
x̂ₖ₊₂ = ____
a · uₖ + b · x̂ₖ₊₁ + f(ξ)
- Where ξ is the forecast error, modelled as:
- ξₖ = xₖ − x̂ₖ
Why do we use parameter updating?
Because the runoff process is non-linear and changing, especially during floods.
What is the assumption of a zero order model?
Parameters remain unchanged
What is the assumption of a first order model?
Parameters evolve with time using derivatives
Graphical Flood Forecasting
Formula
x̂ₖ₊ₐ = ____
a · uₖ + b · xₖ₊ₐ₋₁
What is the flood forecast line?
xₖ₊ₐ₋₁ ≥ (F − a · uₖ) / b
What does statistical (radar-based) rainfall forecasting do?
- Extrapolates storms
- Good for 1 hour
What is the role of NWP in rainfall forecasting?
- Simulates physics
- Good for 1–5 days
What does hybrid rainfall forecasting do?
Blends both statistical and NWP using lead time weighting
Radar Forecast
Formula
u = a · Rᵇ
Where:
* u: rainfall rate
* R: radar reflectivity
* a, b: calibrated parameters
What’s the difference between C-band and X-band radar?
- C-band: wide range, high power, immobile
- X-band: lower power, mobile, better resolution
UK NWP now uses ___ km² resolution models and ensemble forecasts (e.g. STEPS).
1 km²
