Week 5 – Rainfall Gens
For more information on what are timeseries models and how a weather generator is built – refer to Time Series Models and Time Series Models for Continuous Simulation – strongly recommend to understand the theory behind a weather generator
In the course we are going to focus on the practical aspect of running a weather generator
What is a rainfall generator?
With these statistics a rainfall generator will replicate this rainfall timeseries
Synthetic rainfall timeseries
You have a rainfall series – this series will have a lot of stats:
Rainfall Generator
Rainfall generators vs hydrological models
Trying to tweak the model and re-calibrating it would be a very long exercise on its own
Rainfall generator validation
As in a hydrological model, you can also validate your rainfall generator!
Why do we need a rainfall generator?
Scotland - SEPA
Ile de France - France
England - EA
Ministerio para la Transición Ecológica y el Reto Demográfico - Spain
It doesn’t matter where you are, if you are a hydrologist you will be working with very long return periods!
Why do we need a rainfall generator?
30 year rainfall dataset
Unsuitable for calculation of very long return periods
Rainfall Generator
Generate a 10000 year rainfall dataset
Calculate with more confidence a very long return period rainfall/flood
Return periods - Issues with fitting short timeseries
Bad fitting – Not enough extreme values in a timeseries
These examples are from fitting a 25 year timeseries
Large gaps in the fit
Even when the fitting is appropriate, how to guarantee that extrapolation is good?
Alternative solution -Pooling Groups�
1. Find catchments that have similar characteristics to the one you are studying
2. With all the additional data derive a curve/formula to extrapolate the flow from the studied catchment
3. Use this formula on a 2yr return period event to derive a 100 or 200 year event.
Tasks for the week/next week