Below image was posted on Twitter yesterday by Environment’s Agency David Troup. I like it a lot. To me, it gives an instant overview of flow levels across England and Wales. I’d love to have a similar graphic available in the two forecasting systems I use (the Dutch system for Rhine and Meuse, and EFAS, the European Flood Awareness System).
Some thoughts on below picture:
- I wonder who the target audience for this graphic is. The percentiles are maybe a bit complicated for those not used to it.
- The colours used are different from what I would use. For my application (flood forecasting), I’d express flooding as red, not black.
- More and more often, I see observations and forecasts of hydrological variables expressed as relative values to some reference, rather than in absolute values. Here, the baseline is the climatology of flow at the hydrological stations. In the US, forecasts are often expressed relative to “normal”. This development, I think, comes from Anglo-Saxon environments.
- This overview is well suited if there are not too many stations on the map.
- The map does not indicate whether these flow levels cause flooding or not. At different locations, flooding may occur at
- If similar graphs were to be used for forecasting, one will quickly run out of available dimensions. Forecasts would require the leadtime dimension to be indicated somehow, and also the uncertainty in the forecast. Edwin Welles -a colleague of mine at Deltares- and I have developed some ideas about this, which I’ll share later.
Again, I think Dave’s map is a great way of showing spatially variable information. Above items should be seen as considerations in case similar graphs were to be implemented in the systems I use.
November 12 update: Dave let me know that these maps are used to show water resources situation. Makes perfect sense!