Food for thought by Ragab, CEH-Wallingford
January 18, 2016
Definition: something that is doubtful or unknown, not really sure. Uncertainty is the situation which involves imperfect and / or unknown information.
The uncertainties in climate predictions arise from our imperfect knowledge of:
- Future rates of human-made emissions and how these will change the atmospheric concentrations of greenhouse gases and the feedback (action & reaction).
- The responses of climate to these changed conditions.
- There are many uncertainties associated with timing, direction and extent of these climatic changes as well as about their implications for societies.
- The response of human beings to climate change is not precisely known and that adds another source of uncertainty.
- Gaps in data and basic understanding of fundamental climatological processes hinder definitive assessments.
- Future unexpected large and rapid changes in climate as those of the past are difficult to predict. These unpredictable surprises arise from the non-linear nature of the climate system.
These uncertainties have great influence on the rational water-resources planning for the future and should not paralyse policy makers and water managers and stop them from rethink and re-evaluate current policies.
Uncertainty in climatic models prediction is improving. Particular uncertainties are associated with clouds and their interaction with radiation and aerosols.
Q: How certain is the future climate change?
A: The only thing that is certain about the future is that the future is uncertain.
Q: Does it make sense to understand the consequences of climate change for water
resources and to begin to plan for those changes?
A: Yes: To see the future is good, to prepare for it is better
Uncertainty in Hydrological modelling results could be attributed to:
- Model assumptions, processes descriptions, mechanisms, mathematical formulation & the numerical scheme.
- In nature all processes operate simultaneously while in model they don’t (they follow order of execution based on flow chart. If evaporation comes after infiltration, expect recharge, soil moisture to be different from the other way around.
- Linearity exists in model processes but not in nature where nothing is linear
- Measurements (e.g. stream flow, soil moisture, Groundwater levels, etc.) and parameters values (hydraulic conductivity, soil physical and plant parameters, etc.) have different values when different measuring devices are used.
- The mismatch between the scale of model application (e.g. 1km2 and the scale of observation, e.g. Point scale).
- Assumptions in climate change predictions and scenarios.
In modelling a complex system: “It is better to be approximately right than precisely wrong”
“No one trusts a model except the man who wrote it; everyone trusts an observation except the man who made it”.
Water Resources management is always associated with the word “sustainability”
- Sustainability is a difficult term to apply especially to groundwater resources as the recharge is difficult to estimate and its forecast over a long period of time is a challenge.
- Sustainability is not for eternity, it should be associated with a time span. The majority of the scientists like the time span to be rather short, with a maximum of 50 years.
“Sustainability is not synonymous with eternity”
Climatic variability is not new
“It is strange what weather we have had all this winter; no cold at all; but the ways are dusty, and the flies fly up and down, and the rosebushes are full of leaves, such a time of the year as was never known in this world before here.”
Samuel Pepys’ Diary 20th January 1661