Spatial extent and predictability of various hazards.

Question

My question concerns the following three hazards: earthquakes, hurricanes and drought.

In terms of spatial extent (wide spread, limited), I believe that earthquakes generally have the most limited spatial extent of the three, followed by hurricanes. However, I am unsure about droughts. I assume that they have the largest spatial extent of the three, but would anyone be able to give an explanation as to why?

With regard to their predictability (hazard assessment), I would say that the order (from most predictable to least) would be:

1. Hurricanes
2. Drought
3. Earthquakes

Hurricanes as past trends can be assessed and there are specific conditions that are required for a hurricane to form (e.g. between 5, 20 degrees from equator).

I am less sure about prediction methods for droughts, but I assume that precipitation levels can be monitored, etc.

Lastly, I am aware that historic trends can be assessed for earthquakes and the general areas that will be affected can be predicted, however it is difficult to predict where the earthquake will occur along the fault line and the magnitude (I am aware that there are numerous questions on the predictability of earthquakes)

I would love it if you could share your thoughts in terms of how you would order the hazards and why.

Answer 1

Drought is not comparable to earthquakes and hurricanes because of the difference in time scale involved. We can generally consider earthquakes and hurricanes to be discrete events at a point in time. Drought, however, has a significant and variable time component. For example, you might consider a year of severely below average rainfall to be a drought but there are also multi-year droughts with prolonged periods of low rainfall. Descriptively, you can plot the average rainfall for an area along with the cumulative deviation from the average to see the trends. Even that should be used with caution - one year of very high rainfall may have a big effect on the deviation from the mean but won't really help rain-fed agriculture in subsequent low years. Here is a guide to the different definitions of drought.

The probability of a hurricane hitting the eastern United States in the next decade probably approaches 1.0 but to narrow that down to specific cities is more difficult. Once one has formed, the meteorologists are getting very good at predicting where it will make landfall. In between, the probability of a hurricane striking a particular city in a given year is low.

With regards to earthquakes, there are many known faults where measurements indicate a high probability for a large earthquake. However, the timing may be within hundreds or thousands of years. We can predict where but not when.

These are all different ways of looking at prediction that illustrate the considerations in how we think about 'prediction'. Ranking them is comparing apples to oranges.

Answer 2

One can't order these hazards without being much more precise. What energy threshold do you regard as an earthquake? There is micro-sismicity over most of ther planet for most of the time. The area affected deceases as the magnitude gets larger. And what do you regard as the spatial extent? The slippage footprint, or the area suffering some event magnitude? (difficult to define).

Likewise drought can be defined many different ways. Days without any rain? Days above a particular rain threshold? Days in which evapotranspiration exceeds precipitation? Days above a particular crop wilting point? Do you bring temperature into the equation? Moreover, in these days of climate change, falling water tables,and increasing frequency / intensity of El Nino, the area potentially affected by drought is evolving, so we need to be clear about the time period in our definition.

The area potentially affected by hurricanes varies on each continent, and requires global climatic modelling to define. The oceanic area in which hurricanes can develop has been discussed previously in the Earth Science stack exchange, but the single most important factor is the area with a sea surface temperature of >27 deg C. This is also a variable in these times of climate change.