“Box 1: Drought definitions
Drought can be experienced and hence defined in different ways. There are essentially four types7:
• Meteorological drought: a period of months to years when atmospheric conditions result in low
rainfall. This can be exacerbated by high temperatures and high evaporation, low humidity and
desiccating winds;
• Agricultural drought: short-term dryness in the surface soil layers (root-zone) at a critical time in the
growing season.The start and end may lag that of a meteorological drought, depending on the preceding
soil moisture status;
• Hydrological drought: prolonged moisture deficits that affect surface or subsurface water supply,
thereby reducing streamflow, groundwater, dam and lake levels. This may persist long after a
meteorological drought has ended;
• Socio-economic drought: the effect of elements of the above droughts on supply and demand of
economic goods and human well-being.”

The authors then deal with 3 climate factors, in turn, temperature, rainfall and soil moisture.

A different combination of these three factors, with different durations and weightings, is plausibly required to create a chosen form of drought from the 4 definitions above. However, there is little or no guidance by the authors as to which climate factors are causal to which definition of drought, particularly the last.

A model to help farmers, dam builders and decision makers in general, would require the skill to predict when each of the 3 factors is going to combine in time and intensity to create one of the 4 types of drought. Even then, there might be additional factors, such as changes in the types of crops preferred by water users in different years and their different water needs.

The DECR starting point is to assume that a rise in anthropogenic “greenhouse” gases is going to increase the probability of drought, but the report fails to show how such a rise can be used to predict the concurrence of the 3 nominated factors to produce one or more of the 4 classes of drought.

David’s reviewers rebuke him for not doing precisely what the authors did not do.

Moving to the context of the recent Victorian fires, authorities predicted strong, dry, north winds and a high temperature (which is usually a summer consequence). However, the fires might have been less harmful if heavy rain was falling. There might have been far fewer if there had been no lightning. Therefore, a disaster scenario would also need to predict an absence of rain but some lightning. Whether this is easy or hard in this analogy is not the point. The point is that exceptional events appear to require a number of parameters being exceptional at just the same time with just the right intensity. In the Victoria fires case, all needed to come together in the time frame of a day.

Granted, droughts usually last longer than a bad fire day or even a bad fire season. However, the assumption that a congruence of several events critical to droughts will occur in a nominated time span simply cannot be predicted from a starting assumption that GHGs are heating the earth by a degree or so a century. It is hard enough to hindcast just one of the critical parameters with confidence.

Model graphs with both historical and projected performance shown in the DECR often show actual observations spending an uncomfortable period outside the confidence limits, however calculated, and even displaying opposite trends. Because this is visually apparent without recourse to mathematical analysis, it is telling.

The DECR more fully is:

“An assessment of the impact of climate change
on the nature and frequency of
exceptional climatic events. Drought exceptional circumstances.
K. Hennessya, R. Fawcettb, D. Kironoa, F. Mpelasokaa, D. Jonesb, J. Batholsa,
P. Whettona, M. Stafford Smitha, M. Howdena, C. Mitchella,b and N. Plummerb
(aCSIRO, bBureau of Meteorology)
July 2008

“Box 1: Drought definitions
Drought can be experienced and hence defined in different ways. There are essentially four types7:
• Meteorological drought: a period of months to years when atmospheric conditions result in low
rainfall. This can be exacerbated by high temperatures and high evaporation, low humidity and
desiccating winds;
• Agricultural drought: short-term dryness in the surface soil layers (root-zone) at a critical time in the
growing season.The start and end may lag that of a meteorological drought, depending on the preceding
soil moisture status;
• Hydrological drought: prolonged moisture deficits that affect surface or subsurface water supply,
thereby reducing streamflow, groundwater, dam and lake levels. This may persist long after a
meteorological drought has ended;
• Socio-economic drought: the effect of elements of the above droughts on supply and demand of
economic goods and human well-being.”

The authors then deal with 3 climate factors, in turn, temperature, rainfall and soil moisture.

A different combination of these three factors, with different durations and weightings, is plausibly required to create a chosen form of drought from the 4 definitions above. However, there is little or no guidance by the authors as to which climate factors are causal to which definition of drought, particularly the last.

A model to help farmers, dam builders and decision makers in general, would require the skill to predict when each of the 3 factors is going to combine in time and intensity to create one of the 4 types of drought. Even then, there might be additional factors, such as changes in the types of crops preferred by water users in different years and their different water needs.

The DECR starting point is to assume that a rise in anthropogenic “greenhouse” gases is going to increase the probability of drought, but the report fails to show how such a rise can be used to predict the concurrence of the 3 nominated factors to produce one or more of the 4 classes of drought.

David’s reviewers rebuke him for not doing precisely what the authors did not do.

Moving to the context of the recent Victorian fires, authorities predicted strong, dry, north winds and a high temperature (which is usually a summer consequence). However, the fires might have been less harmful if heavy rain was falling. There might have been far fewer if there had been no lightning. Therefore, a disaster scenario would also need to predict an absence of rain but some lightning. Whether this is easy or hard in this analogy is not the point. The point is that exceptional events appear to require a number of parameters being exceptional at just the same time with just the right intensity. In the Victoria fires case, all needed to come together in the time frame of a day.

Granted, droughts usually last longer than a bad fire day or even a bad fire season. However, the assumption that a congruence of several events critical to droughts will occur in a nominated time span simply cannot be predicted from a starting assumption that GHGs are heating the earth by a degree or so a century. It is hard enough to hindcast just one of the critical parameters with confidence.

Model graphs with both historical and projected performance shown in the DECR often show actual observations spending an uncomfortable period outside the confidence limits, however calculated, and even displaying opposite trends. Because this is visually apparent without recourse to mathematical analysis, it is telling.

The DECR more fully is:

“An assessment of the impact of climate change
on the nature and frequency of
exceptional climatic events. Drought exceptional circumstances.
K. Hennessya, R. Fawcettb, D. Kironoa, F. Mpelasokaa, D. Jonesb, J. Batholsa,
P. Whettona, M. Stafford Smitha, M. Howdena, C. Mitchella,b and N. Plummerb
(aCSIRO, bBureau of Meteorology)
July 2008

So the real question is why did so many people stay in their homes until it was too late? Did they or the authorities miss judge the risks? Do you have to have regular fire drills like at work?

We can except the risk of losing homes, provide the homes are known to be empty. It is not a climate problem, it’s humans not managing the evident risks associated with our land usage.

So the real question is why did so many people stay in their homes until it was too late? Did they or the authorities miss judge the risks? Do you have to have regular fire drills like at work?

We can except the risk of losing homes, provide the homes are known to be empty. It is not a climate problem, it’s humans not managing the evident risks associated with our land usage.