atprm
05-11-2008, 09:43 AM
I heard the other day on the news that they expect this to be the WORST and DEADLIEST tornado season record! Yet, when I went to quote that I couldn't find it.
I did run across the following article, which seems to hold true to what I heard on the news.
~*~
ISSUES IN REPORT DATABASES
The historical records of the occurrence of and losses from severe thunderstorms and tornadoes present significant challenges in attempting to establish trends, if they exist. Very few countries collect data on events as an activity of the national meteorological service. Within those that do, spatial and temporal differences in reporting procedures or effort mean that consistency is rarely achieved (e.g., Doswell et al. 2005). It is likely that the highest-quality dataset of significant length is the tornado dataset of the United States, which began in the early 1950s. Even these data have serious problems with consistency (Brooks 2004; Verbout et al. 2006) (e.g., Fig. 1). Even though the vast majority of the increase has been in the weakest tornadoes (Brooks and Doswell 2001b), serious inhomogeneities exist even when consideration is restricted to the strongest tornadoes, which have
typically been viewed as being better reported (Fig. 2). Recent and planned policy changes within the US National Weather Service may add even more problems to the interpretation of the record.
The number of tornadoes reported per year has increased by about 13 per year, or roughly 1% of the current number of reports. Fundamentally, it is effectively impossible to determine whether any changes have occurred in the actual meteorological events from the official observed records in the US. Relatively large physical changes (say, 20% in the period of record) could have happened, but would be difficult to detect in the background of reporting issues. There is a profound break in the reported number of strong tornadoes (at least F2 on the Fujita scale, going from F0 to F5) in the mid-1970s, as shown in Fig. 2. Brooks (2004) also showed that the reported path length and width information has undergone large changes, seemingly independent of official policy alterations.
It is possible to smooth the report data to produce a distribution of tornado occurrence that may be a reasonable estimate of “truth” (Brooks et al. 2003a), but that smoothing is likely to make the estimate sufficiently resistant so that real changes would be masked. In related work, Dotzek et al. (2003, 2005) and Feuerstein et al. (2005) have shown that the distribution of tornadoes by intensity is similar over much of the world by fitting statistical distributions to reports. Although different environmental regimes can be distinguished (e.g., the US vs. the United Kingdom), the quality of the fit at the most intense end of the spectrum, which represents the rarest events, means that detecting changes in the distribution by intensity of the strongest tornadoes will be difficult at best, unless those distributions are very different.
ENVIRONMENTAL CHANGES
An alternative approach to the question of changes in meteorological events is to look for possible changes in environmental parameters favorable for severe thunderstorms. Brooks et al. (2003b) followed techniques from forecasting research and developed relationships between large-scale environmental conditions and severe thunderstorms and tornadoes, using global reanalysis data. Recently, the work has been expanded to look at a longer
period of record around the globe. Interannual variability on a global scale in the frequency of favorable severe thunderstorm environments has been large, with no discernable trend. Regionally, there have been changes, although
the question of the quality of the reanalysis representation requires caution to be applied to the interpretation. The eastern US showed a decrease from the late 1950s to the early 1970s, followed by a slow increase through the 1990s.
The inflection point in 1973 in the US record is consistent with an inflection point in the number of reports of 3-inch (7.5 cm) diameter and larger hail per year. The reanalysis suggests an increase of 0.8% per year in the number of
favorable environments in the region, whereas the reports have increased by 6%. If we take the reanalysis as an estimate of the real changes, a step to be taken with a grain of salt, it implies that the environmental changes have
accounted for about 13% of the total changes in reports. It is interesting to note, perhaps, that the reanalysis trend in the US qualitatively resembles the US surface temperature record. Observations of events in South America are
insufficient to corroborate the trend seen in the reanalysis.
DAMAGE AMOUNTS
The question of changes in the property damage caused by severe thunderstorms is a separate issue. The difficulties encountered in the report databases seem minor compared to those in the damage databases. Again, the systematic collection of data is a serious issue. Looking at historical descriptions of damage in national meteorological services, it is not always apparent whether damages that are reported are insured losses or total losses. Also, for some storms, no monetary estimate may be given. In other cases, the estimates that get recorded may be preliminary. For example, in
some sources, the 1975 Omaha, Nebraska tornado is listed as the biggest-damage tornado, in inflation-adjusted dollars, in US history, based on a statement made the next day by the mayor of the city that there might be $750 billion in damage, an estimate that turned out to be high by a factor of three. Nevertheless, the original estimate made it into some “official” records and still appears in some lists of the damage.
Another issue is that severe thunderstorm damage tends to be relatively isolated (in space), but occurs relatively frequently. Where and when storms occur can dramatically affect the amount of damage, even for the exact same
meteorological event. An urban area may suffer little property damage from a widespread fall of 1 cm diameter hail, while a vineyard or grain crop at certain times of the year might be devastated. Hail of 5 cm diameter might cause vast
amounts of damage in an urban environment, especially to vehicles, while, if it occurs before crops have emerged from the ground in spring, it might have little impact in a rural location. Brooks and Doswell (2001a) looked at the record of property losses from the most damaging tornadoes in the US from
1890-1999 and adjusted the losses for inflation and national wealth.
They found that, by including the wealth adjustment, there was no tendency for changes in the most damaging tornadoes in recent years, with a return period of about 10 years for a billion dollar tornado. As possible support for the notion of using wealth adjustment, Beatty (2002) took the most damaging tornado from the Brooks and Doswell study, the Saint Louis tornado from 1896 and put its damage path on the current area to estimate property damage. His estimate was about 10% smaller than the approximately $3 billion estimate from Brooks and Doswell based on national wealth adjustment.
http://64.233.167.104/search?q=cache:jcLHf328ilQJ:sciencepolicy.colorado .edu/sparc/research/projects/extreme_events/munich_workshop/brooks.pdf+higher+probability+of+tornadoes+this+ye ar%3F&hl=en&ct=clnk&cd=10&gl=us&client=firefox-a
I did run across the following article, which seems to hold true to what I heard on the news.
~*~
ISSUES IN REPORT DATABASES
The historical records of the occurrence of and losses from severe thunderstorms and tornadoes present significant challenges in attempting to establish trends, if they exist. Very few countries collect data on events as an activity of the national meteorological service. Within those that do, spatial and temporal differences in reporting procedures or effort mean that consistency is rarely achieved (e.g., Doswell et al. 2005). It is likely that the highest-quality dataset of significant length is the tornado dataset of the United States, which began in the early 1950s. Even these data have serious problems with consistency (Brooks 2004; Verbout et al. 2006) (e.g., Fig. 1). Even though the vast majority of the increase has been in the weakest tornadoes (Brooks and Doswell 2001b), serious inhomogeneities exist even when consideration is restricted to the strongest tornadoes, which have
typically been viewed as being better reported (Fig. 2). Recent and planned policy changes within the US National Weather Service may add even more problems to the interpretation of the record.
The number of tornadoes reported per year has increased by about 13 per year, or roughly 1% of the current number of reports. Fundamentally, it is effectively impossible to determine whether any changes have occurred in the actual meteorological events from the official observed records in the US. Relatively large physical changes (say, 20% in the period of record) could have happened, but would be difficult to detect in the background of reporting issues. There is a profound break in the reported number of strong tornadoes (at least F2 on the Fujita scale, going from F0 to F5) in the mid-1970s, as shown in Fig. 2. Brooks (2004) also showed that the reported path length and width information has undergone large changes, seemingly independent of official policy alterations.
It is possible to smooth the report data to produce a distribution of tornado occurrence that may be a reasonable estimate of “truth” (Brooks et al. 2003a), but that smoothing is likely to make the estimate sufficiently resistant so that real changes would be masked. In related work, Dotzek et al. (2003, 2005) and Feuerstein et al. (2005) have shown that the distribution of tornadoes by intensity is similar over much of the world by fitting statistical distributions to reports. Although different environmental regimes can be distinguished (e.g., the US vs. the United Kingdom), the quality of the fit at the most intense end of the spectrum, which represents the rarest events, means that detecting changes in the distribution by intensity of the strongest tornadoes will be difficult at best, unless those distributions are very different.
ENVIRONMENTAL CHANGES
An alternative approach to the question of changes in meteorological events is to look for possible changes in environmental parameters favorable for severe thunderstorms. Brooks et al. (2003b) followed techniques from forecasting research and developed relationships between large-scale environmental conditions and severe thunderstorms and tornadoes, using global reanalysis data. Recently, the work has been expanded to look at a longer
period of record around the globe. Interannual variability on a global scale in the frequency of favorable severe thunderstorm environments has been large, with no discernable trend. Regionally, there have been changes, although
the question of the quality of the reanalysis representation requires caution to be applied to the interpretation. The eastern US showed a decrease from the late 1950s to the early 1970s, followed by a slow increase through the 1990s.
The inflection point in 1973 in the US record is consistent with an inflection point in the number of reports of 3-inch (7.5 cm) diameter and larger hail per year. The reanalysis suggests an increase of 0.8% per year in the number of
favorable environments in the region, whereas the reports have increased by 6%. If we take the reanalysis as an estimate of the real changes, a step to be taken with a grain of salt, it implies that the environmental changes have
accounted for about 13% of the total changes in reports. It is interesting to note, perhaps, that the reanalysis trend in the US qualitatively resembles the US surface temperature record. Observations of events in South America are
insufficient to corroborate the trend seen in the reanalysis.
DAMAGE AMOUNTS
The question of changes in the property damage caused by severe thunderstorms is a separate issue. The difficulties encountered in the report databases seem minor compared to those in the damage databases. Again, the systematic collection of data is a serious issue. Looking at historical descriptions of damage in national meteorological services, it is not always apparent whether damages that are reported are insured losses or total losses. Also, for some storms, no monetary estimate may be given. In other cases, the estimates that get recorded may be preliminary. For example, in
some sources, the 1975 Omaha, Nebraska tornado is listed as the biggest-damage tornado, in inflation-adjusted dollars, in US history, based on a statement made the next day by the mayor of the city that there might be $750 billion in damage, an estimate that turned out to be high by a factor of three. Nevertheless, the original estimate made it into some “official” records and still appears in some lists of the damage.
Another issue is that severe thunderstorm damage tends to be relatively isolated (in space), but occurs relatively frequently. Where and when storms occur can dramatically affect the amount of damage, even for the exact same
meteorological event. An urban area may suffer little property damage from a widespread fall of 1 cm diameter hail, while a vineyard or grain crop at certain times of the year might be devastated. Hail of 5 cm diameter might cause vast
amounts of damage in an urban environment, especially to vehicles, while, if it occurs before crops have emerged from the ground in spring, it might have little impact in a rural location. Brooks and Doswell (2001a) looked at the record of property losses from the most damaging tornadoes in the US from
1890-1999 and adjusted the losses for inflation and national wealth.
They found that, by including the wealth adjustment, there was no tendency for changes in the most damaging tornadoes in recent years, with a return period of about 10 years for a billion dollar tornado. As possible support for the notion of using wealth adjustment, Beatty (2002) took the most damaging tornado from the Brooks and Doswell study, the Saint Louis tornado from 1896 and put its damage path on the current area to estimate property damage. His estimate was about 10% smaller than the approximately $3 billion estimate from Brooks and Doswell based on national wealth adjustment.
http://64.233.167.104/search?q=cache:jcLHf328ilQJ:sciencepolicy.colorado .edu/sparc/research/projects/extreme_events/munich_workshop/brooks.pdf+higher+probability+of+tornadoes+this+ye ar%3F&hl=en&ct=clnk&cd=10&gl=us&client=firefox-a