Adapting To Climate Change In Yorkshire–Part II

By Paul Homewood

 

http://www.yourclimate.org/pages/regional-adaptation-study

 

Yesterday I took a look at the “Yorkshire and Humber Regional Adaptation Study” published in 2009, which warned us of all the cataclysmic changes to our climate we could expect to see by 2050.

In Part I, we looked at the prospect of rising temperatures, and saw that their claims were not supported by the trends of the last decade and more.

In Part II, we’ll look at rainfall.

 

 

CLAIM 1 – A reduction in annual rainfall of up to 6%.

Again we use the regional statistics supplied by the Met Office for N & NE England . Figure 1 shows the annual precipitation trends.

 

Figure 1

 

Annual rainfall has increased from the unusually low levels seen in the 1990’s, but the long term trend has now been flat for over a decade, and is at a similar level to first half of the 20thC.

There is certainly no evidence of any decreasing trend, or that current levels of rainfall are in any way unusual.

 

CLAIM 2 – Greater seasonality of rainfall, with increases in winter, combined with significant reductions in summer.

 

Figure 2 & 3 plot winter and summer precipitation.

 

Figure 2

 

Figure 3

 

Far from increasing, winter rainfall has been declining in recent years. Levels in recent years are much lower than many periods in the 20thC, such as the late 1970’s. What is also apparent is that year-on-year variability has been much less in the last 20 years, than it was for most years in the last century.

To that extent, we are experiencing a much more stable climate, that should need less “adaptation” and not more.

As for summer rainfall, the contrast is even starker. Instead of the projected “significant reductions”, we have been experiencing steady increase since the mid 1990’s. Summer rainfall trends are now high by historical standards.

It is worth noting here that “projections” are made from a 1960-90 baseline (see page 14 of the full report here.) Page 25 quantifies the “significant reductions” as about 25% from that baseline, which would imply a level of 140 mm per summer.

Given the current relatively high level of summer rainfall, it is quite likely it could fall back to historical levels, (the average from 1910 – 2000 was 193 mm.) But there is no evidence in the record to support a figure of 140 mm.

 

CLAIM 3 – In northern and upland areas an increase in the number of extreme rainfall events

Unlike the previous claims, there is a nugget of truth in this one. Figure 4 takes the daily rainfall data at Bradford from 1910 – 2012, and plots the top 20 rainfall days.

 

Figure 4

Although the number of extreme rainfall days does not seem to have risen in recent years, the amounts received do seem to have increased. This impression is largely influenced by the heavy rainfall on 14th June 2007. Whether one single event, such as this, has any statistical significance is debatable. It also needs to be borne in mind that the record of 82.8 mm in 1986 stands well above anything since.

 

CLAIM 4 – Dry spells (over 10 consecutive days without rain) are expected to increase in number.

There is no data from the Met Office, which directly addresses the question of consecutive days, but they do offer stats on the number of raindays (when more than 1mm is measured). These numbers are available from 1961.

Figure 5 shows the number of raindays per annum, and, for good measure, Figure 6 looks at raindays during just the summer months, when the Report projected much drier weather.

 

Figure 5

 

Figure 6

 

The annual record shows a few ups and downs over the full record, with no apparent trend. If anything, since 1990, the trend is to more raindays, (and therefore logically fewer dry spells).

During the summer months, there is a clearly defined increase in raindays since the mid 1990’s, and the long term trend is back to that of the early 1960’s. Although rainday data is only available from 1961, the summer rainfall stats in Figure 3 would suggest that the current level is similar to that of the years prior to 1960.

 

Summary

Apart, possibly, for the case of extreme raindays, there is no evidence that current trends over the last decade or more support the claims made in the report. Indeed, in some instances the trends actually go the opposite way to what has been projected.

Of course, none of this means that the trends during the next 30 years will remain the same as those of the last decade. It is well established, for instance, that the cold phase of the AMO, due to start in the 2020’s, will tend to bring drier summers.

But if a business published a budget plan that was so devoid of reality for so long, heads would have been on the chopping block by now.

 

In Part III, we’ll wrap up the other claims. I’ve not yet analysed them, but I don’t hold high hopes that they will any more realistic!

 

References

As with the temperature data in Part I, the data is sourced from the Met Office.

http://www.metoffice.gov.uk/climate/uk/summaries/datasets