Summary of observed changes in precipitation and temperature extremes D9

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Summary of observed changes in precipitation and
temperature extremes (D9)
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Objective

• Are extremes becoming more severe?
• Are they becoming more frequent?
• How is the spatial pattern of the observed
  changes?
• Is there seasonal variability in the changes?

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Method of analysis

• Time series of
• Daily precipitation,
• Daily max/min temperatures
• Definition of indices that correspond to extremes
• Calculation of annual seasonal values of the
  indices
• Linear regression applied on the time series of
  the calculated indices
• Non-parametric test of significance

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Study regions and numbers of stations investigated
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Extreme indices investigated

• Designation Description
• Precipitation related indices
• Prec90p 90th percentile of rainday amounts
  (mm/day)
• 644R5d Greatest 5-day total rainfall
• 646SDII Simple Daily Intensity (rain per rainday)
• 641CDD Max no. of consecutive dry days
• 691R90T of total rainfall from events gt
  long-term 90th percentile
• 692R90N No. of events gt long-term 90th percentile
  of raindays
• Temperature related indices
• Tmax90p Tmax 90th percentile
• Tmin10p Tmin 10th percentile
• 125Fd Number of frost days Tmin lt 0 C
• 144HWDI Heat wave Duration

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Results

• Europe
• Heavy precipitation extremes
• Winter
• Increased in central Europe, the UK and
  Scandinavia.
• Decreased in Eastern Europe, Greece, and western
  Iberian Peninsula.
• Summer
• increased across northern Scandinavia and Russia
• decreased across the UK and NE Europe
• increased through SW Europe
• decreased across the northern Iberian Peninsula.

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• Dry day persistence
• Winter
• increased in the southern part of the region
• decreased in the north
• the increase is generally greater than the
  decrease
• Summer
• Less coherent signal
• Most stations in the central part, the UK, and
  southern Scandinavia
• showed an increase.

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Temperature extremes

• Winter
• Extreme maximum temperature increased over most
  of the region except the SE
• Extreme minimum temperature increased over the
  entire region apart from small decreases in parts
  of Greece, the Iberian Peninsula and Scandinavia
• Extreme minimum temperature increased to a larger
  degree than the corresponding extreme maximum
  temperature
• Summer
• Extreme maximum temperature incresed in most area
  of the region except in northern Scandinavia,
  Eastern Europe, and Russia
• Extreme minimum temperature increaded in most
  areas except that a few stations showed a
  decrease

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Local scale trends in extreme heavy precipitation
indices
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Local scale trends in extreme maximum temperature
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Precipitation trends / Floods

• Areal precipitation vs. Point precipitation
• Simultaneous occurrence of extremes
• Differences between trends corresponding to
  nearby stations
• Trend ? Interpolation or Interpolation? Trend

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Trends in the areal precipitation indices
Point scale
Grid size of 10km x10km
Winter trends in the 5 day total rainfall amount
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Summary

• There are significant trends in the extreme
  indices
• Variability increases
  (Ex. dry day duration and 5 day sums both
  increase)
• Trends in downscaled series

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