Regional differences in meteorological droughts in Great Britain

Transcription

1 Regional differences in meteorological droughts in Great Britain Maliko Tanguy, Klaus Haslinger, Cecilia Svensson, Simon Parry, Lucy Barker, Christel Prudhomme BHS 13 th National Symposium Hydrology: Advances in Theory and Practice University of Westminster Sept 2018

2 Image by Gregor Cresnar, Ralf Schmitzer, Melvin,Alina Oleynik from the Noun Project Outline Motivation and background Methodology Preliminary results Conclusion and next steps

3 Image by Gregor Cresnar, Ralf Schmitzer, Melvin,Alina Oleynik from the Noun Project Outline Motivation and background Methodology Preliminary results Conclusion and next steps

4 Motivation and background Cross-disciplinary understanding of past droughts in the UK Improved tools for managing droughts in future

5 Motivation and background Precipitation Topography Land-use Groundwater Source: Source: Source: from Rivett et al. (2007), However: spatio-temporal characteristics of droughts and differences between these two regions are not well understood

6 Image by Nithinan Tatah from the Noun Project Research questions Do the different regions of GB experience the same frequency of drought events? How different are droughts in the SE and NW? In terms of: area affected duration severity

7 Image by Gregor Cresnar, Ralf Schmitzer, Melvin,Alina Oleynik from the Noun Project Outline Motivation and background Methodology Preliminary results Conclusion and next steps

8 Methodology: clustering Cluster 1 (SE) Cluster 2 Cluster 3 (NW) K-means clustering technique applied in two steps

9 Methodology: identification of drought events Based on Haslinger and Blöschl (2017) s method (Water Resources Research: Moving average of monthly rainfall Gamma distribution fitted Dry areas: threshold = 0.2 quantile Quantile scaled for easier interpretation Contiguous area of dry pixels identified q int = (ξ p) ξ pixel drought intensity q int between 1 (dry) and -4 (wet) q int > 0: dry pixel

10 Methodology: identification of drought events Example: drought (6-months accumulation period) Severity = pixel drought intensity (q int ) x Area x Duration Intensity

11 Methodology: events assigned to region 3-months accum. period 6-months accum. period Drought Core Region (DCR) is defined as grid points of an identified event with a time-average pixel drought intensity (q int )> months accum. period

12 Image by Gregor Cresnar, Ralf Schmitzer, Melvin,Alina Oleynik from the Noun Project Outline Motivation and background Methodology Preliminary results Conclusion and next steps

13 % drought events % drought events Results: Drought events per region NW Transition SE RQ1: Do the different regions of GB experience the same frequency of drought events? 3-months accum. period 12-months accum. period SE Transition NW Top 20 ALL Top 20 Total number of droughts: 373 Total number of droughts: 145 ALL

14 Results: Drought events per region NW Transition RQ1: Do the different regions of GB experience the same frequency of drought events? SE Majority of most severe events in the SE Larger number of less severe events in NW

15 Results: Different droughts per region RQ2: How different are droughts in the SE and NW? In terms of: area affected duration severity Return periods Return period: Inverse of probability (generally expressed in %). E.g.: return period of 100 years probability of occurring is 1/100, or 1% in any one year

16 Return period (years) Return period (years) Mean Area (km 2 ) Results: Return periods (1) 3-months accum. period Mean Area NW Transition Mean Area (km 2 ) 12-months accum. period SE Transition NW SE

17 Return period (years) Return period (years) Duration (months) Results: Return periods (2) 3-months accum. period Duration NW Transition Duration (months) 12-months RR12 accum. period SE Transition NW SE

18 Return period (years) Return period (years) Severity Results: Return periods (3) 3-months accum. RR3 period Severity NW Transition Severity 12-months RR12 accum. period SE Transition NW SE

19 Results: Different droughts per region RQ2: How different are droughts in the SE and NW? In terms of: area affected duration severity Droughts that are: More spatially extended Longer More severe are more frequent in SE than in NW

20 Image by Gregor Cresnar, Ralf Schmitzer, Melvin,Alina Oleynik from the Noun Project Outline Motivation and background Methodology Preliminary results Conclusion and next steps

21 Conclusions (1) 12-months RR12 accum. period Top 20 events Drought events which are: More spatially extended Longer More severe are more frequent in SE than in NW. Number of times each pixel are inside the DCR

22 Conclusions (2) 12-months RR12 accum. period all events However, higher number of small drought events in the NW (short and low intensity events). Number of times each pixel are inside the DCR

23 Next steps Link with hydrology How have droughts evolved over the past 1.5 century? Trend analysis Ranking of drought events

24 Thank you for you attention! BHS 13 th National Symposium Hydrology: Advances in Theory and Practice University of Westminster Sept 2018