1. Droughts in Europe Experiences from EU-FP RTD Projects and
Other International Platforms -
Henny A.J. van Lanen

2. Mandate: Drought Impacts
2003 Drought in Europe
River Rhine in 2003 2

3. Mandate: Drought Impacts
Europe: average
15% EU total area affected
17% of EU population
Europe: last 30 years
100 billion Euro
EC (2007) 3

4. Mandate: Drought Occurrence
2011 Drought in Europe
Precipitation anomaly
Jan-March 2011
Soil moisture anomaly
late May 2011
SPI 3 month
early June 2011
JRC
NOAA
UCL 4

5. Climate change – Drought in Europe
Mandate: Drought Impacts
Climate change – Drought in Europe
Major features
annual runoff is projected to decrease in southern and eastern Europe, which likely will lead to more frequent and severe droughts
changes in the seasonal regime particular in cold regions
little is known on groundwater
IPCC (2007); Bates et al. (2007) 5

6. Drought: Urgent Questions
Droughts are large-scale events
and recent severe droughts in Europe pose questions like:
What are the characteristics of extreme historical droughts (onset, severity, persistence, recovery)?
Are there consistent spatial patterns in the occurrence of droughts?
Are we seeing an increase in the scale, frequency and severity of drought?
Are we able to forecast major events?
What about the future (21st century)?
Shows spatial extent - spatial persistence - consecutive regions – local variability
Drought can last for months and years, have large spatial extent, large spatial and temporal variability
What about climate change, e.g. in southern Europe where water already is under pressure
EEA, 2010 6

7. Definitions: Types of Drought
Meteorological Drought
Drought
Propagation
Soil Water Drought
Hydrological Drought
(groundwater & streamflow) 7

8. Definitions: possible confusion
Inconsistent use of terms:
drought
aridity
water scarcity
Norway
Tunesia
India; wells in dry river bed 8

9. Drought and Climate Change
Two main approaches to assess the impact of global (climate and human impacts) change on drought:
analysis of observed data for changes and trends
climate projections using physically based models
The latter requires that the models have been
evaluated for the current climate. 9

10. Observed River Flow Europe European Water Archive:
subset: ~ 400 gauging stations
Europe
Unesco IHP-VII
Drought research:
observation trends
intercomparison large-scale models
Stahl et al. (2010) 10

11. Observed River Flow: Trends
Trend in annual mean flow
dryer
wetter
Trend magnitudes were estimated from the slope of the Kendall-Theil robust line (Theil, 1950).
This slope is also often referred to as the Sen Slope (Sen, 1968).
Growing need, therefore, for observational data with which to discern any emerging trends in river flows, and to compare these with future projections from climate models.
A regional coherent picture in annual streamflow trends with negative trends in southern and eastern Europe and positive elsewhere;
Regime changes:
Clear seasonal patterns in monthly trends with dominating trends towards wetter conditions in winter and towards dryer conditions in summer;
Trends in monthly streamflow elucidated potential causes for these changes.
Stahl et al. (2010) 11

12. Observed River Flow: Trends
Trends in monthly flow ( )
dryer
wetter
Stahl et al. (2010) 12

13. Large-Scale Models: Needed13

14. Large-scale Models Number of Drought: Globe 21st Century
Global Hydrological Model MPI-HM
WFD forcing (CTRL)
3 GCMs forcing for:
(CTRL) A2 A2 B1 B1
Do the models capture hydrological droughts?
Corzo et al. (in prep.) 14

15. Intercomparison Historical Droughts
Large-scale Models:
Intercomparison Historical Droughts
Average drought duration
(scaled):
drought in monthly runoff
10 large-scale models
WATCH Forcing Data
short duration
Following standardization have been applied. For each model:
the number of droughts for all cells have been determined;
percentiles have been calculated from all number of droughts;
finally the number of droughts for each cell has been classified (colour-coded) using the percentiles from the previous line;
Greenland has been excluded.
long duration
Van Huijgevoort et al. (in prep.) 15

16. Intercomparison Historical Droughts
Large-scale Models:
Intercomparison Historical Droughts
low agreement
Average drought duration
Agreement large-scale models (n=10)
Average duration variability between the models for each grid cell given by the
ratio of (P85-P15)/P50, where P is percentile. Low values indicate a high
agreement.
high agreement
Van Huijgevoort et al. (in prep.) 16

17. Trends in Runoff Observations
Trends in annual runoff (observed against 8 models)
Direction and Pattern -> similarities
Magnitude and Variability -> differences
8 models
(dryer)
-100%
+100%
(wetter)
Stahl et al. (submitted) 17

18. Findings
patterns of trends in annual runoff across Europe are well represented by the WATCH set of multi-models
larger differences in simulated monthly trends, esp. in summer
model ensemble mean appears to be closest to the observations
implications for the use of models to estimate patterns of changes in drought
room to improve models (groundwater) 18

19. Dialogue Interfacing required among: Science Policy
Interests (stakeholders)
Management (Water & Land)
Courtesy: Joaquin Andreu
DROUGHT-R&SPI 19

20. Dialogue: Example 5 Science Policy Briefs
5 languages (DE, UK, ES, F, IT)
Characterisation of water bodies and of the analysis of pressures and impacts (WFD, Art. 5);
Monitoring of surface water and groundwater status and of protected areas (WFD, Art. 8)
Recovery of costs for water services (WFD, Art. 9)
Implementing a programme of measures (WFD, Art. 11)
River basin management plans (WFD, Art.13) 20

21. Dialogue: Example Content XEROCHORE Science-Policy Briefs:
policy milestones and key outputs
limitations identified
main recommendations
Examples. 21

22. Dialogue: Example Limitations identified (WFD, Art. 5):
storage capacity (e.g. aquifers, lakes) in a river basin, which reduces drought vulnerability and risk, needs to be better quantified
responsiveness of river basins (i.e. presence of storage) that controls drought propagation (conversion of large-scale meteorological drought into patchy drought in groundwater and surface bodies) needs to be determined
a more consistent modelling approach is required to translate large-scale climate change projections into changes of droughts at river basin scale, incl. uncertainty assessment
WFD characterisation of rivers assumes stationarity, although climate change might alter the nature of the river/aquifer. Non-stationarities need to be considered
Examples. 22

23. Conclusion
EU’s wish to seek an optimal balance between drought response capacity and drought prevention and preparedness (COM(2010) 600 final), which includes reduction of Europe’s risk at drought, will benefit from:
more focus on groundwater in large-scale models
drought forecasting (at least multi-month);
better Science-Policy Interfacing
Examples. 23

24. Further contact: Science-Policy Briefs henny.vanlanen@wur.nl
European Drought Centre:
Science-Policy Briefs
EU-IP WATCH: WATer and global Change:
EU-CSA XEROCHORE: An Exercise to Assess Research Needs and Policy Choices in Areas of Drought:
EU-CP DROUGHT-R&SPI: Fostering European Drought Research and Science-Policy Interfacing 24