This document summarizes a thesis defense that studied the vulnerability of cities to soil moisture and groundwater droughts. It proposed an urban drought categorization framework and estimated drought vulnerability for two Dutch cities. The research estimated vulnerability using indicators of exposure, sensitivity, and coping capacity. It found vulnerability generally followed the spatial pattern of sensitivity and was slightly affected by different drought identification techniques. The research contributed an urban drought framework and estimated city-level vulnerability at a fine spatial resolution but had limitations from a lack of validation. Further research areas included validation of the vulnerability method and studying developing country cities or other urban drought types.

1. 1
Vulnerability of Cities to Soil Moisture &
Groundwater Droughts
Ilias Machairas, October 2020
MSc Thesis Defense

2. Importance
Methodology
Research
Questions Results Conclusion

3. Importance
Methodology
Research
Questions Results Conclusion

4. Impact of Droughts on Cities
Land subsidence
Damage on infrastructure
(Environmental Agency, 2016)
Urban parks
wilting
€ 5.2 billion
by 2050
4

5. Motivation
Protection
of cities
5
Vulnerability
Estimation Limited
Literature

6. Importance
Methodology
Research
Questions Results Conclusion

7. Research Questions
• What is the definition of an urban drought?
• How can an urban drought be quantified? How can the inherent characteristics of
groundwater and soil moisture urban droughts be analyzed?
• How can the vulnerability of cities to soil moisture and groundwater droughts be
determined?
7

8. Importance
Methodology
Research
Questions Results Conclusion

9. Urban Drought Categorization Framework
Affected Water Cycle Parts
• Groundwater
inside city’s
boundaries
Affected Water
Cycle Parts
• Reservoirs/
groundwater
• Soil moisture • Ponds/canals/
wetlands
Urban Drought Categorization Framework (1/2)
Drought Category Groundwater Urban
Drought
Soil Moisture Urban
Drought
Open Water Urban
Drought
Water Supply Urban
Drought
Urban drought is a complex phenomenon
Categorization
Steps
9
Urban Drought
Categorization Framework
• Clarification about the Frameworks
Vulnerability Framework

10. Urban Drought Categorization Framework
Affected Water Cycle Parts
Urban Drought Categorization Framework (2/2)
Urban Drought
Categorization
Framework
In the present
study,
Focus on soil
moisture and GW
urban drought
10
Water Functions
Categorization
Exposure * Sensitivity
Hydrological Variables
Inter-relationships
Main Points

11. Vulnerability Estimation – Groundwater Droughts (1/3)
11
Coping Capacity
Framework suggested by
Fritzsche et al. (2014)
Exposure Sensitivity
Vulnerability

12. Vulnerability Estimation – Groundwater Droughts (1/3)
12
Coping Capacity
Framework suggested by
Fritzsche et al. (2014)
Exposure Sensitivity
Indicators
Indicators
Vulnerability
Weights (AHP)
Normalization
Physical Social
Weights (AHP)
Normalization
Weights (AHP)
Normalization
Indicators

13. Vulnerability Estimation – Groundwater Droughts (2/3)
13
Deficit
Drought Characteristics
Areal Extent
Duration
Frequency
Subsidence
data
• Spatial Analysis
• Monthly Block Minima
• Standardized
Groundwater Index
Exposure
• Fixed threshold
• Variable Threshold
• Moving Window
• Median GWL
Technique
Urban Water
Balance Model

14. Vulnerability Aggregation - Groundwater Droughts (3/3)
14
GWL Vulnerability
Exposure (w: 0.24) Sensitivity (w: 0.76)
Physical (w: 0.67) Social (w: 0.33)
WeightsDrought
Experts
Analytical Hierarchy
Process

15. Vulnerability Aggregation - Groundwater Droughts (3/3)
15
GWL Vulnerability
Exposure (w: 0.24)
• Deficit (w: 0.18) (0.36)
• Duration (w: 0.29) (0.64)
• Subsidence (w: 0.53)
Sensitivity (w: 0.76)
Physical (w: 0.67) Social (w: 0.33)
WeightsDrought
Experts
Analytical Hierarchy
Process

16. Vulnerability Aggregation - Groundwater Droughts (3/3)
16
GWL Vulnerability
Exposure (w: 0.24)
• Deficit (w: 0.18) (0.36)
• Duration (w: 0.29) (0.64)
• Subsidence (w: 0.53)
Sensitivity (w: 0.76)
Physical (w: 0.67) Social (w: 0.33)
• Soils (w: 0.11)
• Land Use (w: 0.20)
• Buildings before 1960 (w: 0.13)
• Historical monuments (w: 0.20)
• Shops (w: 0.07)
• Public Buildings (w: 0.13)
• `Ontwatering’ (w: 0.16)
Households with
lowest income
WeightsDrought
Experts
Analytical Hierarchy
Process

17. Vulnerability Aggregation – Soil Moisture Droughts
17
Soil Moisture Vulnerability
Exposure (w: 0.26) Sensitivity (w: 0.74)

18. Vulnerability Aggregation – Soil Moisture Droughts
18
Soil Moisture Vulnerability
Exposure (w: 0.26) Sensitivity (w: 0.74)
• Deficit (w: 0.39)
• Duration (w: 0.61)

19. Vulnerability Aggregation – Soil Moisture Droughts
19
canal
groundwater
level bulge
canal
Soil Moisture Vulnerability
Exposure (w: 0.26) Sensitivity (w: 0.74)
• Deficit (w: 0.39)
• Duration (w: 0.61)
• Soils (w: 0.35)
• Green Areas (w: 0.24)
• Distance to closest canal (w: 0.19)
• Population Density (w: 0.22)
Physical and Social
ground surface

20. Athens
Study Area
Leiden
• Districts with differences
• Construction year
20
• Data problems

21. Importance
Methodology
Research
Questions Results Conclusion

22. Threshold Method
22
Deficit Duration Pooling

23. Drought Identification (Well L-PB46)
23
20 percentile
40 percentile
30 percentile

24. Vulnerability followed sensitivity’s pattern
24
• Groundwater Droughts
• Soil Moisture Droughts

25. Drought identification techniques affected
vulnerability slightly (1/2)
25
Soil Moisture
Droughts

26. Drought identification techniques affected
vulnerability slightly (2/2)
26
Groundwater
Droughts
*

27. Influence of
Indicators to
Vulnerability
27
Rate of change
in vulnerability
Groundwater
Droughts
𝑉𝑒 − 𝑉𝑎
𝑉𝑎
Rate of
change =
e.g.
Ve = Vulnerability excluding land-use
Va = Vulnerability all indicators included

28. Importance
Methodology
Research
Questions Results Conclusion

29. Conclusions
29
2) Vulnerability followed spatial pattern of sensitivity (high uncertainty)
3) Drought identification
techniques
Vulnerability
1) Fixed and variable threshold complement each other
Slightly
affect

30. Assessment of the Vulnerability Method used
30
Advantages
Intuitive approach
Limitations
Low computational cost
Analysis at two levels
No validation was applied
Repository of damages
is required
Research
droughts damages

31. Recommendations for Further Research
31
• Applying Validation to Vulnerability
• Estimating water supply needed to avoid groundwater and soil
moisture droughts
• Vulnerability of a city from a developing country
• Research about open water urban drought

32. Contribution to current knowledge
32
• Urban Drought Categorization Framework
• Estimating vulnerability of a city at a fine spatial resolution

33. References
PBL Netherlands Environmental Assessment Agency, 2016. Subsiding Soils, Rising Costs. English
Summary and Findings. [online] Available at: https://www.pbl.nl/en/publications/subsiding-soils-
rising-costs [Accessed 12 September 2020].
United Nations (2014). World urbanization prospects: The 2014 revision, highlights. department of
economic and social affairs. Population Division, United Nations, 32.
33

34. Discussion
Questions?
34