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STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 1 Drought : science, tools and trends Takumi Therville University of Antwerp STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 2 Table of contents 1. What is drought? 2. Why study droughts? 3. The different types of droughts 4. Drought monitoring 5. Drought trends 6. Future perspectives STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 3 Table of contents 1. What is drought? STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 4 Definition of drought Droughts refer to periods of time with substantially belowaverage moisture conditions, usually covering large areas, during which limitations in water availability result in negative impacts for various components of natural systems and economic sectors. IPCC 2021 STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 5 What? limitations in water availability STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 6 When? periods of time From a few days and weeks, Through a few months, to several years. STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 7 When/where? below-average moisture conditions STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 8 Drought vs Aridity Drought : temporary abnormally dry Aridity : permanent* climate feature STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 9 Drought vs Aridity Drought Situation 2025-09-01 European drought observatory (EDO) Aridity (Zomer, R.J., Xu, J. & Trabucco, A, 2022) STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 16 Impacts of droughts Social Conflicts, social unrest and breakdown (Lucchetti, 2017) STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 17 Impacts of droughts Social Conflicts, social unrest and breakdown STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 18 Impacts of droughts Economic Transportation and supply chain disruptions Industrial and energetic water restrictions STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 19 What is drought? Drought isn't just a lack of rain — it’s a complex hazard, defined relative to normal conditions, with impacts that ripple through systems. And crucially — no region is immune. STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 20 Table of contents 3. The different types of droughts STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 21 Physical mechanisms STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 22 Physical mechanisms STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 23 Different drought types Meteorological drought •Rainfall deficit •Water vapor deficit STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 24 Different drought types Meteorological drought Agricultural drought •Soil moisture depletion •Vegetation stress •Crop yield reduction Time (duration) STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 25 Different drought types Meteorological drought Agricultural drought Time (duration) Hydrological drought •Reduced streamflow and runoff •Decreased groundwater/reservoir/lake/… levels STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 32 Why do we need drought indices? STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 33 Drought Indices Multi -scale Works at different temporal scales Comparable Provides comparable values across climate regions Interpretable Easy to relate to observed impacts (thresholds, severity) Accessible Can be calculated from available data Sensitive Reacts clearly to water deficits STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 34 The Standardized Precipitation Index (SPI) (McKee et al., 1993) Transform into Standard normal Obtain probability of precipitation amount over chosen period Raw precipitation data Accumulate precipitations over a chosen period STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 35 SPI : Standardized Precipitation Index Multi -scale Works at different temporal scales Comparable Provides comparable values across climate regions Interpretable Easy to relate to observed impacts (thresholds, severity) Accessible Can be calculated from available data Sensitive Reacts clearly to water deficits STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 36 SPI drought definition (Keyantash & National Center for Atmospheric Research Staff (Eds)., 2025) STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 37 SPI : Standardized Precipitation Index Multi -scale Works at different temporal scales Comparable Provides comparable values across climate regions Interpretable Easy to relate to observed impacts (thresholds, severity) Accessible Can be calculated from available data Sensitive Reacts clearly to water deficits STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 38 Drought detection with run theory Duration Severity = Area Intensity = 𝐒𝐞𝐯𝐞𝐫𝐢𝐭𝐲 𝐃𝐮𝐫𝐚𝐭𝐢𝐨𝐧 Peak STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 39 SPI : Standardized Precipitation Index Multi -scale Works at different temporal scales Comparable Provides comparable values across climate regions Interpretable Easy to relate to observed impacts (thresholds, severity) Accessible Can be calculated from available data Sensitive Reacts clearly to water deficits STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 40 SPEI (Vicente-Serrano et al., 2010) •Apply standardization process to 𝐷 = 𝑝𝑟𝑒𝑐𝑖𝑝 − 𝑃𝐸𝑇 where PET is the potential evapotranspiration •Considers temperature’s effect on the water cycle STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 41 Agricultural drought SSI (Sheffield, J. & Wood, E.F., 2008) •Apply standardization process to soil moisture ▪At a certain depth ▪In the total soil column •Different plants use different soil moisture depths •Data scarcity and model assumption dependent STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 48 Online drought monitoring tools and resources https://app.climateengine.org/climateEngine STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 49 Online drought monitoring tools and resources https://www.drought.gov/documents/handbook-drought-indicators-and-indices STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 50 Online drought monitoring tools and resources https://www.drought.gov/documents/handbook-drought-indicators-and-indices STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 51 Table of contents 5. Drought trends a) Historical trends b) Future trends c) Future risk trends STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 52 Trends of drought - historical 52 Figure 11.17 in IPCC, 2021: Chapter 11. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 53 Trends of drought – future climate 53 1.5° 2° 3° We can also look at drought event characteristics… like duration Figure 2-4 a) from Tabari & Willem (2022) STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 54 Trends of drought – future climate 54 1.5° 2° 3° We can also look at drought event characteristics… like duration or frequency Figure 2-4 b) from Tabari & Willem (2022) STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 55 Impacts and risk (IPCC AR5) Impacts Hazard Vulnerability Risk Exposure STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 56 Trends of drought – future risk 56 Figure 4 in Tabari, H. & Willems, P., 2023 : Sustainable development substantially reduces the risk of future drought impacts STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 57 Trends of drought – future risk 57 Figure 4 in Tabari, H. & Willems, P., 2023 : Sustainable development substantially reduces the risk of future drought impacts STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 64 References •IPCC. 2021. Seneviratne, S.I., X. Zhang, M. Adnan, W. Badi, C. Dereczynski, A. Di Luca, S. Ghosh, I. Iskandar, J. Kossin, S. Lewis, F. Otto, I. Pinto, M. Satoh, S.M. Vicente-Serrano, M. Wehner, and B. Zhou, 2021: Weather and Climate Extreme Events in a Changing Climate. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change[Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1513–1766, doi: 10.1017/9781009157896.013. •FAO 2021. The impact of disasters and crises on agriculture and food security: 2021. Rome. https://doi.org/10.4060/cb3673en •UNDRR 2021. United Nations Office for Disaster Risk Reduction (2021). GAR Special Report on Drought 2021: Summary for Policymakers. Geneva. •WMO 2019. WMO Atlas of Mortality and Economic Losses from Weather, Climate and Water Extremes (1970–2019). Geneva. https://library.wmo.int/idurl/4/57564 •World Bank 2017. Damania, Richard; Desbureaux, Sébastien; Hyland, Marie; Islam, Asif; Moore, Scott; Rodella, Aude-Sophie; Russ, Jason; Zaveri, Esha. 2017. Uncharted Waters: The New Economics of Water Scarcity and Variability. © World Bank. http://hdl.handle.net/10986/28096 •IDMC 2022. Internal Displacement Monitoring Centre (2022). Global Report on Internal Displacement 2022. Geneva. •Littell, J. S., Peterson, D. L., Riley, K. L., Liu, Y., & Luce, C. H. (2016). A review of the relationships between drought and forest fire in the United States. Global change biology,22(7), 2353–2369. https://doi.org/10.1111/gcb.13275 •JRC 2023. The EU 2022 wildfire season was the second worst on record. (2023, May 2). The Joint Research Centre: EU Science Hub. https://joint-research-centre.ec.europa.eu/jrc-news-and-updates/eu2022-wildfire-season-was-second-worst-record-2023-05-02_en •Stocker, B.D., Zscheischler, J., Keenan, T.F. et al. Drought impacts on terrestrial primary production underestimated by satellite monitoring. Nat. Geosci. 12, 264–270 (2019). https://doi.org/10.1038/s41561019-0318-6 •Cappucci, A. (2022, August 11) Extreme drought is gripping Europe, intensifying heat and fueling fires. The Washington Post. https://www.washingtonpost.com/climate-environment/2022/08/11/europedrought-heatwave-fires-climate/ •Powers, J. S., Vargas G, G., Brodribb, T. J., Schwartz, N. B., Pérez-Aviles, D., Smith-Martin, C. M., Becknell, J. M., Aureli, F., Blanco, R., Calderón-Morales, E., Calvo-Alvarado, J. C., Calvo-Obando, A. J., Chavarría, M. M., Carvajal-Vanegas, D., Jiménez-Rodríguez, C. D., Murillo Chacon, E., Schaffner, C. M., Werden, L. K., Xu, X., & Medvigy, D. (2020). A catastrophic tropical drought kills hydraulically vulnerable tree species. Global change biology,26(5), 3122–3133. https://doi.org/10.1111/gcb.15037 STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 65 References (cont.) •Delacroix, G. (2022, August 15). Western Europe’s wildlife is suffering from the drought. Le Monde.fr. https://www.lemonde.fr/en/environment/article/2022/08/15/westerneurope-s-wildlife-is-suffering-from-the-drought_5993670_114.html •Von der Brelie, G. (2022, October 20). Climate crisis: how beetles and fire are devouring European forests. Euro News. https://www.euronews.com/2022/10/20/climatecrisis-how-beetles-and-fire-are-devouring-european-forests •Sanders, S. K. D., Van Kleunen, M., Allan, E., & Thakur, M. P. (2024). Effects of extreme drought on the invasion dynamics of by non-native plants. Trends in Plant Science, 30(3), 291–300. https://doi.org/10.1016/j.tplants.2024.10.009 •Al-Aisaee, M. M., Velazhahan, R., Nawaz, A., & Farooq, M. (2025). Morphological, Physiological, and Biochemical Impacts of Drought on Wheat-Pest-Pathogen Interactions. Physiologia plantarum,177(4), e70364. https://doi.org/10.1111/ppl.70364 •Lucchetti, J. (2017, September 15). Drought — a cause of riots. University of Geneva – Press release. https://www.unige.ch/medias/en/2017/la-secheresse-sourcedemeutes •National Geographic. (2018, March 12). How Cape Town’s Residents Are Surviving the Water Crisis—For Now | National Geographic [Video]. YouTube. https://www.youtube.com/watch?v=XxZAqswJfL4 •Alexandru, D. (2023, October 31). Drought monitoring in Romania [slides]. Meteo Romania. https://www.iawd.at/files/File/events/2023/Drought_Conference/DANIEL_ALEXANDRU.pdf •Horowitz, J. (2022, August 18). Europe’s Scorching Summer Puts Unexpected Strain on Energy Supply. The New York Times. https://www.nytimes.com/2022/08/18/world/europe/drought-heat-energy.html •Bevacqua, E., Rakovec, O., Schumacher, D.L. et al. Direct and lagged climate change effects intensified the 2022 European drought. Nat. Geosci. 17, 1100–1107 (2024). https://doi.org/10.1038/s41561-024-01559-2 STRENGTHENING THE RESEARCH CAPACITIES FOR EXTREME WEATHER EVENTS IN ROMANIA Grant Agreement 101159497 66 References (cont. & end) •United Nations, The United Nations World Water Development Report 2023: Partnerships and Cooperation for Water. UNESCO, Paris •UNISDR, 2009. Drought Risk Reduction Framework and Practices: Contributing to the Implementation of the Hyogo Framework for Action. United Nations secretariat of the International Strategy for Disaster Reduction (UNISDR), Geneva, Switzerland, 213 pp •Dumitrescu, A., Micu, D., Guijarro, J. et al. Long-term homogenized air temperature and precipitation datasets in Romania, 1901–2023. 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Lett., 35, L02405, doi:10.1029/2007GL032487. •Bloomfield, J. P. and Marchant, B. P.: Analysis of groundwater drought building on the standardised precipitation index approach, Hydrol. Earth Syst. Sci., 17, 4769–4787, https://doi.org/10.5194/hess-17-4769-2013, 2013. •Tabari, H., & Willems, P. (2022). Trivariate Analysis of Changes in Drought Characteristics in the CMIP6 Multimodel Ensemble at Global Warming Levels of 1.5°, 2°, and 3°C. Journal of Climate, 35(18), 5823-5837. https://doi.org/10.1175/JCLI-D-21-0993.1 •Tabari, H., Willems, P. Sustainable development substantially reduces the risk of future drought impacts. Commun Earth Environ 4, 180 (2023). https://doi.org/10.1038/s43247-023-00840-3