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Overview

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  1. Detection and Statistical Analysis of Severe Drought Events Using Standardized Precipitation Index and Reconnaissance Drought Index,Case Study: Central Aegean Sea, GreeceAnastasiadis Stavros*, Demetris F. Lekkas, Konstantinos MammasAnalysis and Simulation of Environmental Systems Research GroupDepartment of Statistics – Actuarial and Financial Mathematics,University of Aegean

  2. Overview • Regional Drought Assessment • Why is needed? • Method - Drought indices • SPI & RDI • Central Aegean – Data Collections • Results • Conclusions

  3. Drought • Complex – slow developing phenomenon • Spatial and Temporal characteristics • European Drought Center defines “drought means a sustained and regionally extensive occurrence of below average natural water availability” • Last 30 years in Europe • Drought events : 1976 - 1989 – 1991 – 2003 • Since 1991: Average annual economic cost 5.3 € billion • 2003 drought : 8.7€ billion (associated with heat wave) (European Communities,2007) • Meteorological Drought • Many definitions • Regional Characteristics • Usually combination : Degree of dryness and Duration of dry period • A viable meteorological drought definition depends on the study-research purposes

  4. Method • Selection of Drought Index • SPI (Precipitation, Gamma distribution) • (2010) WMO selection as key drought indicator • RDI (Precipitation/PET, lognormal) • (2004) MEDROPLAN • Thornwaite method – Based on temperature • Goodness of fit: Anderson Darling test • Fitting data with MLE estimator • Drought Characteristics • Duration (Length of dry period – indicator below threshold) • Severity (Sum of the negative deviations for a specific drought event) • Intensity (Severity / Duration )

  5. Case Study • Stations • Larisa • Milos • Mytilini • Naxos • Hellenic National Meteorological Service • Time Period : 1955-2010 • Time Step : daily aggregated to Annual • Variables : • Precipitation • Temperature

  6. Precipitation

  7. Temperature

  8. Goodness of fit

  9. Intensity 0.95 (Spi) 0.97 (Rdi) 2000-2010 Intensity 1.13 (Spi) 1.14 (Rdi) 2 2 7 7 1989 2010 1999 (Rdi) 2006

  10. 2000-2010 Intensity 0.93 (Spi) 0.88 (Rdi) Intensity 0.49 (Spi) 0.28 (Rdi) 4 (RDI) Intensity 1.28 (Spi) 1.38 (Rdi) 2 4 3 5 2004 2006 2007 2008 1964 1970

  11. Summary Performance

  12. Common Consecutive Dry Periods in all Stations

  13. Summaring Results Extreme Drought Years • 1989 & 2006 • Related Probability 4.4 % Three Common Periods, with similar or different characteristics (severity) • 1959-1960 • 1989-1990 • 2004-2005 Increases in the duration of Dry Periods and Extreme Events • Since 1985

  14. Fitting distributions ? Is it really necessary for drought assessment ? Identification of the same Extreme Events Identification of the same drought events • Four drought indices : • Spi • Rdi • Unesco Aridity (Standardized) • (NO distribution involved) • Rainfall / Temperature (Standardized) • (NO distribution involved) 2010 Dry conditions companied with Heat Wave 1999 Extreme Event identified only by RDI

  15. Conclusions • Spi world wide applications/ recognition • Temperature should always be included • Impacts are usually more severe when droughts and heat waves are happening at the same time • Question • Does SPI (or of any index) value (e.g. -2) indicate severe drought? Shouldn’t be related to impacts? • Definitions must incorporate both physical and social measures

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