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Piotr Wolski

Piotr Wolski. Climatic and hydrological changes in the Okavango Delta. The Okavango. Mohembo. Maun. The Okavango. it is Delta, not delta it is the 5th largest Ramsar site in the world it is the 3rd largest inland “delta” in Africa. The Okavango. Regional tectonic setting

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Piotr Wolski

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  1. Piotr Wolski Climatic and hydrological changes in the Okavango Delta

  2. The Okavango Mohembo Maun

  3. The Okavango • it is Delta, not delta • it is the 5th largest Ramsar site in the world • it is the 3rd largest inland “delta” in Africa

  4. The Okavango Regional tectonic setting (after Kampunzu, 1998) Frequency of tectonic events (after McCarthy, 1993)

  5. The Okavango • Depth of the Kalahari form aeromagnetic survey (after Brunner, 2007)

  6. Seasonal flood pulse February August

  7. Seasonal flood pulse

  8. Human factor

  9. Exogenous variability? change? Interannual and multidecadal variability. Or is it change? Mohembo Maun

  10. Endogenous change • Channel aggradation and abandonment • Animal action (hippo paths) • Water flow-vegetation-fire feedbacks • Tectonic activity After McCarthy et al.

  11. Multidecadal variability Rainfall CRU dataset and observations Air temperature

  12. Is it rainfall or temperature that affects the Okavango? Multi-Taper Method (MTM) of spectral analysis Observed Both Neither Only P Only T Discharges respond stronger to multidecadal variability in rainfall than in temperature! Wolski et al. submitted

  13. What causes MDV in rainfall? Pacific Decadal Oscillation ???

  14. How will future look like? • 18 CMIP3 GCMs • 42 runs for 20th and 21st century 20th century rainfall: • Multidecadal variability present • Timing is off! 21st century rainfall: • Similar magnitude of MDV to this observed in 20st century • No consistent trend

  15. How will future look like? Multidecadal variability present, but superimposed on downward trend Simulations of Okavango River discharges based on ensemble of GCM runs

  16. Is climate change happening already?

  17. Climate change attribution • Adjustment of: • Atmospheric greenhouse gas concentrations • Sea surface temperatures • Plans to include: • Tropospheric sulphate aerosols • Stratospheric volcanic sulphate aerosols • Sea ice coverage Stone, Lennard, Tadross, Allen, Stott & Pall (2011)

  18. Attribution - results rainfall temperature

  19. Attribution - results Okavango discharge at Mohembo Probability of high floods decreases in warmer climate FAR: -0.03 for 2009 -0.19 for 2010

  20. Skill of models How good is the GCM-hydro model combination in simulating Okavango flows? “Bad” years “Good” years

  21. Self Organizing Maps Classes of synoptic variables in a 6x4 SOM based on NCEP reanalysis data Air temperature @ 2 m Relative Humidity @ 850 mbar

  22. Self Organizing Maps Frequency of synoptic states for each year Significance of difference in frequency between “good” and “bad” years p-value 1 0 There is potential for distinguishing “good” years from “bad” ones based on synoptic conditions

  23. Data deficiency and flood modelling Simulations of Okavango flows based on TRMM rainfall “Tweaked” MIRA + obs TRMM data observed TRMM-based Particularly significant in the context of seasonal forecasting

  24. Endogenous change Sat image Inundation map Time series Distributary inundation

  25. Analysis of change in inundation Pixel inundation status as a function of system’s inundation area Deviation of probability as a function of time

  26. Inundation trends independent on inputs Temporal trend in deviation of probabilities of inundation status Causes not fully understood, yet have implications on planning, management, cc adaptation etc. drier No change wetter

  27. Summary • Okavango – a complex hydrological system, dynamics of which is influenced by several endogenous and exogenous factors: • Interannual climate variability • Multidecadal climate variability • Climate change • Endogeneous system transformation • Tectonics • Geomorphological development of the wetland • Strong international and local appeal – thus need for forecasting at seasonal, decadal and climate-change time-scales

  28. Summary • In the context of expansion of AfricaArray into hydrology/climate research: • understanding of hydrological role of isostatic adjustment in the Delta, both on seasonal and long-term time-scales • understanding of role of tectonic events on distribution of water in the Delta and monitoring of tectonic displacement during events • Verification/improvement of hydrological models using GRACE, in the context of poor rainfall data • Tectonic studies of incipient rifting etc…

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