Climate change in the Okavango Delta Piotr Wolski, Mike Murray-Hudson Harry Oppenheimer Okavango Research Centre (HOORC) Maun, Botswana Ecohydrological

Climate change in the Okavango Delta

Piotr Wolski, Mike Murray-Hudson

Harry Oppenheimer Okavango Research Centre (HOORC)Maun, Botswana

Ecohydrological processes and sustainable floodplain management, Lodz, 19-23 May 2008

Linking hydrological variability to ecosystem functionality in the Okavango Delta, Botswana, in the

context to adaptation to climate change


Problem statement

• world largest Ramsar wetland, • unspoiled• development pressure - source of livelihood!• planning and (adaptive) management projects in

place• lack of or poor climate change adaptation

strategy!

• tools available to work out hydrological effects of climate change

• limited quantitative data to develop ecological/ecosystem/landscape models

Aim: linking hydrology to ecology, in the context of climate change,

at a level corresponding to available data


Frequency, duration and depth of inundation vary throughout the system

The Okavango Delta


Long-term dynamics of the system


Link between hydrology and ecology

Ecological function of various floodplain ecotopes

• Permanent swamp– anoxic conditions– accumulation of peat, nutrients and C trapping– limited availability of vegetation to herbivores– channels and lagoons support fish

• Seasonally (regularly, occasionally) inundated floodplains– switching anaerobic-aerobic conditions– intensive nutrient recycling– high biomass and primary productivity– availability of plants to grazers during dry winter

• Drylands– rain-fed ecosystem – supports browsers (throughout the year) and grazers (during wet summer)


General approach to assess effects of climate change on OD

Static ecotope model

GCMsCSIRO

Had3CM CGCM2

GFDL

Okavango catchment rainfall-runoff

model

Delta flooding model

Dynamicecotope model

“energy systems”model

P,T

P,T

Q

Q

Inu

nd

atio

n c

har

act

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t ic

s

Assumption: CC will affect ecosystem mostly through change in hydrological conditions


Static hydrology-ecotope model

Floodplainclass

Sub-class

floodfrequency

flood duration(months/year)

Permanentfloodplain

proper PF1 1 12

fringe PF2 1 8-12Regularlyfloodedseasonalfloodplain

RF1 1 4 - 8

RF2 0.5-1Occasionallyfloodedseasonal

OF 0.1-0.5 1-4

High floodsonly

HFO <0.1 <2

Dryland DL 0 0

After SMEC, 1989

Based on long-term average hydroperiod conditions


Static model results (2020-2050, b2)

Baseline


Long-term dynamics of the system


Vegetation communities

Savanna Grassland

Sedgeland

Aquatics


Dynamic ecotope model

Expert system. Current ecotope depends on:• ecotope in previous year• inundation duration in previous 5 years












Results of dynamic model (2020-2050, b2)


Dynamic model based on energy systems concept

Sedgeland/grassland floodplain system diagram


Dynamic model based on energy systems concept

• lumped model

• no aquatic and dryland ecotopes

at this stage

• grasses/sedges compete for

environmental inputs

• competition moderated by

hydroperiod

• output:

– biomass of grasses and sedges

(primary producers)

– biomass of aquatic (fish) and

terrestrial (mammals)

consumers.

Model diagram


Results of dynamic energy systems model (2020-2050, b2)


Conclusions

• The empirical models linking transformation in the ecosystem to hydrological change are indicative only. More rigorous approach is needed.

• However even at this stage they allow for presentation of changes of a complex system in an understandable and meaningful way.

• Results of global climate models are inconsistent in terms of the magnitude and direction of future change in the Okavango Basin: conditions considerably wetter and drier than those observed in the past are simulated by various models. We are currently looking at convergence of results from muli-model ensembles


Thank you

Documents

Climate change in the Okavango Delta Piotr Wolski, Mike Murray-Hudson Harry Oppenheimer Okavango Research Centre (HOORC) Maun, Botswana Ecohydrological