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

Climate change in the Okavango Delta

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

Climate change in the Okavango Delta

Frequency, duration and depth of inundation vary throughout the system

The Okavango Delta

Climate change in the Okavango Delta

Long-term dynamics of the system

Climate change in the Okavango Delta

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)

Climate change in the Okavango Delta

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

eris

t ic

s

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

Climate change in the Okavango Delta

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

Climate change in the Okavango Delta

Static model results (2020-2050, b2)

Baseline

Climate change in the Okavango Delta

Long-term dynamics of the system

Climate change in the Okavango Delta

Vegetation communities

Savanna Grassland

Sedgeland

Aquatics

Climate change in the Okavango Delta

Dynamic ecotope model

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

Climate change in the Okavango Delta

Dynamic ecotope model

Climate change in the Okavango Delta

Dynamic ecotope model

Climate change in the Okavango Delta

Dynamic ecotope model

Climate change in the Okavango Delta

Dynamic ecotope model

Climate change in the Okavango Delta

Dynamic ecotope model

Climate change in the Okavango Delta

Results of dynamic model (2020-2050, b2)

Climate change in the Okavango Delta

Dynamic model based on energy systems concept

Sedgeland/grassland floodplain system diagram

Climate change in the Okavango Delta

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

Climate change in the Okavango Delta

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

Climate change in the Okavango Delta

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

Climate change in the Okavango Delta

Thank you