Savanna Vegetation Changes as Influenced by Climate in East Africa

1. Savanna Vegetation Changes as Influenced by Climate in East Africa Gopal Alagarswamy, Chuan Qin, Jiaguo Qi, Jeff Andresen, Jennifer Olson and Nathan Moore Biocomplexity in the Environment Award 0709671 AAG 2010 Washington DC

2. The EACLIPSE Loop AAG 2010 Washington DC

3. Goal of savanna vegetation modeling • What is physical relation between climate and vegetation? • What shifts in vegetation and changes of grass production are likely to occur in future? • How will vegetation changes influence livelihood systems that depend on livestock and savanna natural resources? AAG 2010 Washington DC

4. Activities • Simulate relation between current climate and savanna vegetation production using ecosystem model Century (Parton et al., 1992) and historical gridded climate data from WorldClim(1950-2000: WorldClim – Hijmans et al., 2005) (18km and 6 km). 2. Validate ecosystem model Century using remotely sensed net primary productivity (NPP). 3. Project vegetation (grass, bush, trees) changes in the future based on projected climate from RAMS. AAG 2010 Washington DC

5. Land Cover of Case Study Sites Mt. Kenya Satellite picture of Mount Kenya

6. Grass Biomass as Simulated by the Century Model in the Northern Site AAG 2010 Washington DC

7. Validating Century Model to simulate biomass (as NPP) • Need measured NPP data over large area to validate Century model. • Field measurements of NPP data over large areas are scarce in the study area. • Can we use remotely sensed NPP data to validate the Century model? AAG 2010 Washington DC

8. Comparison of NPP between Century and MODIS Century NPP MODIS NPP AAG 2010 Washington DC

9. MODIS/ Century NPP Correlation • CENTURY and MODIS NPP are generally correlated with each other. • However, the magnitude of MODIS NPP is much larger than the CENTURY NPP. • WHY?

10. Validation Steps • Compare CENTURY and MODIS grassland NPP of pixels • Using Landcover data: GlobCover 2005. • Problem: Other plant species contribute to NPP. • Calculate grassland-only MODIS NPP • CENTURY Assumption: Whole pixel is covered by grassland. • remotely sensed NPP of a pixel is explained by:

11. Summary of Validation • CENTURY Model can be validated using R.S. data and be used to simulate grass biomass.

12. Relative change in grass biomass from 2000 to 2050 AAG 2010 Washington DC

13. Conclusion • Century does satisfactory job of estimating NPP • Remotely sensed NPP can be used to validate Century Model. • Impact of climate change on NPP varies widely across study area. AAG 2010 Washington DC

14. Next steps • Simulate NPP at higher resolution (6 km) and use additional GCMs. • Simulate NPP of other vegetation types (bush, trees, and crops). • Link vegetation modeling results to field data results to assess the influence of climate on the livelihood systems. AAG 2010 Washington DC

15. Savanna Vegetation Climate Change Local level • Ecosystem structure ( spp ., • Temperature composition, ratio woody/ • Precipitation herbaceous) • Droughts • Forage quant & quality • Floods (palatability) Regional level • Length of growing period • Ecosystem structure • Productivity Temporal & spatial lag effects, non - linear response. Resilience to droughts Livelihood Systems - Non - farm Land Management - Crops Scale: Grazing - Livestock • Intensity • Mobility - Household Income diversification strategies within • Length of Orbit - Community dynamic socio - economic system . Fire Frequency - Regional Household Level decisions on: herd size Land Use and composition, grazing strategy, drought response Landscape Level : fire frequency, land use conversion Figure 1. The savanna human - land - climate system loop. The EACLIPSE Loop

16. Research issues, questions 1. Seasonality shifts: The impact of highly variable and changing rainy seasons on natural vegetation, agriculture, people and livestock. Questions of recovery time of different vegetation types, flexibility of livestock & cropping. • Droughts: How will livelihood systems changes as short-term drought coping strategies evolve to long-term climate change adaptation?

17. Land cover Composition • Those categories contain grassland, but they also have portion of other species. • Thus NPP still includes influence from forest or shrubland. • Since forest or shrubland normally have higher NPP than grassland, the grassland NPP here was overestimated. 1 Rainfed cropland 2 Mosaic cropland(50-70%)/vegetation 3 Mosaic vegetation(50-70%)/cropland 4 Forest 5 Mosaic forest or shrubland(50-70%)/grassland 6 Mosaic grassland(50-70%)/forest or shrubland 7 Closed to open Shrubland 8 Closed to open grassland 9 Sparse vegetation 10 Bare areas 11 Water bodies AAG 2010 Washington DC

18. Grassland-only NPP • CENTURY assume a pixel is covered only by grassland. • While, remotely sensed NPP of a pixel is: • where n is the number of land cover types; • NPPEndmember (i) is the NPP of pure pixel covered by landcover type i. • Our objective is to get NPPEndmember-grassland in each pixel, which is the actual grassland NPP if the whole pixel is grassland. AAG 2010 Washington DC