HYDROLOGIC PROCESSES, SCALE, CLIMATE VARIABILITY, AND WATER RESOURCES FOR SEMIARID WATERSHED MANAGEMENT
Location: Southwest Watershed Research
Title: Understanding ecohydrological connectivity in savannas: A system dynamics modeling approach
| Miller, G.R. - |
| Cable, J.M. - |
| Mcdonald, A.K. - |
| Bond, B. - |
| Franz, T.E. - |
| Wang, L. - |
| Gou, S. - |
| Tyler, A.P. - |
| Zou, C.B. - |
Submitted to: Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 26, 2011
Publication Date: March 1, 2012
Citation: Miller, G., Cable, J., Mcdonald, A., Bond, B., Franz, T., Wang, L., Gou, S., Tyler, A., Zou, C., Scott, R.L. 2012. Understanding ecohydrological connectivity in savannas: A system dynamics modeling approach. Ecohydrology. 5: 200-220.
Rates of movement and exchange of water depend upon the characteristics and connectivity of pathways in an ecosystem, such as the soil-plant-atmosphere continuum (vertical connectivity), soil properties (both vertical and horizontal connectivity), and the distribution of plants on the landscape (horizontal connectivity). We created a computer model that represents the primary hydrological pathways within an ecosystem with the goal of examining how ecosystem processes are impacted by the connectivity between ecosystem components for savanna sites in the U.S. and Africa. The model successfully reproduced seasonal patterns of soil moisture dynamics and evaporation. It also demonstrated more complex, system-level behaviors, such as interactions that lead to the persistence of drought that depends on the degree of ecosystem connectivity with the atmosphere and groundwater resources. These results highlight the need to further explore mechanisms associated with ecosystem resilience and recovery from changes in water supply.
Ecohydrological connectivity is a system-level property that results from the linkages in the networks of water transport through ecosystems, by which feedback effects and other emergent system behaviors may be generated. We created a systems dynamic model that represents primary ecohydrological networks with the goal of examining how ecosystem processes are impacted by the connectivity between ecosystem components. We focus on savanna ecosystems, although the analyses may be expanded to other ecosystem types in the future. To create the model, a set of differential equations representing ecohydrological processes was programmed into the dynamic solver Vensim. In the model, reservoirs of water storage (e.g., atmospheric and soil moisture) were linked by fluxes of water (e.g., precipitation, evapotranspiration ) that were in turn dynamically controlled by the amount of water stored. Precipitation was forced stochastically, and soil moisture and potential evapotranspiration controlled actual evapotranspiration. The model produced extended, probabilistic time-series of stocks and flows, including precipitation, soil moisture, runoff, transpiration, and groundwater recharge. It was used to describe the behavior of several previously-studied savanna ecosystems in North America and Africa. The model successfully reproduced seasonal patterns of soil moisture dynamics and evapotranspiration at the California site. It also demonstrated more complex, system-level behaviors, such as multi-year persistence of drought and synergistic or antagonistic responses to disconnection of system components. Future improvements to the model will focus on capturing other important aspects of long-term system behavior, such as changes in physiology or phenology, and spatial heterogeneity, such as the patchwork nature of savannas.