ABSTRACT:

Assessing the impact of climate change on floodplain productivity poses unique challenges for hydrodynamic models. For example, the dynamics of floodplain fisheries are governed both by inundation dynamics across thousands of km2, and water storage timing within small depressions (which serve as fish habitat) connected to the river network by meter-scale manmade canals, controlled by flow across fishing weirs. Here, we propose to represent these features as a system of effective, interconnected sub-grid elements within a coarse-scale model. We test this strategy over the Logone floodplain in Cameroon, and its floodplain fishery. We first validate this strategy for a local study area (30 km2); we find that hydraulic models at resolutions from 30 m to 500 m are able to reproduce hydraulic dynamics as documented by in situ water level observations. When applied to the entire floodplain (16,000 km2), we find that the proposed modeling strategy allows accurate prediction of observed pattern of recession in the depressions. Artificially removing floodplain canals in the model causes residence time of water in depressions to be overpredicted by approximately 30 days. This study supports the strategy of modeling fine-scale interconnected features as a system of sub-grid elements in a coarse resolution model for applications such as assessing the sensitivity of floodplain fisheries to future climate change.

Shastry, Apoorva Michael Durand; Jeffrey Neal; Alfonso Fernández; Sui Chian Phang; Brandon Mohr; Hahn Chul Jung; Saïdou Kari; Mark Moritz; Bryan Mark; Sarah Laborde; Asmita Murumkar; Ian Hamilton. 2020. Small-scale anthropogenic changes impact floodplain hydraulics: simulating the effects of fish canals on the Logone Floodplain. Journal of Hydrology, 588: 125035. 125035.10.1016/j.jhydrol.2020.125035.

ABSTRACT:

This interdisciplinary research project focused on the impact of human activities and climate change on African floodplains. African floodplains are an excellent example of coupled human-natural systems because they exhibit strong interactions among multiple social, ecological, and hydrological systems. The intra-annual and inter-annual variations in the area, depth, and duration of seasonal flooding have direct and indirect impacts on ecosystems and human lives and livelihoods. The goal was to develop an integrated computer model that simulates the dynamic couplings among social, ecological and hydrological systems of the Logone floodplain in Cameroon. The model will allow us to simulate the impacts of climate change scenarios and human modifications of the landscape on the social, ecological, and hydrological systems. Fishermen in the Logone floodplain have been modifying the floodplain's hydrology by constructing thousands of individually owned fish canals. The cumulative effect of these canals may equal the impact of large-scale dams.

The devastating impact of large-scale dams on African floodplains has been well documented, but what is less clear is how smaller, slower changes like the fish canals may result in regime shifts that have equally disastrous consequences. If the floodplain is characterized by critical transitions, the gradual increase in fish canals may result in a sudden and catastrophic transition equivalent to the impact of large-scale dams. The integrated computer model will enable researchers to examine the nature of the regime shift. The project brought together a team of researchers from a broad range of disciplines and used a transdisciplinary approach to investigate coupled human and natural systems using a combination of field research, remote sensing analysis, and modeling.

The project will hopefully contribute to the sustainable management of African floodplains, which are of enormous ecological and economic importance, by developing an integrated computer model that will permit stakeholders to evaluate the impact of different human activities and climate change scenarios. The project trained graduate and undergraduate students at the Ohio State University and at Maroua University in Cameroon in quantitative and qualitative, transdisciplinary approaches to the study and management of coupled human and natural systems. This project was supported by the NSF Dynamics of Coupled Natural and Human Systems (CNH) Program and the NSF Office of International Science and Engineering (BCS-1211986).