Modelling Impacts of Environmental Water on Vegetation of a Semi-Arid Floodplain-Lakes System Using 30-Year Landsat Data

River floodplains are among the most dynamic and diverse ecosystems on the planet. They are at risk of degradation due to river regulation and climate change. Environmental water has been delivered to floodplains to maintain environmental health by mimicking natural floods. It is important to understand the long-term effects of environmental water to floodplain vegetation to support its management. This study used Normalized Differences Vegetation index (NDVI) from the 30-year Landsat datasets of the Hattah Lakes floodplain in Australia to investigate the drivers of vegetation dynamics. We developed generalized additive mixed models (GAMM) to model responses of vegetation to environmental water, natural floods, precipitation, temperature, and distance to water across multiple spatial and temporal scales. We found the effect of environmental water on floodplain vegetation to be quite different from that of natural floods in both space and time. Vegetation in most areas of Hattah Lakes will respond to natural floods within one month of flooding, while positive responses to environmental water occur 1 to 3 months after inundation and are more restricted spatially. For environmental water planning, managers need to be aware of these differences. The implementation of new infrastructure to transport or retain environmental water on floodplains needs to be planned carefully, with continuous monitoring of rainfall and natural floods. Whilst environmental floods do not mimic the effect of natural floods, they do provide some positive benefits that can partially offset effects of reduced natural floods.

Automated summary

River floodplains are dynamic and diverse ecosystems, but they are at risk of degradation due to river regulation and climate change. Environmental water has been used to maintain their health by mimicking natural floods. This study used Landsat data to investigate the drivers of vegetation dynamics in the Hattah Lakes floodplain in Australia. The study found that the effects of environmental water on floodplain vegetation differed from those of natural floods in both space and time.