Wetlands dependent upon local hydrological processes for their water requirements (e.g., rainfall, runoff and throughflow) are common in agricultural regions of Australia. They include listed threatened ecological communities, whose loss or degradation could greatly impoverish native biodiversity in the human-dominated landscapes they adorn. Lacking connection to large surface or groundwater flow systems that might buffer short-term hydrological perturbations, these wetlands are sensitive to climatic shifts. While their independence from large-scale water resources makes them a low priority for environmental water research, their simple hydrology makes them an ideal study system for understanding how wetland dynamics respond to climate-driven changes in water regime.
The Australian water plant functional group classification1 offers one prediction: under a drying climatic trend, rainfed wetlands could support greater vegetative species diversity and structural complexity, although this assumes their seed bank composition has adequate functional diversity to track changes in water availability. Ironically, this prediction implies increases in the taxonomic diversity and habitat values of rainfed wetlands, even as the climate that maintains them shifts toward a more precarious water balance. At some point, however, a drying climate must result in the loss of rainfed wetlands, at least temporarily. This raises some uncomfortable questions for how such transitions might be managed, given the importance of rainfed wetlands for native biodiversity and their prevalence on private land. Moreover, any long-term drying trend will likely be punctuated by multi-year sequences of greatly above and seasonally atypical rainfall - a nightmare scenario for predicting future wetland trajectories. Understanding how multiyear sequences of wet and dry periods might impact wetland hydro-ecology is a significant research challenge that a focus on rainfed wetland research might help address. Improved understanding of their ecological character and function, particularly their response to changing water availability, could inform management of all wetlands in an uncertain climate.