Hydrological processes in tropical Australia: Historical perspective and the need for a catchment observatory network to address future development

Tropical Australia. Streams and rivers of the Australian tropics have been the subject of substantial hydrological process research spanning the last 50 years. In this review, we highlight initial efforts to understand the hydrological response of forested ecosystems in the humid tropics, and how this has been more recently followed by work in savannas of the seasonal tropics. We describe recent findings from modelling and tracer studies and derive a framework of dominant hydrological processes for the region. We also detail five critical knowledge gaps that will require further attention with climate change and ongoing interest in development in the region. We outline the diversity of runoff generation mechanisms that prevail in the region and emphasise the role of connected wetlands and floodplains in catchment response. We discuss the prominence of focused, episodic recharge in the replenishment of groundwater stores across the region. We also review how climate change and potential water resource development projects may alter the hydrology of northern Australian catchments. Future research should focus on improving our physical understanding of key hydrological processes, as well as anticipate the likely effects of development and climate change on these processes. Intensive and long-term studies of experimental observatories, which capture the diversity in landscapes and climates of the region, will help frame sustainable water development policies in northern Australia.