Reconstructing extreme hydrological variability over recent millennia in semi-arid northwest Australia

[Truncated] This thesis examines the long-term variability of hydrological extremes in the semiaridPilbara region of northwest Australia. The extent to which hydrological regimes havechanged in the historic past provides a critical baseline against which to compare thepotential impacts of present and future changes in hydroclimate, including those from anthropogenic-driven warming as well as land-use change. However, owing to the isolation of the Pilbara coupled with short and sparsely resolved instrumental records, comparatively little is known about regional rainfall patterns and recharge prior to the early 1900s. In this research, I thus sought to reconstruct periods of high rainfall and extended drought for the Pilbara over the last two millennia by integrating analyses of satellite imagery, instrumental data, documentary evidence and paleolimnological indicators.

The research focused on the Fortescue Marsh (local aboriginal name Martuyitha), the largest wetland of inland northwest Australia, which also acts as a terminal basin forone of the largest catchments in the region. I first developed a high-resolution record of inundation and drought for the Marsh over the last century. I used a monthly sequence of satellite images to quantify surface water expression on the Marsh between 1988–2012, which was then coupled with instrumental rainfall data at both local and regional scales to build a multiple linear model to reconstruct monthly history of inundations and droughts since 1912. Severe and intense regional rainfall events, as well as the sequence of recharge events both within and between years, determined surface water expression. A series of prolonged, severe and consecutive summer inundations occurred between 1999 and 2006, including the most severe inundation (~1200 km² in March 2000), which were unprecedented compared to the last century.