Sivapalan has introduced many hydrological concepts, theories, and research methods throughout his career. His academic career can be divided into three distinct phases.
Phase 1. Extrapolation Across Scales: Scale Issues in Hydrologic Predictions During his PhD studies and in the ten years afterward (1989–1998), Sivapalan devoted himself to research on scale issues in hydrological predictions. He organized successful workshops on scale issues in
Robertson, Australia, in 1993 and in
Krumbach, Austria, in 1996, which had a major impact on the field.
Phase 2. Extrapolation Across Places: Predictions in Ungauged Basins From1999 to 2008, Sivapalan focused on the development of hydrological models at the catchment scale. He approached the problem from the bottom up and top down. He and his doctoral student Paolo Reggiani proposed a/the thermodynamic theory framework to formulate balance equations for mass, momentum, and energy at the catchment scale and associated constitutive theory and closure relations that he introduced as a way to develop physically based hydrologic models of appropriate complexity and fidelity over what he called the representative elementary watershed (REW) scale. In parallel, he and students Chatchai Jothityangkoon and Darren Farmer proposed an alternative top-down, data-based methodology for the systematic development of models of appropriate complexity by focusing on reproducing signatures of hydrologic variability over a range of timescales. Recognizing the considerable uncertainty in hydrological predictions due to the inability to estimate transpiration by natural vegetation realistically, Sivapalan improved the research approach through
interdisciplinary synthesis. He and his PhD student Stan Schymanski proposed and tested the principle of vegetation optimality, and in particular the maximization of net carbon profit, as a way to make prediction of evapotranspiration and water balance with minimal calibration. Around 2001, Sivapalan turned his attention to the problem of Predictions in Ungauged Basins (PUB). He introduced the idea of PUB to the
International Association of Hydrological Sciences (IAHS), which launched PUB as a global, decadal (2003–2012) initiative, with Sivapalan as the founding chair. Sivapalan wrote the PUB science plan, organized several workshops and conferences, and traveled around the world to promote it and mobilize the community. Apart from its practical value, Sivapalan saw PUB as providing the basis for advancing a unified theoretical basis for catchment hydrology. The culmination of PUB was the publication of the landmark synthesis book Runoff Predictions in Ungauged Basins (Blöschl et al., 2013) by
Cambridge University Press, in which Sivapalan served as an editor.
Phase 3. Extrapolation Across Time: Predictions under Change and Socio-hydrology From about 2010, Sivapalan turned his attention to the problem of predictions under change, especially human-induced changes to the hydrologic systems. Through a series of meetings, he brought the hydrologic community together to develop a forward-looking agenda to deal with predictions under change. In 2011 he and his colleagues launched the sub-field of
socio-hydrology as a science that deals with the two-way feedback between humans and water. Change in Hydrology and Society, another global, decadal (2013–22) initiative of the
International Association of Hydrological Sciences in which once again Sivapalan played a leading role. He traveled around the world, establishing international collaborations in
Australia,
China, and
Europe, and promoting socio-hydrologic thinking. For his contributions to socio-hydrology and his leadership in promoting the field around the world he was awarded the
Prince Sultan Bin Abdulaziz International Prize for Water (PSIPW) (Creativity Prize). ==Awards and honors==