The impacts of global change in the humid tropics: selected rainfall-runoff issues linked with tropical forest-land management

Within the framework of IWRM, a major concern in the humid tropics is the effects of 'global warming' on the storm rainfall-runoff hydrology of both forests and converted forest lands. Further how such effects need to be incorporated within adaptive, forest-water-land management. But since the mid- 20th century, dramatic changes in land- use (LU) and land cover (LC) have also occurred which have led to rapid rates of deforestation and an expansion of land-forest degradation. How much these man-induced impacts have been influential on climate -water relations, as against the effects of inherent climate variability and predicted climate change scenarios, still remains a major challenge to quantify. Thus embedded within the global warming issue are these additional LU/LC change impacts on climate-rainfall-storm runoff across scales which also require consideration under the broader mandate of 'global change'. The work will initially succinctly summarize the existing uncertainties linked with both Global Climate Models (GCMs). Subsequently more detailed attention will be given to uncertainties linked with LC/LU change. The experiences of hurricane Mitch in Central America will then set the scene for an alternative strategy. A principle message is a call for more concentrated research effort on geographically the outer margins of the 'maritime continent' (centred on the Indonesian Archipelago) in the Western Pacific where tropical cyclone frequency is very high. This region presents a diversity of socio-economies and an opportunity to produce adapted forest-land management measures in preparation for future global change (warming and anthropogenic). Such measures can then be extrapolated to currently less frequently, affected areas from extreme events like hurricane Mitch. Examples from research in the tropical- cyclone prone, "Wet Tropics" of northeast Australia linked with the management of tropical rainforests and the adjoining sugar cane lands are then used to demonstrate these opportunities.