Variability, complexity and diversity: The geomorphology of river ecosystems in dryland regions

Dryland regions cover approximately 47% of the world's land surface (Middleton & Thomas 1997). The rivers that drain these regions show great diversity in their physical character. Our understanding of the processes and morphologies of 'dryland rivers' have increased with the recent reviews of these systems (Graf, 1987; Thornes, 1994; Reid & Frostick 1997; Tooth & Nanson, 2000; Tooth, 200). An evident trend in river research over the past 10 years has been the increased emphasis on studying large river systems, particularly ecosystems, stressing the interconnections between physical and biological components. Research on dryland rivers has followed a similar trend (Thomas, 1997): between 1982-1992 and 1993-2003 there was a 40% increase in the number of published scientific articles on dryland river geomorphology in 20 international and national journals concerned. Despite this, many of our beliefs about dryland river processes come from rivers in humid and temperate regions, transferred to dryland settings with often amusing consequences (see Nanson et al., 2002).