neither population size nor the size of economies necessarily covaries with river basin size nor do conflicts over water or complexities of interactions over space variations in geography and human occupation of river basins are great some such as those in central asia are in semiarid regions where water scarcities have become chronically severe and where crossborder governance has faced serious challenges in taking remedial actions others are facing the portent of their watersheds being below sea level as the oceans continue to rise from global warming