In the northeastern Empty Quarter, sands highlight the region, being the largest expanse of sand in the world. It receives little to no rain for extensive periods of time. Little vegetation grows here either. The central highlands are drier than the western highlands because of rain-shadow influences, but still receives sufficient rain in wet years for extensive cropping. Its diurnal temperature variations are among the highest in the world: ranges from in the day to at night are normal. Water storage allows for irrigation and the growing of wheat and barley while the western highlands are famous for sorghum, coffee, and some tropical fruits like bananas and mangos.