Northern Europe and Southeast and East Asia are regions with a summer aridity index of 5 or more, but the summer aridity index has a distribution of 5 to 11 in Northern Europe and of 9 to 108 in Southeast and East Asia. The ways that weeds flourish vary. In Southeast and East Asia, in contrast, weeding must be done frequently every year. Moreover, on the continent of Europe, glaciers have reduced the topography, creating flat landforms, destroying fertile ground and lowering its crop productivity.