6:西北地区蒸发势与降丽量的关系 (Relation between annual rainfall and potential evaporation) 5000 4000 3000 三2000 G1000 200 400 600 1000 Annual rainfallmm0 1000 2000 3000 4000 5000 0 200 400 600 800 1000 Annual rainfall/mm Annual potential evaporation/mm 图6: 西北地区蒸发势与降雨量的关系 西北地区蒸发势与降雨量的关系 (Relation between annual rainfall and Relation between annual rainfall and potential evaporation potential evaporation )