Baseline Water Supply means how much water people are using vs how much surface water is available. If the amount of water being used is more than the amount of surface water available, the higher the stress. The map indicates this with dark red being the highest stress and yellow having the least stress. This may seem odd because we have just been learning about how central areas have the least water, this is because this map is measuring surface water usage only and towns in central Australia have low populations. Arid land means there is no surface water.