Why should we be concerned about water scarcity when presently only 10% of maximum available blue water and 30% of green water resources are used? The reason is the high variability of water resource availability in time and space (8). For example, the monthly mean discharge at the Obidos station in the Amazon River differs by a factor of 2 between the highest and the lowest months, even for climatologically averaged values. River discharge is more varia- ble in smaller river basins in general, and daily river discharge is, of course, more variable than monthly river discharge. Because of this temporal variability, it is impractical to use 100% of the available RFWR for human society. Flow during floods and wet seasons cannot be used during the low flow seasons unless storage systems are in place. That is why there are millions of artificial reservoirs, lakes, and ponds in the world and why most of the major rivers are regulated (9). Total capacity of this artificial storage is estimated to 7200 km3 (10), about twice the annual water withdrawal.Another reason that RFWR can be insufficient is its uneven spatial distribution.
đang được dịch, vui lòng đợi..