Hebei Province, 1949–2000

Effective management of limited water resources in the North China Plain requires reliable calculation of historical groundwater balances at local, sub-watershed scales. These calculations typically are hindered by poorly constrained recharge estimates. Using a simple soil-water balance model, we independently calculated annual recharge from irrigated cropland to unconfined alluvial aquifers underlying Luancheng County, Hebei Province, in the western part of the North China Plain, for 1949–2000. Model inputs include basic soil characteristics and daily precipitation, potential evapotranspiration, irrigation, crop root depth, and leaf-area index; model outputs include daily actual evapotranspiration and areal groundwater recharge. Results indicate that areal recharge is not a constant fraction of precipitation plus irrigation, as previously assumed, but rather the fraction increases as the water inputs increase. Thus, model-calculated recharge rates range from 5 to 109 cm year1, depending on the quantity of precipitation and irrigation applied. The important implication is that, because this drainage recharges the underlying aquifer, improving irrigation efficiency by reducing seepage does not save water. This explains why successful efforts to reduce groundwater pumping for irrigation have had no effect on water-table declines. So long as crop cover is extensive and all crop-water requirements are met—which has been the case in Luancheng County since the 1960s—groundwater levels will continue to decline at a steady rate. Potential solutions include reducing the irrigated area, reintroducin