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1 GSF National Research Centre, D-85758 Neuherberg, Germany (e-mail: seiler{at}gsf.de)
2 Institute of Hydrology, Hohai University, Nanjing, P. R. China
Groundwater flow is steered by both the groundwater recharge rate and by discharge altitudes above or below sea level; it is further controlled by the hydraulic properties of the aquifer system and often contains a transient flow component affected by natural hydrologic processes. All present groundwater discharges have both recent (<100 years) and past groundwater recharge components (>100 years). The ratio of the present to the past groundwater recharge depends on the climate zone: it is large in humid and small in arid areas, hence at low recharge rates transient, and at high groundwater recharge rates steady-state conditions prevail. Developing groundwater management strategies while neglecting any transient response of groundwater resources, and conducted in sensitive recharge/discharge areas like dry lands, results in either over-estimates or under-estimates of safe yields of groundwater resources, and thus may lead to non-sustainable resource development. The consequence of this would be groundwater depletion and often also a deterioration of the hydraulic properties of the aquifer system by subsidence, which both take place only after a long period of time.
