New worldwide hydrological initiative needed



This essay argues for a new, decade-long worldwide hydrological initiative to permit change in the paradigm that underlies hydrological design and management. It is stimulated by the fact that over the last 20 years there has been a distinct change in our understanding of the nature and origin of the statistics of hydrological variables as measured in an individual watershed or region. The assumption was that these statistics are entirely haphazard in nature and indeterminate in origin, and do not change with time.Thus the most important hydrological variables (such as precipitation, runoff, and potential evaporation) are sampled over a calibration period (of perhaps only a few decades), and the statistics observed within that calibration period are used as the basis for hydrological design and water resource management. Now, however, there is increasing realization that the nature of the locally observed statistics of hydrological variables may be significantly determined by global-scale phenomena and might be prone to long-term change.