Introduction

Hydrological forecasting is the prior estimate of future states of hydrological phenomena in real time, not to be confused with hydrological design-data computation (prediction)*. While the actual use of the words “forecast” and “prediction” is a matter of semantics or convenience, the substance of the technical activities connected with each is basically different. Both these activities require historical data (time series) and may use the same or similar methods of hydrological analysis and modelling. However, hydrological forecasting comprises additional technical activities connected with other hydrological and non-hydrological subjects, such as network design, data processing, remote-sensing techniques, telecommunications, operational use of computers, etc. In view of this, the subject of hydrological forecasting should not be viewed as one particular hydrological technique, but as an economic activity using many technological developments, both hydrological and non-hydrological. Thus a prior knowledge of hydrological analysis and modelling, of network design techniques, of telecommunications and remote-sensing systems, of on-line and off-line computer use, etc., is necessary if the activity of hydrological forecasting is to be exercised successfully and efficiently.