5. STATE-OF-THE-ART FOR PRECIPITATION-RUNOFF MODELLING

Precipitation-runoff (P-R) models that aim at predicting streamflow from the knowledge of precipitation over a catchment can be used for a wide range of applications to serve engineers and water managers in water related studies. This modelling exercise has received increasing attention since the end of the 50s, aided by the development of computing capacity. There is today a plethora of existing models but fully satisfactory solutions do not seem to have been found. No consensus exists today on how a P-R model should be developed, selected, assessed or implemented, although a huge amount of scientific papers provide methodologies to partly answer these questions. A few attempts were made to provide recommendations in the development and practical use of P-R models, especially for very simple models. But it seems that no comprehensive guideline devoted specifically to P-R simulation models exists today. However, many practical documents are available today that can be easily transferred/adapted to this modelling domain. The abundant scientific literature as well as previous comparative evaluation studies will also help to improve quality assurance procedures in the context of the HarmoniQuA project. Some aspects of these procedures may however depend on the type of practical application of the P-R model. 5.1 Definition of precipitation-runoff domain Precipitation-runoff (P-R) modelling attempts to establish a link between precipitation measured over the catchment and runoff (streamflow) observed at the considered outlet. The modelled system is the catchment, that is often considered as an adequate study unit for researchers and water stakeholders. The meteorological input denoted under the general term precipitation can be either rainfall or snowfall, grossly depending on air temperature conditions. Although precipitation and runoff can be considered as surface waters, the transformation of the first into the second at the catchment scale integrates many hydrological processes (such as interception, evapotranspiration, sub-surface flow, groundwater recharge, channel routing etc.), of which the most important take place underground (Beven, 2001). Today P-R models can be implemented in an operational context for many applications of hydrological engineering (e.g. water works design) and water resources management (e.g. floods or low flows forecasting, reservoir management). Because it focuses on the catchment, P-R modelling occupies a crucial place in water related studies. In the context of the HarmoniQuA project, it has therefore links with other domains. First, since the catchment cannot be considered as an impervious body and because there are exchanges between ground and surface waters, P-R is related to the groundwater domain. Second, in the context of the Water Framework Directive that focuses mainly on water quality issues, P-R modelling is important since a satisfactory