Hydrological forecasting model in Colombia: application to the Magdalena River

The development of a hydrological forecasting model is conditioned by the available data collected in the entire hydrological catchment for which discharge has to be predicted. The forecast quality not only depends on the available historical data but also on the continuously measured data that is necessary to update the model in real time according to the observed conditions. Consequently, the data type, their quality, reliability and the ease of data acquisition highly influence the final model choice. In Colombia, numerous catchments in the interior of the country are equipped with pluviometric and some of them with limnimetric stations but with often incomplete measurement series. For some catchments, temperature and evaporation data are also available but measured only on a sporadic basis. The acquisition of these data is often difficult, due to the accessibility, the size of the country and related costs. These factors have to be considered for the model development to ensure the use of representative and stable data. The present study analyses only one catchment, the one of the Rio Magdalena. It has been chosen for strategic and security reasons, in agreement with the persons in charge of the national hydrological service. For this catchment, the available data include water level measurements at different locations along the river (see the map in Section 3) and precipitation data measured at these limnimetric stations. The available stage-discharge relations are not reliable enough to build a discharge forecast model. A detailed measurement of the precipitation falling onto the catchment is difficult to carry out by conventional methods. The developed forecast models are of a so-called black-box type. They correspond to an autoregressive moving average model with exogenous variables. Each of them predicts river stages at a given point of the studied river. The explicative variables are either river stages or precipitation amounts, measured at the studied location or at other upstream stations. The forecast time step is one day and the forecasts are completed from one to five days ahead. The calibration of the model parameters is part of the model development process. For each limnimetric station, the resulting parameter values encode a model adapted to the available data and the considered forecast lag (time period between the forecast emission and the predicted event). In a first step, the developed models only include limnimetric data. In a second step, these models are further validated and affined considering pluviometric data. Models have been developed for all main stations of Rio Magdalena (see map at p. 24) but only the results for Barranca station are presented in details in this report. The obtained results can be considered as being good and reliable, as illustrated by the graphs and statistical tests presented in Section 5 and 6. A summary of the best model for each station and each forecast time lag given the available data i