Résumé
Global measurement of rainfall offers new opportunity for hydrological monitoring, especially for some of thelargest Tropical river where the rain gauge network is sparse and radar is not available. Member of the GPMconstellation, the new French-Indian satellite Mission Megha-Tropiques (MT) dedicated to the water and energybudget in the tropical atmosphere contributes to a better monitoring of rainfall in the inter-tropical zone. As part ofthis mission, research is developed on the use of satellite rainfall products for hydrological research or operationalapplication such as flood monitoring. A key issue for such applications is how to account for rainfall productsbiases and uncertainties, and how to propagate them into the end user models ? Another important question ishow to choose the best space-time resolution for the rainfall forcing, given that both model performances and rain-product uncertainties are resolution dependent.This paper analyses the potential of satellite rainfall products combined with hydrological modeling to monitor theNiger river floods in the city of Niamey, Niger. A dramatic increase of these floods has been observed in the lastdecades. The study focuses on the 125000 km2 area in the vicinity of Niamey, where local runoff is responsible forthe most extreme floods recorded in recent years. Several rainfall products are tested as forcing to the SURFEX-TRIP hydrological simulations. Differences in terms ofrainfall amount, number of rainy days, spatial extension of the rainfall events and frequency distribution of the rainrates are found among the products. Their impacts on the simulated outflow is analyzed. The simulations basedon the Real time estimates produce an excess in the discharge. For flood prediction, the problem can be overcomeby a prior adjustment of the products - as done here with probability matching - or by analysing the simulateddischarge in terms of percentile or anomaly. All tested products exhibit some skills in detecting the relativelyheavy rainfall that preceded the flood and in predicting that the 95th percentile of the discharge (i.e. the flood alertlevel in Niamey) will be exceeded.One outcome of the work is to show how different types of satellite information can be relevant and their scalescomplementing each-other for tropical hydrology. The red flood of the Niger river in Niamey is a good exampleof these scale complementarity. Satellite altimetry is needed to monitor the low frequency variation of the Nigeroutflow associated with early season rainfall far ahead of Niamey ; while high resolution satellite rainfall productsare needed to model the fast response to the rainfall occurring during the heart of the monsoon season near Niamey.