Résumé
ORSTOM–IRD, a French research institution, has contributed during 80 years to the observation of various components of the hydrological cycle in diverse low-latitude regions. Initially devoted to the monitoring of large river systems in Africa, ORSTOM– IRD hydrologists started to instrument small catchments during the 1950s to address technical needs for developing infrastructures, with the aim of better understanding the processes controlling the local water cycle in various environments. Since the early 1990s ORSTOM–IRD hydrologists have been actively involved in so-called ‘Regional Hydroclimatology Projects’ (RHPs), which are large international programs intended to decipher the interactions between land surfaces and the atmosphere in tropical environments. Long-term observing programs arose from the RHPs and they now constitute a key tool for monitoring the evolution of the hydrological cycle in regions where safe access to water is still not guaranteed and threatened by the impacts of global change.