TAHMO In 2014, the Trans-African Hydro-Meteorological Observatory (TAHMO) was officially founded as a Dutch not-for-profit foundation. Now, five years later, TAHMO has become the largest provider of scientific weather and climate data for sub-Sahara Africa. The present network of 500 stations in 20 countries still falls well short of the final network of 20,000 stations but we should already consider TAHMO as a major success, as it has shown that it is possible to run a cost-effective observation network. TAHMO distinguishes itself through different approaches with respect to technology, operation, and financial sustainability. Innovations in all these aspects are needed to move forward and will be discussed in some detail during the presentation. Technology TAHMO has partnered with METER Group in the co-design of the current weather station. Originally, the thought was to develop a very cheap ($200) station ourselves but the engineering needed to move from a proof-of-concept to a fool-proof concept is more complex than one may think. Many ideas have been bounced between the two teams and tested in the field in Africa, leading to a third generation apparatus that is very robust. Operation Over 90% of TAHMO stations are placed at (secondary) schools. This provides some physical but especially social protection. Educational material is provided to engage teachers and students and to encourage them to help out with simple maintenance, such as cleaning. Also the IT backbone, developed with support through IBM's Corporate Social Responsibility activities is worth mentioning as it supports state-of-the-art QA/QC. Financial sustainability So far, most stations have been funded through projects funded by different donors and agencies. A large investment by IBM / Weather Underground formed the basis for a rapid expansion of 333 stations. To ensure long-term financial sustainability, TAHMO provides data services to commercial users. Clearly, value chains run from raw data to actionable information. Willingness to pay increases exponentially along that chain. For this reason TAHMO has become part of a network of entities that bridge the gap between weather station and information market.

Understanding of hydroclimatic processes in Africa has been hindered by the lack of in situ precipitation measurements. Satellite-based observations, in particular, the TRMM Multisatellite Precipitation Analysis (TMPA) have been pivotal to filling this void. The recently released Integrated Multisatellite Retrievals for GPM (IMERG) project aims to continue the legacy of its predecessor, TMPA, and provide higher-resolution data. Here, IMERG-V04A precipitation data are validated using in situ observations from the Trans-African Hydro-Meteorological Observatory (TAHMO) project. Various evaluation measures are examined over a select number of stations in West and East Africa. In addition, continent-wide comparisons are made between IMERG and TMPA. The results show that the performance of the satellite-based products varies by season, region, and the evaluation statistics. The precipitation diurnal cycle is relatively better captured by IMERG than TMPA. Both products exhibit a better agreement with gauge data in East Africa and humid West Africa than in the southern Sahel. However, a clear advantage for IMERG is not apparent in detecting the annual cycle. Although all gridded products used here reasonably capture the annual cycle, some differences are evident during the short rains in East Africa. Direct comparison between IMERG and TMPA over the entire continent reveals that the similarity between the two products is also regionally heterogeneous. Except for Zimbabwe and Madagascar, where both satellite-based observations present a good agreement, the two products generally have their largest differences over mountainous regions. IMERG seems to have achieved a reduction in the positive bias evident in TMPA over Lake Victoria.