Trans African Hydro Meteorological Observatory (TAHMO)

Trans-African Hydro-Meteorological Observatory

Monitoring Africa's environment is an important challenge if the continent's resources are to be used in an optimal and sustainable manner. Food production and harvest predictions would profit from improved understanding of water availability over space and time. This project targets to have a dense network of 20,000 hydro-meteorological monitoring stations set up in sub-Saharan Africa. To make this feasible innovation in sensors will lead to low-cost stations. The combination of sensor, satellite and model data provides a very complete insight in the distribution of water and energy stocks and fluxes.


Presently, the African observation network is very limited. National governments and regional planners do not have the data to make proper decisions regarding investments in water resources infrastructure. Also in atmospheric and hydrological science the lack of ground data from this continent hinders the development of reliable weather and climate models.

Nowadays, a broad range of remotely sensed data is available through satellites. Combination of this spatially extended, course resolution data with models and reliable and abundant ground observations increases the value of the satellite data. The three components complement each other, when applied in a data assimilation framework. The ground observations are currently the weakest link in this framework.

A sensor network

The idea behind this project is to build a dense network of hydro-meteorological monitoring stations in sub-Saharan Africa; one every 30 km. This asks for 20,000 of such stations. By applying innovative sensors and ICT, each station should cost not more than $200. The stations would be placed at schools and integrated in the educational program. The data will be combined with models and satellite observations to obtain a very complete insight in the distribution of water and energy stocks and fluxes. Within this project we are currently working with students on designing and testing new and innovative ways to measure climate variables in a low cost way.


Benefits of this project are threefold.  Apart from monetary benefits through better anticipation on weather conditions, also scientific and social benefits are expected. In monetary terms, benefits are expected as a result of harvest predictions, which also enable more local and specific food aid.

Hydrological science can benefit greatly from combining the ground data with models and satellites. This leads to increased understanding of the hydrological system on large scales. It also enables better hydrological predictions for hydropower, irrigation, drinking water and flood warning and control.

By doing the roll-out through schools and integrating the weather stations in an environmental education package, social benefits can be realized. This enables children to learn about their environment and their connectedness to it.  An idea is to connect the weather stations to the XO-computer ($100 laptop) network. In this way, local data can be processed for local use, but also shared globally. At schools, the weather stations can be used for practical experiments to teach physics and an example case to teach applied mathematics.

TAHMO Sensor Design Competition

For this extensive and multi-dimensional project to be successful, the TAHMO team is convinced that local expertise and knowledge is essential to involve. The TAHMO Sensor Design Competition was one of the first steps towards building a community of people willing to assist and play an active role in the TAHMO project. This contest was run in 2013 at (mainly) African universities. The first round of the competition was open to any academic or research group in Africa and asked for the design of an innovative  robust sensor, capable of measuring a weather related variable. In total 26 designs coming from 15 different teams were received. The top thirteen teams with the best designs received a ‘Maker Package’, an extended electronics kit, that allowed them to build and test their sensors. Based on videos an pictures of their prototypes, the top eight teams were selected, resulting in twelve participants from Nigeria, Kenya, Uganda, Zimbabwe and Spain, attending the TAHMO Final Challenge together with water management professor Nick van de Giesen and MacGyver scientist Rolf Hut from Delft University of Technology, and Adam Gleave from the Raspberry Pi Foundation. This workshop was held from Monday 29 July to Friday 2 August 2013 in buzzing iHub in Nairobi, Kenya. During five days, 21 sensors brought by the participants, measuring variables such as rainfall, temperature, humidity and wind were integrated into an experimental weather station. All sensor were connected to one Raspberry Pi, a low-cost microcomputer, that functioned as the heart of the integrated weather station. The Raspberry Pi sent all data obtained by the sensors to the internet through MQTT, a messaging transport that is ideal for connecting small devices connected on networks with minimal bandwidth. IBM’s system Intelligent Operations for Water (IOW) stored the data from the 21 sensors in the cloud and nicely visualised measurement values on a map.   

A video and pictures of the TAHMO Final Challenge in Nairobi can be found here and on TAHMO’s Facebook page

Technical details

The sensors to be used in this type of weather stations need to be robust against dust and insects. The use of moving parts should be avoided, as this requires more maintenance and increases the risk of failure. Currently, we are working on rainfall measurement using an acoustic disdrometer. Also referred to as “measuring rainfall by the beat of the drum”.

Inexpensive Acoustic Disdrometer

It would be a hydrological understatement to say that measuring rainfall correctly is important. Recent years have seen important lowering of the costs of raingauges capable of measuring rainfall intensities. Such raingauges are typically tipping bucket raingauges, connected to an event logger. Costs for such a raingauge are about $100. Accuracy is not always very high, especially during high intensity storms. The moving parts make them vulnerable to slight disruptions such as insects. We set out to design a raingauge without moving parts and at a better price/quality ratio than existing raingauges.

After testing several potential candidates, we settled on a very simple piezo ceramic element, which measures the impact of single drops. Such an element costs around $1. The impact of each drop causes an acoustic signal that is transformed into a voltage. A typical impact gives an upswing of up to 1 V and the ringing lasts about 50 ms. With a surface area of about 20 cm², there is almost never overlap between the signals of different drops. The basic assumption is that each drop will have reached terminal velocity and that the total energy of the impact can, thereby, be related to drop size. We calibrated this acoustic disdrometer by letting drops of different size fall on the disdrometer. A very encouraging calibration curve was obtained in this way. Further testing consisted of comparisons during rainstorms between the acoustic disdrometer and standard tipping bucket raingauges. During intensive storms, the acoustic disdrometer gave results that were very close to those of a nearby totaling raingauge. The signal of the tipping bucket raingauges was clearly saturated as these were not capable of keeping up with the rain. During low intensity events, tipping bucket raingauges performed better as drops too small to detect by the acoustic disdrometer became a significant part of the total rainfall.

In first instance, a simple MP3 player with recording functionality ($50) was used as datalogger and processing was performed with a Matlab script. Presently, processing is done on-board of a simple custom built logger that logs the time and total energy of each drop. Post-processing converts the total energy to drop size and corrects for missing small drops by fitting the pdf’s to known raindrop distributions.

The Wiimote game-controller converted into a floating evaporation meter

For information on this topic, please check the following:


VARA Nieuwslicht item on Wiimote sensors

TAHMO in the media

TAHMO and its design competition popped up in various media. A short selection:

  • BBC Newsday: interview with professor Nick van de Giesen on the project and the design competition (audio)
  • Deutsche Welle: interview with professor Nick van de Giesen on the design competition (audio and text)
  • The Guardian (text)


The initiative is developed in cooperation with the International Water Management Institute (IWMI) and Oregon State University (OSU).

Further collaboration is welcomed, as well as financing.


Contact for more information: Nick van de Giesen