On 18 September 2024, the International Telecommunication Union (ITU), together with the European Cooperation in Science and Technology (EU COST) Action OPENSENSE held a Round Table on the Global Microwave Link Data Collection Initiative (GMDI) which took place at the ITU Headquarters in Geneva, Switzerland.

The meeting was motivated by the potential of opportunistic weather sensing, namely, microwave wireless links—commonly known as commercial microwave links (CMLs)—which can provide valuable rainfall estimates (Messer et al. 2006). Widely utilized in cellular backhaul networks, CMLs have significant potential to complement traditional rainfall observations and help bridge observational gaps in data-scarce regions, particularly in low- and middle-income countries. Although mobile network operators (MNOs) around the world collect these data to control and maintain their networks, it has so far only been used in meteorology and hydrology in a limited number of research projects, as data sharing remains a major challenge. Positively, a number of studies have taken place in developing countries in the Global South.

The event’s objective was to establish fundamental principles of a global initiative for collection and curation of signal level data from CMLs and their utilization in meteorology and telecommunication and to provide solutions to relevant pitfalls such as privacy and security concerns. GMDI was proposed by the EU COST Action OPENSENSE as a framework that would support MNOs when establishing data collection systems and provide a robust infrastructure for secured and controlled sharing of CML data and their long-term storage. Representatives from the industry (CML vendors, MNOs), the Global System for Mobile Communications Association (GSMA), the national meteorological services, the WMO, the ITU, and researchers from the academic sector met together to discuss the initial steps of this initiative.

The morning sessions consisted of dedicated lectures on the use of microwave link data for meteorology and hydrology and on the GMDI technical solution (see the online supplemental material) followed by moderated discussions. During the discussions, statements of all stakeholders were collected and topics crucial for GMDI success were identified. Experiences from countries where MNOs have been collaborating with researchers on CML rainfall retrieval projects show that the data can be accessed either through a network management system at, e.g., 15-min resolution with latency from several hours to a day (Messer and Sendik 2015) or via a custom-made SNMP-based application at a minute resolution with latency not exceeding a minute or two (Chwala et al. 2016). Estimated CML rain rates can be sufficiently accurate to be used, e.g., for weather radar adjustment (Graf et al. 2023), nowcasting (Imhoff et al. 2020), or hydrologic modeling (Pastorek et al. 2023). However, transitioning this technology into a widely adopted observation method and scaling it up to a continental scale poses a significant legal and organizational challenge and requires sustainable business models or incentives. The approach to these challenges was further discussed in breakout rooms during the afternoon session.

All stakeholders recognize the potential of CMLs as tools for rainfall estimation in meteorology and hydrology and agree that a coordinated effort is necessary to ensure the technology can be scaled up. The meeting resulted in four main areas of focus for initial GMDI activities, which will endeavor to pursue by the participants:

• Standardization: Development of an ITU recommendation on CML data collection and sharing.

• Contribution to relevant WMO technical documents by submitting a pilot project leveraging on OPENSENSE past achievements and proposing best practices of CML-based rainfall retrieval based on a specific case study.

• Incentives to MNOs: Identify use cases demonstrating potential cost savings in network optimization and business opportunities while seeking funding to cover direct costs associated with CML data sharing (incentives for MNOs joining GMDI).

• Technical solutions supporting CML data collection: MNOs and vendors that participated in the round table will assess the viability of enhanced CML data collection and transfer via network management systems to reduce barriers related to appropriate configuration and network security.

Overall, the event provided space for the first in-depth discussion between researchers, meteorological services, mobile industry stakeholders, and regulators. We will pursue the four focus activities and acquire the necessary funding for this operation. The status will be reported by OPENSENSE Action during online meetings later in 2024 and a face-to-face meeting in spring 2025.