Investigation of Precipitable Water Vapor (PWV) and heavy rainfall relationship over Cyprus using CyMETEO infrastructure

The Eastern Mediterranean region is one of the most prominent hot spots of climate change in the world and extreme weather and climatic phenomena in this region such as heavy and extreme precipitation events are expected to become more frequent and intense. Water Vapour is the most abundant of greenhouse gases (accounting for ~70% of global warming) and is a direct indicator of severe weather events such as heavy precipitation and floods as it can change rapidly. To improve nowcasting of local heavy rainfall and flash storm events we need Precipitable Water Vapour (PWV) data. PWV is the amount of water potentially available in the atmosphere for precipitation, vertically integrated and it is a valuable predictor for weather forecasting. In Cyprus and globally PWV data are sparse and inhomogeneous. One technique to estimate PWV is by exploiting the propagation delay of the GNSS (Global Navigation Satellite System) satellites signals.

CyMETEO GNSS network installed in the frames of strategic infrastructure project “Cyprus GNSS Meteorology Enhancement” (CYGMEN) aims at developing a GNSS-based PWV monitoring system, incorporated at the CyMETEO portal, that will be used for short-range weather forecasting and extreme weather events investigation over Cyprus. To perform the GNSS-based PWV product validation of CyMETEO, we created a complete dataset on heavy precipitation events over Cyprus for the 12 CyMETEO stations from 2020-2024, based on data form the Cyprus Department of Meteorology (CY DoM) and from the European Severe Weather Database (ESWD). Heavy precipitation days are considered the days with precipitation ≥ 20 mm (Lazoglou et al. 2024, Zittis et al., 2020, Tymbios et al., 2010). This is the criterion we chose to categorize a precipitation event as day with heavy rain. From these cases we selected certain extreme events with rain ≥ 40mm, which were used to perform the validation of GNSS derived PWV and ZTD (Zenith Tropospheric Delay) employing radiosonde data from CY DoM. The GNSS tropospheric products (PWV, ZTD) were validated by utilizing existing independent datasets, such as ERA5 Reanalysis, Microwave Radiometer and Radiosonde data, during the selected extreme precipitation events. Additional extreme precipitation indices as well as the relationship between PWV and precipitation during the selected extreme precipitation events over Cyprus during the period 2020-2024 were also investigated.