Initiated in early 1990s, the International GNSS Service (IGS) has made significant contribution to the rapid development and global rampant new applications of the ever enhancing GNSS technology. One important area of these novelties is GNSS atmospheric sounding for climate and weather. The final IGS products routinely offer tropospheric zenith path delays with gradients with 4mm accuracy and 5minutes interval which can be an excellent source of information for meteorological research. Climate change and extreme weather are two major threats to the sustainability and prosperity of our society. Water vapor, as an important greenhouse gas, plays a very important role in atmosphere, climate and meteorology, especially in the formation, development and occurrence of extreme weather. Due to the rapid spatiotemporal variation chracteristics of water vapor and the limited availability of robust water vapor acquisition techniques, it has been a big worldwide challenge to develop high-quality, high-resolution, multi-sensor based robust water vapor detection method along with intensive investigation of relevant theory and algorithms in a systematic approach. The presence of water vapor in the troposphere can also lead to tens of meters range measurement error in GNSS satellite positioning and navigating. Precise determination of troposphere is therefore very important for the advancement of GNSS technology. This contribution will present selected results of our research in this regards in the past ten years, in particular GNSS+ multi-sensor technologies for near real-time monitoring and forecasting of severe weather and nowcasting. The March 2010 Melbourne/Australia storm was used as a case study and GPS observations from the state-wide CORS network in Victoria / Australia and IGS products are used. Different GPS data processing strategies are also investigated for the most robust precipitable water vapour determination. In addition to the ground-based GNSS as a main focus of study, a range of other state-of-the-art water vapour acquisition techniques including satellite to satellite tracking (e.g. GPS radio occultation), radiosonde, radar refractivity, synoptic weather station measurements and Australian numerical weather forecasting models are used to investigate the spatio-temporal variability of the troposphere.Our recent quest of relevant research will be introduced through a “retrospective” and “prospective” manner from both algorithm and innovative application points of view. The history, present work and future challenges of our major research effort through a multiple discipline approach, international collaboration as well as our new footprint in the context of the Chinese Natural Science Foundation initiatives will be summarised.