GPS based precipitable Water Vapor estimation for Rainfall forecasting

Abstract

Climate change has led to regional and local shifts in temperature, which significantly affected the water-holding capacity. This in turn has impacted precipitation patterns and increased the frequency of extreme weather events. Accurate estimation of atmospheric water vapor is essential for improving rainfall forecasting, climate monitoring and meteorological modeling. Traditional methods used in measuring Precipitable Water Vapor (PWV) are limited in spatial and temporal coverage, operational costs and provide intermittent data. The advancements in Global Navigation Satellite System (GNSS) technology have enabled ground-based GNSS to provide continuous observations for measuring precipitable water vapor in wide area and cost effective manner. This study used GPS-derived PWV data to enhance the forecasting of rainfall occurrences. The research assessed the accuracy of GPS-derived PWV against NCEP Reanalysis data, analyzed its spatial-temporal variations across the agro-ecological zones in Uganda, and derived a threshold PWV value associated with rainfall occurrence in different zones. RINEX files from 40 CORS across Uganda were used. The GNSS RINEX files were processed using GAMIT/GLOBK software to estimate Zenith Total Delay and derived PWV. The findings from the study showed that PWV varies depending the agro-ecological zones and the threshold PWV value in the different zones can be used for forecasting rainfall occurrences that strengthen early warning systems and aids in disaster preparedness, aligning with Sustainable Development Goal 13 (Climate Action).