Leveraging ERA5-Land Reanalysis Precipitation Data for Urban Flood Vulnerability and Water Security Assessments: A Global Perspective

Abstract

Reliable datasets evaluating average and extreme precipitation are crucial for assessing water-sector vulnerabilities and adaptive capacity in global cities. However, conventional meteorological station data is often insufficient for consistent global analysis. In this study, we piloted and refined a publicly accessible decision-support tool (Global Urban Climate Assessment-GUCA) on 12 global cities using the ERA5-Land reanalysis precipitation dataset from the European Centre for Medium-Range Weather Forecasts (ECMWF). We analyzed data from water years 1981 to 2023 to assess flood exposure by examining trends in annual peak daily precipitation, transformed using the Standardized Precipitation Index (SPI) (z scores) and an estimate of 25-year return period precipitation. We also analyzed changes in water availability by analyzing linear trends in annual average precipitation z scores, and in untransformed annual averages. To evaluate water security in the 12 pilot cities, we combined average annual precipitation, standardized precipitation trends, freshwater withdrawal data, and population change. Our results show that several cities are experiencing significant precipitation changes. For instance, Panama City and Shenzhen showed increased flooding vulnerability over the past 20 years (71–83%), while Mogadishu, Amman, and Abuja were more susceptible to reduced water availability and intensifying droughts (23–32%). These findings demonstrate that innovative use of ERA5 reanalysis data can provide a comprehensive and self-consistent global resource for conducting analyses of different aspects of water security, offering policymakers and urban planners actionable insights for more informed decision-making across a broader range of cities worldwide.