Advances in drought monitoring using an operational hydrological model

Recent improvements of the hydrological, open source (OS) LISFLOOD model aimed to support both flood- and drought-related applications. The latest model upgrades are very promising for drought monitoring use cases, for which the sources of improvements can be grouped into four main areas: (i) updated meteorological forcings improving the quality of the gridded model inputs; (ii) revised static maps providing an improved representation of catchment morphology and soil properties; (iii) structural model revisions that enhance the physical consistency of simulated water fluxes; and (iv) the adoption of a new calibration objective function, the Joint Divergence Kling–Gupta Efficiency (JDKGE), which improves low-flow performance while maintaining or improving accuracy for high flows compared to the previous calibration using the Kling–Gupta Efficiency.

In this study, we evaluate the cumulative effect of these developments with a focus on drought monitoring and forecasting applications. Using multi-source observational data and different benchmarking strategies, we evaluate the accuracy and physical consistency of the new operational LISFLOOD model setup of the European and Global Flood Awareness Systems (EFAS version 6 and GloFAS version 5) of the the Copernicus Emergency Management Service (CEMS). The evaluation focuses on two key hydrological variables for drought monitoring, namely river flows and soil moisture, at the European and global scale. Beyond the two raw variables, we examine the performance of drought indicators, including the Low Flow Index and Soil Moisture Index from the European and Global Drought Observatories (EDO and GDO), and assess their ability in detecting drought events, using both hazard observations and impact data as reference. Results from long-term simulations show substantial improvements in drought detection thanks to the new developments in OS LISFLOOD and associated CEMS setups. Similar improvements in drought forecasting skill are also anticipated and will be investigated in further work.