Drought impact-based forecasting: Trade-offs between indicators and impacts

Despite the progress in seasonal drought forecasting, it remains challenging to identify suitable drought indices for accurately predicting the impacts of a future drought event. In this study, we identified relationships across Europe between the forecasting skill of various drought indices and the estimated drought impacts. We calculated the indices over various accumulation periods, and assessed the forecasting skill of indices computed based on ECMWF’s seasonal forecast system SEAS5. An evaluation was performed by computing the same indices from the ERA5 reanalysis data and comparing them across various verification metrics, including deterministic Correlation Coefficients, MSE, RMSE, MAE, and probabilistic Brier and Rank Probability performance and skill scores. We further conducted a literature review of the studies assessing the performance of the indices in terms of estimating drought impacts across Europe. We finally performed a trade-off analysis and mapped the drought indices based on their drought forecasting and drought impact estimating skills at the NUTS1 regional level.

Our analysis reveals seasonal trends and spatio-temporal patterns in the forecast performance of drought indices with different accumulation periods computed from SEAS5 with various lead times. Overall, this analysis is a step forward to detect the most suitable drought indices for predicting drought impacts across Europe. Here, not only we present a new approach for evaluating the relationship between drought indices and impacts, we also resolve the dilemma of choosing the indices to be incorporated in the impact functions. Such scientific advancements are setting significant contributions to the emerging field of operational impact-based forecasting and operational drought early warning services.