Drought assessment in a changing climate with the joint deficit index

The characterization of droughts is very dependent on the time scale that is involved. To obtain an overall drought assessment, the cumulative effects of water deficits over different times need to be examined together. For instance, the joint deficit index (JDI) is based on multivariate probabilities of precipitation over various time scales from 1- to 12-months, and was constructed from empirical copulas. We examine the Gaussian copula model for the JDI, and we model the covariance across the temporal scales with a two-parameter function that is commonly used in the specific context of spatial statistics or geostatistics. The validity of the covariance models is demonstrated with long-term precipitation series.

Next, we assess the impact of climate change on future droughts, based on the JDI. We select an ensemble of CORDEX regional climate model simulations, under the emission pathways RCP4.5 and RCP8.5. The CORDEX resolution used is 0.11 degree (EUR-11). In particular, distributional changes in the JDI are analysed for the Brussels-Capital Region. This area contains climatological and synoptic stations that are operated by the Royal Meteorological Institute of Belgium, with long-term series.