Drought assessment in a changing climate with the joint deficit index

<p>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.</p><p>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.</p><p> </p>

Analysis of drought characteristics over Luanhe River basin using the joint deficit index

In order to describe the overall drought status objectively, a copula-based joint deficit index (JDI) was adopted for analyses of drought characteristics in Luanhe River basin. Monthly precipitation data from 1958 to 2011 selected from 26 rain-gauge stations were used for calculating the JDI. The JDI, which encompasses multiple deficit statuses over time scales from 1 to 12 months by using the 12-dimensional empirical copula, is shown to be capable of providing a comprehensive and objective assessment of droughts. In addition, it is demonstrated that both emerging and prolonged droughts can be captured by the JDI. Results of the drought evaluation over the Luanhe River basin indicate that the frequency of drought occurrence generally increases from northwest to southeast, and droughts observed in summer and autumn are more frequent and severe. Compared with the northwestern part of the area, the drought events in the southeast are characterized by longer duration and greater severity. Furthermore, a general tendency of drying is found in the flood season (July to September) over the basin, with significant aggravating trends in the southeastern part. These related drought characteristics could provide valuable information and references for regional mitigation strategies and water resource management.