Identification of the large-area and long-duration drought and its evolutionary characteristics in Nenjiang River basin

The effects of droughts on food, economic, and social security have long been a worldwide significant issue. Recently droughts have showed a development trendency with a longer duration and a wider impact area due to the climate change and the human activities. In this study, the Gravity Recovery and Climate Experiment (GRACE) satellite data were used to develop the water storage deficit index, based on which the large-area and long-duration drought (LLD) were identified using the theory of runs and the copula functions. In the Nenjiang River basin, two drought events with a joint distribution frequency of greater than 75 % were identified as LLD events, with a drought area of 29.7 × 104 km2 and a drought duration of 27 and 33 months respectively. In terms of drought characteristic indicators, the average values of drought intensity, drought severity, and extreme intensity for LLD events were 1.04, 31.71, and 2.30, which is significantly higher than for other types of drought events. The LLD events take a longer time to develop to the peak intensity than other types of drought events, but their drought centroid migration is more widespread. This suggests that the propagation process of the LLD events is more complex and the spatial and temporal distribution of drought is more uneven. Thus, we recommended that appropriate actions and regulations be adopted for different regions in different periods to reallocate water resources according to the drought-related losses and management expenses. This study introduces an identification method of the LLD events, combined with the analyses of evolutionary charaterisitics in space and time. It is hoped that the outcomes of the study can help watershed managers to clearly and conveniently identify the LLD events based on the predicted drought duration and area.