Spatial patterns of atmospheric vapour transport and their connection to drought in New Zealand

The impacts of drought can be substantial, particularly for primary producing nations such as New Zealand. Despite the importance of drought, identifying connections to atmospheric drivers remains a challenge. Vertically integrated water vapour transport (IVT) is critical to understanding the connection between ocean, atmosphere and the land surface, and as such the drivers of drought events. Self-organizing maps (SOMs) are used here to characterize the spatial patterns of IVT over New Zealand. In turn, the occurrence of these patterns during drought conditions (defined using the standardized precipitation and evapotranspiration index) across New Zealand is then identified and discussed. The resulting classification highlights a collection of high and low IVT magnitude nodes (i.e., spatial patterns). Low IVT nodes occur 40.57% of the time during all drought events and 45.86% during the top 99th percentile events. Conversely, high IVT magnitude nodes occur less frequently during drought events, at 23.77 and 20.96% of the time during all drought events and the top 99th percentile events, respectively. The low IVT nodes are also particularly dominant during summer and autumn season drought events. An increase in the frequency of occurrence of drought-associated nodes is observed over the course of the study period, which may in part be associated with El Nino-Southern Oscillation (ENSO)-driven interannual variability in New Zealand climate. Overall, the results demonstrate the importance of atmospheric circulation-driven disruptions in moisture transport for drought development, while also providing a first moisture transport weather classification for New Zealand.