Causality of Sub-seasonal Extreme Precipitation in Arid and Semi-Arid Regions

Extreme precipitation (EP) events have intensified in arid and semi-arid regions due to climate change. Understanding the causal mechanisms driving EP at the sub-seasonal timescale is crucial for improving prediction accuracy and extending forecast lead times. This study investigates EP characteristics in Northwest China (ASRNC) and reveals through a composite analysis that EP is associated with specific atmospheric circulation patterns, including anomalous upper-level thermal and lower-level dynamic conditions. Moisture transport from the Indian Ocean, South China Sea, Mediterranean, and North Atlantic fuels EP events in different regions of the ASRNC. To quantify causal relationships, the extended convergent cross-mapping (CCM) method is employed. CCM outperforms traditional correlation analysis in capturing time lags and directional causality between variables. External circulation factors, such as geopotential height, zonal/meridional winds, outgoing longwave radiation, and specific humidity, exert influence through multifactorial interactions and teleconnections. Internal circulation factors, including surface, subsurface, and deep soil moisture (SWVL1, SWVL2, SWVL3), regulate local moisture cycling. Nevertheless, SWVL1 together with vapor pressure deficit is shown to have a stronger and shorter-term impact, while impacts of SWVL2 and SWVL3 are weaker. These findings provide a robust framework for identifying key drivers of sub-seasonal EP and offer valuable insights for disaster prevention and mitigation strategies as we as for improving future hydro-climatic scenarios in arid and semi-arid regions.