Unstable relationship between tropical Indian Ocean SST and spring drought on the Loess Plateau modulated by interdecadal variability of ENSO

Abstract The Loess Plateau (LP) is recognized as a region highly vulnerable to climate change, particularly susceptible to spring droughts. Spring drought intensity is crucial as it significantly impacts crop growth and the occurrence of dust storms. However, the underlying mechanisms of spring drought in LP remain unclear. This study investigates the relationship between spring drought intensity in the LP and interannual sea surface temperature anomalies (SSTAs) in the tropical Indian Ocean (SST_TIO). We found that this relationship is negatively correlated but exhibits instability. It was significant during 1963–2001, a time characterized by homogeneous SST_TIO changes, and became insignificant during 2002–2021, during which SST_TIO changes were inhomogeneous. Homogeneous SST_TIO changes appear to stimulate atmospheric wave trains emanating from North Africa and the Arabian Peninsula, influencing precipitation patterns in the LP via the anomalous height in Northeast Asia. In contrast, inhomogeneous SST_TIO changes do not have this effect. Additionally, the impact of homogeneous SST_TIO changes on LP's spring precipitation during 1963–2001 was slightly enhanced by synergistic SSTAs in the tropical eastern Pacific-Atlantic oceans. sensitivity experiments of numerical model confirm the above physical processes. Moreover, these synergistic changes in the TIO and tropical Pacific-Atlantic are modulated by the interdecadal variability of the preceding winter El Niño-Southern Oscillation (ENSO). SSTAs in Indian Ocean exhibit more homogeneous distributions and a closer linkage with tropical Pacific-Atlantic during the periods with stronger ENSO variability. Conversely, when ENSO variability is weak, inhomogeneous SSTAs of Indian Ocean have a weaker relation with tropical Pacific-Atlantic regions.