Reduction of mid-summer rainfall in northern India after the late-1990s induced by the decadal change of the Silk Road pattern

Abstract

Variation of summer rainfall can pose substantial challenges to water resources and agriculture in northern India, which includes the most fertile land in India, i.e. the Ganges Plain. This study identifies a significant rainfall reduction in northern India during its peak rainy season (July and August) after the late-1990s, based on observational and reanalysis data since 1958. This rainfall reduction is about 0.86 mm d−1, equivalent to 8.3% of the climatological mean. We suggest that the decadal reduction of northern Indian rainfall is induced by the decadal change of the Silk Road pattern (SRP), which is an atmospheric teleconnection pattern along the upper-tropospheric Asian westerly jet. After the late-1990s, corresponding with the decadal phase shift of the SRP, there is a cyclonic anomaly over West Asia, which can reduce rainfall in northern India. Furthermore, this rainfall reduction is unprecedented since the beginning of the 20th century, when observational data are available. Possible roles of the lower-tropospheric circulation changes and the Atlantic Multidecadal Oscillation are discussed.