Multi-Temporal Variabilities of Extreme Precipitation over Central Asia and Associated Planetary-Scale Climate Modes

Abstract

Arid- and semi-arid Central Asia is particularly sensitive to climate change. The changes in extreme precipitation in Central Asia stemming from climate warming are the subject of intense debate within the scientific community. This study employed a Morlet wavelet analysis to examine the annual occurrence number of extreme precipitation in Central Asia from May to September during the period of 1951–2005. Their modulating planetary-scale climate modes were identified by using linear regression analysis. Two major scales of the temporal variability were derived: 2–3.9 years and 4–6 years. The dominant variability was a 2–3.9-year scale and was associated with the negative phase of the Polar/Eurasia (POL) pattern. The 4–6-year scale provided a secondary contribution and was closely linked to the negative phase of the North Atlantic Oscillation (NAO). These planetary climate modes acted as precursors of extreme precipitation over Central Asia. The negative phase of POL directly contributed to a negative height anomaly over Central Asia, which was intimately related to extreme precipitation. In contrast, the negative NAO phase possibly manifested as a Rossby wave source, which was subsequently exported to Central Asia through a negative–positive–negative Rossby wave train.

Keywords

• extreme precipitation
• Central Asia
• the Polar/Eurasia pattern