A study on precipitation trend and fluctuation mechanism in northwestern China over the past 60 years

Abstract

This paper focuses on the mechanism of the trend and oscillation in precipitation records in northwestern China over the past 60 years. The results from regression and orthogonal wavelet decomposition show a clearly ascending in annual precipitation since 2000, which is contributed mostly by significant increase in autumn and winter precipitations, while almost no trend can be identified in spring and summer time, which shows a weak descending in non-linear form. This may be in connection with different warming rates in seasons. There is a significant anti-correlation between the precipitation and the North Atlantic oscillation (NAO) on the inter-annual scale. About 80% of their variances concentrate on inter-annual and multi-decadal scales. The multi-decadal components of NAO index have a phase leading about 10 years to corresponding precipitation, about 4-5 years leg for AMO. Hence, NAO index can be used as an indicator for inter-decadal change of the precipitation. Other results from combination-difference analysis show that the NAO in extreme negative phase could lead to the precipitation increase in central Asia and northwestern China, owing to increase in eastward water-vapor transport from south Europe to Northwestern China, which causes an increase in column water vapor content in the above areas, and meanwhile the transient eddy activity becomes intensified in the areas or north with a further south route moving from Europe, Central Asia throughout northwestern China. On the contrary, a dry climate might appear in the areas when meet extreme positive phase of NAO. Thus, NAO's oscillation is one of the most important mechanisms for inter-annual change in precipitation of northwestern China.