Influence of boreal summer intraseasonal oscillation on rainfall extremes in southern China

Abstract

How boreal summer intraseasonal oscillation (BSISO) modulates the probability and spatial distributions of extreme rainfall occurrence over populous southern China was examined, using the newly proposed BSISO indices and two high‐resolution rain‐gauge‐based rainfall datasets in China. The probability density function of May–August rainfall in southern China is skewed towards large values in phases 2–4 of the first component and in phases 5–7 of the second component of BSISO life cycle, during which the probability of extreme rainfall events at the 75th (90th) percentile increases by 30–50% (over 60%) relative to the non‐BSISO period. The devastating floods with prolonged extreme rainfall in southern China over the three past decades occurred coincidently with these BSISO phases. The first component of BSISO, associated with 30–60‐day eastward/northeastward‐propagating ISO, is more favourable for the rainfall extreme over in‐land China. In contrast, the second component of BSISO, related to the 10–30‐day northwestward propagating ISO, tends to link with the rainfall extreme along the southeast coast of South China. Moisture budget indicates that the favourable environment for rainfall extreme is associated with southwesterly moisture convergence over southern China, while the moisture advection contributes insignificantly. This study suggests a potential for monitoring and probabilistic prediction of extreme rainfall events in southern China based on the real‐time BSISO indices.

Simultaneous modulations of precipitation and temperature extremes in Southern parts of China by the boreal summer intraseasonal oscillation

“…The BSISO influences on precipitation in the Yangtze River Valley are fulfilled via modulating the position of the western Pacific subtropical high (Ren et al 2013;Lu et al 2014). Precipitation extremes also show close relationship with two BSISO components (Hsu et al 2016;Gao et al 2016). For instance, both Lu et al (2014) and Zhu et al (2003) revealed that floods in the Yangtze River Basin during 1998 were in tandem with the active phase of 30-60-day BSISO.…”

“…Before being released, this dataset went through rigorous quality control procedures by the Climate Data Center (CDC) of the National Meteorological Information Center (data and documents available online http://cdc.cma.gov.cn/home.do), China Meteorological Administration (CMA). Extreme precipitation and extreme high temperature mainly concentrate during the period from May to August in southern parts of China, due to influences of East Asian summer monsoon (Ding and Chan 2005;Hsu et al 2016). So May-August is selected as the study period.…”

“…1 Percentage changes (%) in occurrence probability of precipitation extremes (left column) and extremes of daily maximum temperature (right column) during active phases of the BSISO1 against inactive BSISOs. Following the method introduced by Hsu et al (2016), for phase-i, the percentage change is calculated as…”

“…Inspired by the famous MJO index (Wheeler and Hendon 2004), Lee et al (2013) constructed BSISO indices to achieve purposes of realtime detection, monitoring and prediction of BSISOs. Derived BSISO indices show excellent performances in portraying distinctive periodicities and propagation routes of different agents (Hsu et al 2016). In sharp contrast to indirect impacts of the MJO on subtropical weathers, BSISO-induced circulation-convection pairs could invade into the subtropics, directly alter local background circulations, and further trigger weather anomalies or even extremes there (Yang et al 2010;Oh and Ha 2015).…”

A comprehensive analysis of coherent rainfall patterns in China and potential drivers. Part II: intraseasonal variability

“…The effect of the BSISO on precipitation in China has been described for specific regions and for individual rainfall events (e.g. Yang and Li 2003;Zhu et al 2003;Mao et al 2010;Gao et al 2013;Liu et al 2014;Li et al 2015;Hsu et al 2016). Previous studies have also linked subseasonal wintertime precipitation variability to the MJO (Liu and Yang 2010;Jia et al 2011;He et al 2011).…”