Empirical Subseasonal Prediction of Summer Rainfall Anomalies over the Middle and Lower Reaches of the Yangtze River Basin Based on Atmospheric Intraseasonal Oscillation

Abstract

Abstract:The middle and lower reaches of the Yangtze River basin (MLRYB) are prone to flooding because their orientation is parallel to the East Asian summer monsoon rain belt. Since the East Asian summer monsoon presents pronounced intraseasonal variability, the subseasonal prediction of summer precipitation anomalies in the MLRYB region is an imperative demand nationwide. Based on rotated empirical orthogonal function analysis, 48 stations over the MLRYB with coherent intraseasonal (10-80-day) rainfall variability are identified. Power spectrum analysis of the MLRYB rainfall index, defined as the 48-station-averaged intraseasonal rainfall anomaly, presents two dominant modes with periods of 20-30 days and 40-60 days, respectively. Therefore, the intraseasonal (10-80-day) rainfall variability is divided into 10-30-day and 30-80-day components, and their predictability sources are detected separately. Spatial-temporal projection models (STPM) are then conducted using these predictability sources. The forecast skill during the period 2003-2010 indicates that the STPM is able to capture the 30-80-day rainfall anomalies 5-30 days in advance, but unable to reproduce the 10-30-day rainfall anomalies over MLRYB. The year-to-year fluctuation in forecast skill might be related to the tropical Pacific sea surface temperature anomalies. High forecasting skill tends to appear after a strong El Niño or strong La Niña when the summer seasonal mean rainfall over the MLRYB is enhanced, whereas low skill is apparent after neutral conditions or a weak La Niña when the MLRYB summer seasonal mean rainfall is weakened. Given the feasibility of STPM, the application of this technique is recommended in the real-time operational forecasting of MLRYB rainfall anomalies during the summer flooding season.

Verification of High-Resolution Medium-Range Precipitation Forecasts from Global Environmental Multiscale Model over China during 2009–2013

“…The climate across Mainland China varies significantly due to the complex landscape with drastic changes in topography from the east to the west. Therefore, the methods used to divide sub-regions in China were proposed in terms of spatial differences [34,35]. In this study, to better detect the geographical distribution of the model skill and to distinguish the differences of average annual precipitation, climate and landscape among regions, the study domain is divided into nine drought sub-regions following [36] (Figure 1).…”

Extended-Range Forecast of Winter Rainfall in the Yangtze River Delta Based on Intra-Seasonal Oscillation of Atmospheric Circulations

“…This anomalous anticyclone caused by a combined effect of the local air-sea interaction mechanism is one of the possible cases of rainy winters [6]. In addition, intra-seasonal modes can also alter large-scale circulation and cause winter precipitation anomalies [7][8][9][10][11]. For example, the long-lasting rain and snow disaster in January 2008 lasted for more than 20 days.…”

Modulation of the intraseasonal variability in early summer precipitation in eastern China by the Quasi-Biennial Oscillation and the Madden–Julian Oscillation

“…This study aims to explore the impact of the tropical MJO on the summer rainfall in China and its modulation by the QBO. An exploration of the impact of the MJO on early summer rainfall and its modulation by the QBO can further improve our understanding of the summer rainfall variability to therefore provide a better forecast of summer rainfall especially on the long-range timescale (Li, 2016;Zhu et al, 2017;Liang et al, 2019).…”