Long-Term Variability of Relationships between Potential Large-Scale Drivers and Summer Precipitation in North China in the CERA-20C Reanalysis

Lan Dai,Jonathon S Wright

doi:10.3390/atmos12010081

Abstract

Although much progress has been made in identifying the large-scale drivers of recent summer precipitation variability in North China, the evolution of these drivers over longer time scales remains unclear. We investigate multidecadal and interannual variability in North China summer precipitation in the 110-year Coupled ECMWF Reanalysis of the Twentieth Century (CERA-20C), considering changes in regional moisture and surface energy budgets along with nine circulation indices linked to anomalous precipitation in this region. The CERA-20C record is separated into three distinct periods according to the running climatology of summer precipitation: 1901–1944 (neutral), 1945–1979 (wet), and 1980–2010 (dry). CERA-20C reproduces expected relationships between large-scale drivers and regional summer precipitation anomalies well during 1980–2010, but these relationships generally do not extend to earlier periods. For example, a strong relationship with the Eurasian teleconnection pattern only emerges in the late 1970s, while correlations with the El Niño-Southern Oscillation and the Pacific–Japan pattern change sign in the mid-twentieth century. We evaluate two possible reasons for this nonstationarity: (1) the underlying atmospheric model may require strong data assimilation constraints to capture large-scale circulation influences on North China, or (2) large-scale drivers inferred from recent records may be less general than expected. Our analysis indicates that both factors contribute to the identified nonstationarity in CERA-20C, with implications for the reliability of seasonal forecasts and climate projections based on current models.

Highlights

Located along the northern edge of the East Asian summer monsoon (EASM), North China frequently experiences hydrological dry and wet extremes arising from anomalous EASM circulation patterns [1]
Correlations with the EU pattern are consistently weak until the mid-1970s and are only significant after 1980 (Figure 9c). These results show that relationships between these large-scale teleconnection patterns and summer precipitation in North China are nonstationary in the CERA-20C reanalysis, with the expected relationships only evident since the 1980s
We have evaluated the long-term variability of relationships between summer precipitation anomalies in North China and their potential large-scale drivers in the CERA-20C

Summary

Introduction

Located along the northern edge of the East Asian summer monsoon (EASM), North China frequently experiences hydrological dry and wet extremes arising from anomalous EASM circulation patterns [1]. Rainfall associated with the EASM in July and August accounts for roughly two-thirds of the total annual precipitation in North China [2,3,4]. North China has experienced frequent summer droughts and extreme precipitation events in recent decades, which caused immense damages to agricultural productivity, ecosystem health, and human lives and livelihoods [5,6,7,8,9]. Summer drought events have occurred relatively frequently in North China since the late 1970s, owing to a weakened EASM and the associated “North Drought-South Flood” pattern [11,12]. The decadal shift toward a weaker EASM around the end of the 1970s has been variously attributed to a phase shift of the Pacific decadal oscillation (PDO) from negative to positive [13,14], upper-

Results

Discussion

Conclusion