Changes in the drought condition over northern East Asia and the connections with extreme temperature and precipitation indices

Drought conditions are experiencing substantial changes due to global warming, but the contributions of changes in temperature, precipitation, and associated extremes to drought severity at the regional scale remain an important topic for climate change research. Northern East Asia (NEA) has experienced frequent climate extremes and is very sensitive and vulnerable to climate change. We analyze the spatiotemporal variations of the Standardized Precipitation-Evapotranspiration Index (SPEI) and 7 ETCCDI extreme climate indices (ECIs), the relationship between SPEI and ECIs, and the mechanism for SPEI changes during 1979–2018. Observations indicate a significant increasing trend in drought severity in NEA. Warm-related ECIs show a similar increasing trend, while precipitation-related ECIs (heavy precipitation days and extreme precipitation intensity) display no significant trend. Correlation analysis indicates that the intensification of drought in NEA is strongly related to the changes in average temperature and related ECIs, while the correlation with precipitation and related ECIs is weak and insignificant. A coupled model (CSIRO-MK3.6.0) simulation driven by realistic external forcing reasonably reproduced the observed NEA SPEI changes and the relationships with temperature, precipitation, and the related-ECIs. Attribution analysis is further conducted using the model simulations. The increased severity of NEA drought is attributed to remarkable increases in potential evapotranspiration (PET), caused by increases in surface net radiation and the vapor pressure deficit (VPD), and the VPD makes a more significant contribution to the decrease in SPEI. Increased PET intensifies the drought condition in NEA even though the moisture supply (precipitation) experiences no decrease trends during 1979–2018. The strong warming and increase in warm-related ECIs drive increases in the VPD, intensifying the evaporative demand and amplifying the drought conditions in NEA. Our findings highlight the connections between drought risks and intense warm extremes at regional scales and the potential role of external radiative forcing in causing these changes. • A significant increasing trend in drought severity is observed over northern East Asia in the recent four decades. • Drought in northern East Asia closely linked to changes in temperature and related extremes. • Coupled model driven by realistic external forcing has good capability in reproducing the drought change. • Increased evaporative demand leads to amplification of the drought conditions in northern East Asia under global warming.