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It is crucial to investigate the characteristics of fire danger in the Beijing-Tianjin-Hebei (BTH) region to improve the accuracy of local fire danger monitoring, forecasting, and management. With the use of instrumental observation data from 173 national meteorological stations in the BTH region from 1991 to 2020, the fire weather index (FWI) is first calculated in this study, and its spatiotemporal characteristics are analyzed. The high- and low-fire danger periods based on the FWI occur in April and August, respectively, with significant decreasing and increasing trends throughout the BTH region over the past 30 years. Next, the contributions of different meteorological factors to the FWI are quantified via a detrending technique. Most regions are affected by precipitation during the high-fire danger period. Both the maximum surface air temperature (Tmax) and precipitation, however, notably contribute to the FWI trend changes during the low-fire danger period. Then, we assess the linkage with atmospheric circulation. Abundant water vapor from the Northwest Pacific and local upward motion jointly lead to increased precipitation and, as a consequence, a decreased FWI during the high-fire danger period. A lack of water vapor from the boreal zone and local downward movement could cause adiabatic subsidence and hence, amplify the temperature and FWI during the low-fire danger period. In contrast to shared socioeconomic pathway (SSP) 585, in which the FWI in the BTH region exhibits a north–south dipole during the low-fire danger period, SSP245 yields an east–west dipole during the low-fire danger period. This study reveals that there is a higher-than-expected probability of fire danger during the low-fire danger period. Therefore, it is essential to intensify research on the fire danger during the low-fire danger period to improve our ability to predict summer fire danger. [ABSTRACT FROM AUTHOR]

It is crucial to investigate the characteristics of fire danger in the Beijing-Tianjin-Hebei (BTH) region to improve the accuracy of local fire danger monitoring, forecasting, and management. With the use of instrumental observation data from 173 national meteorological stations in the BTH region from 1991 to 2020, the fire weather index (FWI) is first calculated in this study, and its spatiotemporal characteristics are analyzed. The high- and low-fire danger periods based on the FWI occur in April and August, respectively, with significant decreasing and increasing trends throughout the BTH region over the past 30 years. Next, the contributions of different meteorological factors to the FWI are quantified via a detrending technique. Most regions are affected by precipitation during the high-fire danger period. Both the maximum surface air temperature (Tmax) and precipitation, however, notably contribute to the FWI trend changes during the low-fire danger period. Then, we assess the linkage with atmospheric circulation. Abundant water vapor from the Northwest Pacific and local upward motion jointly lead to increased precipitation and, as a consequence, a decreased FWI during the high-fire danger period. A lack of water vapor from the boreal zone and local downward movement could cause adiabatic subsidence and hence, amplify the temperature and FWI during the low-fire danger period. In contrast to shared socioeconomic pathway (SSP) 585, in which the FWI in the BTH region exhibits a north–south dipole during the low-fire danger period, SSP245 yields an east–west dipole during the low-fire danger period. This study reveals that there is a higher-than-expected probability of fire danger during the low-fire danger period. Therefore, it is essential to intensify research on the fire danger during the low-fire danger period to improve our ability to predict summer fire danger. [ABSTRACT FROM AUTHOR]

The potential causes of megadroughts over North China (NC) in the preindustrial period were investigated using eight climate models evolved using CMIP5/PMIP3 and multiple proxy data. The full forcing experiments driven by both external forcing and internal variability show that megadroughts in NC were accompanied by extensive decadal drying over the Northern Hemisphere (NH), particularly in most of North America and Europe. The spatial pattern of hydroclimate matched well with the proxy-based illustration. However, such hydroclimate conditions over NH were difficult to reproduce in control experiments driven solely by internal variability. This finding suggests that external forcing may be a crucial factor leading to megadroughts in NC and simultaneous decadal drying over the NH. Moreover, external forcing may lead to climate cooling. Climate cooling weakened the pressure gradient from the West Pacific to East Asia and hence reduced the water vapor to land; meanwhile, local vertical downward movement occurred in the cooling climate background, which was unfavorable to air convection over NC. Both reduced water vapor and weakened air convection led to less precipitation. Meanwhile, there was a negative NAO, which intensified the eastward wave train at mid-latitudes. Consequently, the North American trough and European trough deepened, the northerlies in the post trough pattern intensified, and the water vapor from the high-latitude continent or polar areas was low, which was unfavorable to precipitation. This study implies that the megadrought in NC and simultaneous hydroclimatic spatial pattern over the NH may be underestimated in the CMIP5 climate prediction, which excludes external forcing. • Megadrought in North China co-occur with extensive dry anomaly over North Hemisphere. • The dry-anomaly hydroclimate pattern occurs in global cooling, declined water vapor. • Abnormal external forcing, e.g., volcanic eruption, is necessary for the dry-anomaly. • Effects of abnormal external forcing may be active through negative NAO pattern. [ABSTRACT FROM AUTHOR]

We identified regional differences over China of winter temperature response to large volcanic eruptions with different latitudes and seasons from 1956 to 2005, and investigated atmospheric circulations for corresponding spatial patterns of winter temperature anomalies using reanalysis data and simulations by the Community Earth System Model. Both observations and simulations show that spatial patterns of winter temperature anomalies over China are related to the latitudes and seasons of the eruptions. Tropical volcanic eruptions during summer led to winter temperature decreases of 0.4–1.6 °C in eastern China due to the increase of height gradient. Winter volcanic eruptions led to extensive warming over Tibet. Following summer volcanic eruptions at low latitude, there were warm winters in eastern China because of a weak Siberian high. An anomalous southerly wind caused slight warming over most of China following winter eruptions. With the typical "trough–ridge–trough" at high latitude of the Northern Hemisphere, the winter temperature decreased in northeastern China and increased in western China following summer eruptions at mid-latitude. However, temperature generally increased after winter eruptions. For summer eruptions at high latitude, winter temperature showed a coherent decrease over northwest and east-central China due to an intensified Siberian High and East Asian trough. The widespread warming occurred over China because of the meridional circulation between 65°N and 45°N was weaker following winter volcanic eruptions. [ABSTRACT FROM AUTHOR]