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China, one of the most populous countries in the world, has suffered the highest number of natural disaster-related deaths from fire. On local scales, the main causes of urban fires are anthropogenic in nature. Yet, on regional to national scales, little is known about the indicators of large-scale co-varying urban fire activity in China. Here, we present the China Fire History Atlas (CFHA), which is based on 19 947 documentary records and represents fires in urban areas of China over the twentieth century (1901-1994). We found that temperature variability is a key indicator of urban fire activity in China, with warmer temperatures being correlated with more urban fires, and that this fire-temperature relationship is seasonally and regionally explicit. In the early twentieth century, however, the fire-temperature relationship was overruled by war-related fires in large urban areas. We further used the fire-temperature relationship and multiple emissions scenarios to project fire activity across China into the twenty-first century. Our projections show a distinct increase in future urban fire activity and fire-related economic loss. Our findings provide insights into fire-climate relationships in China for densely-populated areas and on policy-relevant time scales and they contribute spatial coverage to efforts to improve global fire models.

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Dust deposition can supply nutrients to the ocean and affect phytoplankton growth. However, the impact of dust deposition on phytoplankton biomass in varying trophic regions remains poorly evaluated. The Northwestern Pacific is located in the downwind area of East Asian dust and includes eutrophic regions (Yellow Sea, YS; East China Sea, ECS), high-nutrient low-chlorophyll waters (subarctic Northwestern Pacific, SNWP) and low-nutrient low-chlorophyll waters (Northwestern Pacific subtropical gyre, NWPSG), which is an ideal region to explore the spatial heterogeneity of the dust fertilization effect. Here, the distribution and variation of dust deposition, high dust deposition events (HDDE) and Chlorophyll-a concentration (Chl-a, mg m-3) in the Northwestern Pacific during spring from 1998 to 2020 were investigated. The differences in the response of phytoplankton biomass (using Chl-a as a proxy) to HDDE in the YS, the ECS, the SNWP and the NWPSG were explored. Our results indicated that a large amount of dust was deposited into the Northwest Pacific during spring, resulting in numerous HDDE. The HDDE could stimulate the increase of phytoplankton biomass in the whole area of the Northwestern Pacific during spring. The response probabilities of Chl-a to HDDE were most significant (~80%) in the SNWP and the duration of response was the longest, even lasting for up to 40 days. While the response probabilities of Chl-a to HDDE were lowest in the YS and ECS (~65%), increasing from north to south, and most of the responses were less than 20 days. The response of Chl-a to HDDE was also detected in NWPSG, confirming the dust fertilization effect in oligotrophic waters, with response probabilities of 70% and duration less than 30 days. Overall, this study provides a more comprehensive understanding of the differences of phytoplankton response to dust deposition in varying trophic regions.

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Dust storms are one of the major disasters in arid and semi-arid regions. Understanding the impact factors is crucial for early warning and disaster mitigation. Many factors have been affecting the spatiotemporal patterns of dust storms. However, the relative importance of those factors to dust emissions in recent 40 years over the whole dust belt has not been well documented. This study explored the relative importance of those factors to the interannual variation in dust emissions over the whole dust belt. The difference in the primary contributors over two global warming phases was compared to investigate the association of dust emission trend with global warming. The results indicated that the wind regimes, such as the nocturnal low-level jet, were key factors to the wintertime dust emissions over the Sahel. The springtime dust storms related to cold air and cyclones primarily occurred in the southern coast of the Mediterranean and northwestern China. The cold high and heat low were typical mechanisms for the summertime dust emissions, which frequently formed in western North Africa, the Middle East, and northwestern Indian subcontinent. Whereas the land cover and drought conditions play significant roles in the relatively wetter regions, i.e., the southern coast of the Mediterranean, the Ustyurt Plateau, the northwest coast of Indian Ocean, the Thar desert and the Taklimakan desert. The wintertime global warming coincided well with the decreasing trend of dust emissions over the dust sources inland with a more significant effect seen in Asia. The positive anomalies of summertime dust emissions were primarily found over the dust sources in the low-lying coastal areas on the foot of high mountains. Understanding the relative importance of those drivers to dust emission trends and their variation under different warming periods can improve the prediction of dust storm evolutions and mitigate their impacts under future climate change.

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Heat-health risk is a growing concern in many regions of China due to the more frequent occurrence of extremely hot weather. Spatial indexes based on various heat assessment frameworks can be used for the assessment of heat risks. In this study, we adopted two approaches-Crichton's risk triangle and heat vulnerability index (HVI) to identify heat-health risks in the Northern Jiangxi Province of China, by using remote sensing and socio-economic data. The Geographical Information System (GIS) overlay and principal component analysis (PCA) were separately used in two frameworks to integrate parameters. The results show that the most densely populated community in the suburbs, instead of city centers, are exposed to the highest heat risk. A comparison of two heat assessment mapping indicates that the distribution of HVI highlights the vulnerability differences between census tracts. In contrast, the heat risk index of Crichton's risk triangle has a prominent representation for regions with high risks. The stepwise multiple linear regression zero-order correlation coefficient between HVI and outdoor workers is 0.715, highlighting the vulnerability of this particular group. Spearman's rho nonparametric correlation and the mean test reveals that heat risk index is strongly correlated with HVI in most of the main urban regions in the study area, with a significantly lower value than the latter. The analysis of variance shows that the distribution of HVI exhibits greater variety across urban regions than that of heat risk index. Our research provides new insight into heat risk assessment for further study of heat health risk in developing countries.

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