| Inner Mongolia is an important natural ecological barrier in northern China.The forest and grassland have a large area of coverage,continuous distribution,high flammable material reserves,and high fire risk.The area burned by fire in Inner Mongolia is one of the highest among all the provinces in China.However,there are few studies about fire risk assessment in this region.Here,we analyzed the distribution patterns of burned areas and firespots in Inner Mongolia using MCD45A1 burned areas and MOD14A1/MYD14A1thermal anomalies data during the period 2002–2016.With this data,the spatial and temporal distribution of fire in Inner Mongolia were analyzed.From the perspective of natural factors and human activities,we selected eleven factors affecting the occurrence and spread of fire and established the fire risk assessment index system.Then,we analyzed the distribution of environmental factors and explicitly quantified relationships between fire and environmental features.On this basis,we built the fire risk assessment model with classical theory about risk analysis and analytic hierarchy process and divided the level of disaster regionalization.The results showed that:?1?The burned area extracted from Landsat remote sensing data and MCD45A1product for three grassland fires and one forest fire were compared.The error rates of the burned areas of the two were 9%,14%,21%and 22%.This showed that the MCD45A1fire product data had good accuracy and applicability for fire monitoring in Inner Mongolia.?2?The total burned area in Inner Mongolia over the 15-year period analyzed was46,300km2 while the total number of firespots was 13,488.However,there were large differences in burned area and number of firespots by year.The annual variation of burned area and number of fire points were quite different.The burned area present a down trend in fluctuation while the number of fire points showed an upward trend during the fifteen years studied.In general,the fire condition in Inner Mongolia was reduced.The happening of fire showed seasonal variations,which autumn and spring were high-incidence season,especially the months of February,March,April,May,August,September and October.The spatial distribution of burned area and firespots gradually decreased from northeast to southwest and the high density areas were mainly distributed in the border region between China and Mongolia,the forest-grassland belt and typical arable zones.The maps of fire distribution in each year showed areas of high annual recurrence of fires,such as in the east of the study area.The fire-burned areas and number of firespots in Xing'anling mountainous and the hilly regions,Hulunbei'er plateau and the hilly regions,and Xilinguole Plateau accounted for 90%of the total in the seven ecological zones of Inner Mongolia,with area and number ratios of 52%,28%,10%and 52%?17%and 12%,respectively.The fire-burned areas and number of firespots ranked from large to small were in the sequence of agriculture land,woodland,pasture land,and other land use types in the study area,with area and number ratios of 65.0%,25.3%,9.1%and 85.7%,7.6%,5.8%,respectively.Forest fires showed a decreasing trend,while grassland fires showed an increasing trend during the period in study area.?3?A pool of 11 variables were extracted from several databases covering physical and human aspects in order to establish the fire risk assessment index.The variables were selected considering both their potential relevance for fire occurrence,based on both extensive literature review and experts'knowledge,and their availability at the Inner Mongolia level.On this basis,we explicitly quantified relationships between firespots and environmental variables.The number of firespots had a normal function to NDVI in fire season.It was found that the number of firespots increased at first and then decreased with the rise of NDVI and vegetation water content.Fire easily occurred in areas with NDVI between 0.3 and 0.5 and vegetation water content between 0 and 0.3kg·m-2;The number of firespots showed double-peak structure with the temperature in fire season while the number of firespots had a normal function to precipitation anomaly in fire season.The number of firespots was gradually increased with the decrease of precipitation anomaly.Fire easily occurred in areas with temperature between 1 and 3?and precipitation anomaly between-1 and 1mm;Fire easily occurred in plat areas,the areas with elevation between 80 and 700m,slope between 0°and 7°and relief amplitude between 1 and 70m.It was found that the number of hotspots increased at first and then decreased with the rise of elevation,while decreased with the increase of slope and relief amplitude.No significant differences were observed in the indicator?number of firespots?studied among different aspects;When the distance from the residential area was less than 10km,the number of fire increased with the increase of distance,but when the distance from the residential area was more than 10km,the number of fires showed a decreasing trend as the distance increased.As the distance from the road increased,the number of fire points tend to decrease.When the distance from the road was less than 5km,a total of 8,403 firespots was found,accounting for 69.9%of the total number of firespots.?4?There was an obvious regional difference in the distribution of fire risk zones in Inner Mongolia,being higher in northeast,lower in southwest.The fire risk map was divided into four classes:high,medium,low and extremely low based on natural break method.The high risk areas of the fire were mainly concentrated in the western foothills of Daxinganling Mountains,the western margin of Songnen Plain,eastern part of Xilin Gol prairie,the West Liaohe plain and the Hetao-Tumochuan plain.The middle risk areas were located in the Daxinganling forest area and the southeastern part of the Hulunbeier grassland.The low-risk areas were mainly distributed in two areas:?1?the northern edge of Ergun and Genhe;?2?the majority area of Abag Banner and the area extends southwestwards from Zhenglan Banner to Guyang County.The extremely low risk areas of the fire were mainly distributed in areas extends southwestwards from Sunite Banner to Wulate Banner and Dengkou County and the whole area of Alashan.In order to verify the results of risk assessment and zoning in this study,the proportion of firespots and burned areas in four fire risk levels were calculated.More than 90%of burned areas and firespots were located in high risk areas and medium risk areas which showed that fire risk assessment model had good accuracy.Considering the natural attributes of fire,this paper implemented a fire risk assessment based on grid criterion.Compared with the current fire risk map in Inner Mongolia,the spatial variation of fire risk was no longer restricted by administrative units.Through the above analysis,we could deepen our understanding of the fire occurrence and fire risk changes in Inner Mongolia to some extent.It also could provide scientific basis for fire monitoring,risk assessment and early warning,and the formulation of the strategy of fire risk management. |
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