| Global warming is an indisputable fact resulting in a series of environmental problems.Governments,researchers and the public have been widely concerning those kinds of problems.Drought is a natural phenomenon,which describes a period of below-average precipitation,causing a prolonged shortage in the water supply.It is one of the world's severely natural disasters,and it is an important aspect of the impact of climate change.The highly frequent and increasing intensity droughts have been bringing significant negative impacts on our daily life and the product of industry and agriculture in a warming world.Located in the northern border of China,Inner Mongolia autonomous region,one of the four great grasslands in China,is a crucial ecological barrier.Meanwhile,it is very sensitive to global warming.People mainly rely on grassland animal husbandry and agriculture in there,but they are vulnerable to natural disasters,especially drought.Due to the global warming,this region is prone to frequent droughts.It is of great significance to analyze the climate changes in its historical state and predict it under different scenarios.As a drought monitoring index,the standardized precipitation evapotranspiration index(SPEI)was used to research the meteorological drought over Inner Mongolia in this research.Based on meteorological data,vegetation remote sensing data and climate model data,the spatial-temporal variation characteristics of temperature,precipitation and climate extremes from 1960 to 2015 were fully analyzed firstly.Secondly,the frequency,range,and intensity of drought,the trends and change-points of drought in different time scales were analyzed,and then their impact factors were discussed.Finally,drought variations in 2016-2100 under the Representative Concentration Pathway(RCP)2.6,RCP4.5 and RCP8.5 emission scenarios were estimated.This work led to the following main conclusions:(1)The annual average temperature was increasing significantly with a rate at 0.36?/10 a,and the change-point is in 1989.The temperature increaseed in four seasons,especially in winter.Spatially,the rate of temperature increase in the west was higher than that in the east.The inter-annual fluctuation of precipitation is large and shows a decreasing trend.The precipitation increased mainly in the northeast and west.The annual average potential evapotranspiration also showed a decreasing trend.The evaporation in the eastern part of the study area showed an increasing trend,while that in the central and western regions showed a decreasing trend.(2)Low-temperature extremes showed a significant downward trend,while high-temperature extremes showed a significant upward trend,and the temperature increase at night was greater than that in the day.Spatially,both the declining and rising trend of low-temperature extremes and high-temperature extremes gradually increased from the east to the west.Although the changes in precipitation extremes were not obvious,it increased in the northeast but decreased in the central and western regions.(3)The SPEI presented a nonsignificant increase in the past 56 years,with abrupt changes in 1975 and 2001,gradually changing from drought to humid and then to drought.Spatially,drought alleviated in the west but intensified in the east.The frequency of drought in western Inner Mongolia is higher than that in eastern Inner Mongolia.From 2000 to 2015,drought shown the most extensive and highest intensity,followed by the 1960 s.(4)Precipitation extremes played a great role in changing SPEI,which was positively correlated with SPEI.Extreme low-temperature events were generally negatively correlated with SPEI,while the extreme high-temperature events were positively correlated with SPEI.The significant increase of extreme high temperature events in Inner Mongolia region promoted the occurrence of drought events.El Nino-Southern Oscillation(ENSO),Arctic Oscillation(AO)and Pacific Decadal Oscillation(PDO)had a strong positive correlation with SPEI in Inner Mongolia,with resonance periods at different time scales.During the study period,as the analysis of land-use shown that grassland and woodland in Inner Mongolia were mostly reduced and transformed into arable land and sandy land,resulting in sparse surface vegetation and more bare land,which can provide conditions for the occurrence of drought events due to this transformation increased the albedo of the surface.(5)From 1982 to 2015,Normalized Difference Vegetation Index(NDVI)in Inner Mongolia showed a slowly rising trend with a fluctuation rate of 0.003/10 a.In spring,the rising rate of NDVI was the highest and up to 0.006/10 a.In the past 34 years,the area of NDVI in Inner Mongolia showed a growing trend(69.47%),which was much higher than that in the degradation trend(30.53%).The areas with a significant increase in NDVI were mainly distributed in the desert grasslands and sandy vegetation zones in western Inner Mongolia.The vegetation in Inner Mongolia was greatly affected by drought in summer and autumn.In summer,it was affected by drought from west to east with the corresponding from 3-month drought to 12-month drought,while it was mainly affected by three-month scale drought in autumn.Different vegetation types were greatly affected by different-time-scale drought: the deciduous broad-leaved forest was least;desert steppe,desert vegetation,and shrub were mainly affected by 12-month drought;typical steppe and meadow steppe are mainly affected by 3-month and 6-month drought.(6)The annual and seasonal temperature in Inner Mongolia both have increased with the increase of the concentration of greenhouse gas(GHG)emissions,and the higher the concentration of GHG,the greater the temperature rise.The temperature in winter increases the most.Under three emissions scenarios,the average temperature rise rate in Inner Mongolia were 0.02?/10 a,0.24?/10 a,and 0.61?/10 a.In the spatial scale,there shown an increasing trend from west to east.Annual and seasonal precipitation both have increased with the increase of GHG emission concentration,and the higher the concentration of GHG,the greater the increase of precipitation also.Precipitation in summer increases the most,followed by spring.In terms of spatial variation,the increasing trend of precipitation in the eastern part was greater than that in the western part.(7)With the increase of GHG emission concentration,SPEI in Inner Mongolia decreased fiercely during 2016-2100,resulting in severe drought.In terms of its distribution,the decreasing trend gradually increased from the east to the west.Correspondingly,with the increase of greenhouse gas emission concentration,the frequency and grade of drought increased,and the frequency of drought in the western part was higher than that in the eastern part.Under the scenario of RCP8.5,the frequency of drought at the end of the 21 st century was more than 90%,and severe drought disaster may occur.Under the influence of drought,with the increase of greenhouse gas emission concentration,the rate of decreasing NDVI in Inner Mongolia will increase in the future.The area of NDVI reduction trend was larger than the area of NDVI increase trend,and the reduction trend of NDVI in the western part of the study area was larger than that in the eastern part.This study systematically analyzed the change characteristics of temperature and precipitation in Inner Mongolia in history and future,as well as the frequency,intensity and impact of drought.The results of the study will provide scientific basis for rational utilization of water resources,drought identification,risk assessment of drought disasters and formulation of disaster prevention and mitigation countermeasures,which is of great significance for regional sustainable development. |
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