An_overall_co..._in_1970–2018_LUO Dengnan.pdf

J.Geogr.Sci.2023,33(3):449-463 DOI:https:/doi.org/10.1007/s11442-023-2091-0 2023 Science Press Springer-Verlag An overall consistent increase of global aridity in 19702018 LUO Dengnan1,*HU Zhongmin2,3,DAI Licong2,HOU Guolong1,DI Kai1,LIANG Minqi1,CAO Ruochen4,ZENG Xiang1 1.School of Geography,South China Normal University,Guangzhou 510631,China;2.Key Laboratory of Agro-Forestry Environmental Processes and Ecological Regulation of Hainan Province,Hainan University,Haikou 570228,China;3.Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai 519082,Guangdong,China;4.International Institute for Earth System Sciences,Nanjing University,Nanjing 210023,China Abstract:Climate change is expected to introduce more water demand in the face of dimin-ishing water supplies,intensifying the degree of aridity observed in terrestrial ecosystems in the 21st century.This study investigated spatiotemporal variability within global aridity index(AI)values from 19702018.The results revealed an overall drying trend(0.0016 yr-1,p0.01),with humid and semi-humid regions experiencing more significant drying than other regions,including those classified as arid or semi-arid.In addition,the Qinghai-Tibet Plateau has gotten wetter,largely due to the increases in precipitation(PPT)observed in that region.Global drying is driven primarily by decreasing and increasing PPT and potential evapotran-spiration(PET),respectively.Decreases in PPT alone or increases in PET also drive global aridification,though to a lesser extent.PPT and increasing potential evapotranspiration(PET),with increasing PET alone or decreasing PPT alone.Slightly less than half of the worlds land area has exhibited a wetting trend,largely owing to increases in regional PPT.In some parts of the world,the combined effects of increased PPT and decreased PET drives wetting,with decreases in PET alone explaining wetting in others.These results indicate that,without consideration of other factors(e.g.,CO2 fertilization),aridity may continue to intensify,espe-cially in humid regions.Keywords:aridity index;climate change;arid area;drying trend 1 Introduction Increasing aridity,a manifestation of climate change,is a serious threat to ecosystems(Huang et al.,2016b;Zhao et al.,2020;Hu et al.,2022).Declining rainfall has resulted in Received:2022-02-21 Accepted:2022-09-06 Foundation:National Natural Science Foundation of China,No.31922053;The Second Tibetan Plateau Scientific Expedi-tion and Research Program,No.2019QZKK0405;The Hainan University Start-up Fund,No.KYQD(ZR)21096;The Key R&D Program of Hainan,No.ZDYF2022SHFZ042 Author:Luo Dengnan(1997),MS,specialized in extreme events and terrestrial ecosystem carbon cycle.E-mail:.*Corresponding author:Hu Zhongmin,Professor,E-mail: 450 Journal of Geographical Sciences the expansion of the area classified as arid or semi-arid(Dai,2012;Sheffield et al.,2012;Huang et al.,2016a),and the frequency and intensity of droughts are projected to increase as global change continues(Strzepek et al.,2010;Asadi Zarch et al.,2015).This expansion of aridity is the result of an imbalance between water supply and demand.Empirically based models predict that the intensity and duration of drought will increase due to the increase in potential evaporation rate driven by rising temperatures and regional decreases in precipita-tion(Dai,2012).This will make the impacted terrestrial ecosystems more vulnerable and sensitive to climate change(Lian et al.,2021;Zeng et al.,2022).In order to understand how terrestrial ecosystems may change in response to climate change,it is crucial to assess vari-ability in dryness across the biosphere and the factors driving it.An aridity index(AI)is a widely used metric that quantifies aridity.Scientists have de-veloped various AIs based on meteorological factors such as temperature,precipitation,and potential evapotranspiration(PET)(Necula et al.,1998;Arora,2002;Li et al.,2019).The AI proposed by the Food and Agriculture Organization(FAO)of the United Nations is defined as the ratio of precipitation to PET(Allen et al.,1998).It is clear,simple,and practical to use and is effectively used in assessments of aridity(Greve et al.,2019;Zhou et al.,2020).Many studies have used the FAO AI to assess aridity in different regions.For example,Huang et al.(2016b)found that the expansion of drylands occurs mainly in semi-arid re-gions around the world due to decreasing values of AI in these regions.Mu et al.(2013)found that the Asia-Pacific region experienced more frequent and intense drought events from 2000 to 2011.Dryness in Iraq increased significantly from 1980 to 2011,with drought severity increasing since 1997 owing to a reduction in precipitation and an increase in tem-perature(arlak and Mahmood Agha,2018).Although a few studies have reported interan-nual variability in the aridity of humid regions(Ullah et al.,2022),most have focused either on drylands(Mu et al.,2013;Asadi Zarch et al.,2015;Huang et al.,2016a;Pan