Climate and Water Cycle, Ecology

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  • 1  Interdecadal variation of land water budget in Northwest China from 1961 to 2016
    WANG Aihui MIAO Yue CHEN Yue
    2020, 43(6):953-966. DOI: 10.13878/j.cnki.dqkxxb.20201112001
    [Abstract](840) [HTML](779) [PDF 16.47 M](2293)
    In recent decades,the "warming and wetting" in Northwest China has become the consensus of the scientific community,and much research has been conducted regarding water and heat transport between land and atmosphere.Station observations show that the annual precipitation has been increasing since the early 1980s under the land surface warming background.As a notable arid-semiarid regions,the social and economic developments in Northwest China is strongly dependent on water resources.The land water availability (LWA),which is the residual of precipitation and evaporation,typically denotes natural water resources.However,the long-term characteristics and decadal variability of LWA in Northwest China are not clear,due to the lack of a reliable and long-term evaporation dataset.In our previous work,a long-term 0.25 deg daily land surface hydrological and fluxes dataset (referred as to VIC-CN05.1) was developed,and has provided a high quality evaporation dataset for exploring LWA variability.In the present study,we analyze the long-term and decadal characteristics of the land water budget in the northwestern region during the 1961-2016 warm season (May-September).The station observational meteorology dataset (CN05.1) VIC-CN05.1 and atmospheric reanalysis (JRA55) are used.The Mann-Kendal mutation test is adopted to test the LWA time series,and two abrupt change points in 1979 and 2008 are detected.Next,the studied period is divided into three sub-periods (P1:1961-1978;P2:1979-2008;P3:2009-2016) for further analysis.The main conclusions of the study are as follows:From 1961 to 2016,the LWA in the Northwest China warm season shows an upward tendency.The regional mean LWA time series exhibits obvious decadal characteristics,and the LWA anomaly percentage in the three periods are -5.45%,-0.46% and 13.99%,respectively,showing a general characteristic of "decreasing-invariable-increasing".The spatial distributions of the LWA change are significantly different in the three periods,particularly in central Xinjiang,eastern Gansu and Shaanxi Provinces.Sufficient water vapor and rising motion are the necessary conditions for precipitation,and the atmospheric circulation has a major influence on precipitation change in Northwest China.The changes in water vapor flux transport and vertical velocity in Northwest China are basically consistent with the decadal variation characteristics of precipitation overall,with obvious regional difference distribution characteristics.Evaporation in Northwest China is closely related to near-surface meteorological elements,and is mainly affected by precipitation,downward longwave radiation and wind speed.It should be noted that we treat the Northwest China region as a whole,although this region exhibits a high degree of LWA spatially heterogeneity.In the future,it is necessary to analyze the LWA change in different sub-regions.Moreover,the effects of land use change and human activities on water resources must also be considered.
    2  Climate change in the upper Yellow River Basin and its impact on ecological vegetation and runoff from 1980 to 2018
    YE Peilong ZHANG Qiang WANG Ying XU Lili HAN Linjun LI Rong
    2020, 43(6):967-979. DOI: 10.13878/j.cnki.dqkxxb.20200924001
    [Abstract](1403) [HTML](1012) [PDF 22.70 M](2455)
    The upper Yellow River Basin is the most important water conservation and runoff producing areas in the Yellow River Basin,which is of decisive significance to the water resources security,ecological environment and food security of the Yellow River Basin.In recent years,under the background of warm and humid climate in Northwest China,the climate,ecology,hydrology and other issues in the upper Yellow River Basin have attracted great attention.Based on satellite remote sensing data,grid fusion data and hydrological monitoring data,this paper analyzes the multi-scale variation characteristics of climate and its impact on ecological vegetation and runoff in the upper Yellow River Basin.Results are summarized as follows:(1) From 1980 to 2018,the warming and wetting trend in the upper Yellow River Basin presents a relatively consistent climate characteristics in the whole region.The temperature and precipitation increase rates are 0.023℃/a,1.09 mm/a respectively.However,there are obvious regional differences at the same time.The increasing trend of precipitation is the most obvious over the confluence area of Huangshui River Basin and central part of Gansu Province,and the increasing trend of temperature is the most obvious in the desert area of Ningxia and Nei Monggol.Since 2000,the precipitation in the whole upper Yellow River Basin has increased significantly.After 2000,the actual evapotranspiration increases significantly in the confluence and flow areas but decreases in the south of the source area.(2) The current warm and humid climate is conducive to vegetation growth in the upper Yellow River Basin,and the vegetation growth rate has reached 0.04/(10 a) in the confluence and source areas since 1999.From the long-term trend,the vegetation index in the source and confluence areas has a significant positive correlation with precipitation in the previous year,while the vegetation index in the flow area has a significant correlation with precipitation in the current year.Precipitation has obvious effect on vegetation improvement in the upper Yellow River Basin,while temperature has more complex effect on vegetation.Different vegetation types in different regions are the possible reasons for the differences of precipitation,temperature and evapotranspiration.(3) Affected by the climate and vegetation variations,the annual runoff of Tangnaihai and Lanzhou stations shows a decreasing trend from 1980 to 2018 but a significant increasing trend since 1998,and the increase rate of annual runoff of Lanzhou station is three times that of Tangnaihai station.The long-term trend shows that annual runoff has a significant positive correlation with precipitation at Tangnaihai station in the current year,and the correlation coefficients of annual runoff with annual precipitation and evapotranspiration at Lanzhou station in the current year are significantly lower than those at Tangnaihai station.From the perspective of interannual fluctuation (after detrend),precipitation is the most important factor determining annual runoff,and the influences of ecological vegetation,frozen soil degradation,water storage change and social activities on runoff should not be ignored.This study provides a reference for scientific response to ecological protection in the upper Yellow River Basin and the realization of high-quality development of the Yellow River Basin.
    3  Changes in climate,glaciers and permafrost during 1979-2018 in Tibetan Autonomous Region and their potential impacts on renewable energy
    ZOU Mijun SHAO Changkun YANG Kun
    2020, 43(6):980-991. DOI: 10.13878/j.cnki.dqkxxb.20201010010
    [Abstract](787) [HTML](673) [PDF 38.55 M](2253)
    Tibet is rich in renewable energy,while also being highly ecologically fragile and sensitive to climate change.In this study,the changes in climate,glaciers and permafrost in Tibetan Autonomous Region during the past 40 years (1979-2018) and their potential impacts on renewable energy were analyzed based on multi-source data.The results show the following:1) During 1979-2018,northern Tibet has become warmer and wetter while southern Tibet has become warmer and drier.The air temperature has increased at an average rate of 0.54℃·(10 a)-1.In addition,the precipitation has increased in northern Tibet,while having slightly decreased in the south.2) The sunshine durations,as well as the wind speed,showed significant decreases.However,the wind speed ceased declining around 2002,and rose again after 2010.3) The glaciers retreated rapidly,especially in southeastern Tibet and the Nyainqentanglha region,with the maximum thinning rate exceeding 8.0 m·(10 a)-1.Permafrost covers approximately 43% of Tibet,with weak stability and strong degradation.In summary,solar and wind energy have decreased in Tibet in the past 40 years.Hydropower has increased due to glacier retreating and permafrost degradation,yet its accurate prediction remains a challenge.
    4  Simulated response of warming to Southeast Asian deforestation: insights from WRF simulations using three land surface models
    WANG Dashan WU Jie JIANG Xin LIANG Shijing ZENG Zhenzhong
    2020, 43(6):992-1001. DOI: 10.13878/j.cnki.dqkxxb.20200927001
    [Abstract](1013) [HTML](879) [PDF 44.18 M](2920)
    Tropical forest has undergone rapid loss in the early 21st century,leading to warming effects on regional climate,mainly by means of changing evapotranspiration.Regional climate models are powerful tools for assessing the biophysical feedbacks of deforestation.As the key part of climate models,land surface schemes regulate the fluxes of heat and water vapour between land and atmosphere,which may greatly affect the pattern and magnitude of how changes in forest cover impact climate.In this study we investigate the deforestation-induced warming effect in the Southeast Asian Massif by employing three land surface schemes (NoahMP,CLM and Noah mosaic) in the Weather Research and Forecasting (WRF) model.We perform the analyses by designing two sets of experiments with comparative land-cover scenarios,derived from high-resolution forest cover change dataset during the local dry season.Model validations show that,regarding the magnitude,the CLM scheme is in good agreement with the observed surface air temperature,while the Noah mosaic scheme has the greatest negative biases.When comparing the results between the two scenarios,it is found that only the Noah mosaic scheme,which takes the sub-grid approach,reasonably reproduces the response of warming effect to deforestation.In contrast,the NoahMP scheme fails to accurately capture the deforestation-induced regional warming,due to the use of the dominant approach at grid level.The CLM,a scheme which theoretically considers all land cover types within girds,and thus should possess the capability to capture the climate feedbacks of deforestation,is less sensitive to forest loss in those grids where the dominant type remains unchanged,and presents a pattern of temperature change similar to that of the NoahMP scheme.Based on these results,we speculate that the CLM scheme takes the dominant approach instead of the all-type mosaic method when coupled into the WRF model.This work demonstrates that the Noah mosaic scheme could be temporally applied in simulating the climate feedbacks of land cover conversion.We suggest that the representations of sub-grid characteristics in the CLM scheme be modified in the next version of the WRF model.
    5  Research progress on moisture source change of precipitation over the Tibetan Plateau and its surrounding areas
    TANG Qiuhong LIU Yubo ZHANG Chi SU Fengge LI Ying GAO Yanhong LI Wenhong CHEN Deliang
    2020, 43(6):1002-1009. DOI: 10.13878/j.cnki.dqkxxb.20201003001
    [Abstract](1390) [HTML](1800) [PDF 2.89 M](2110)
    This paper provides a comprehensive review of recent studies on the moisture sources of precipitation over the Tibetan Plateau and its surrounding areas,focusing on the characteristics of moisture sources(regions of evaporation) for precipitation,the spatiotemporal changes in contribution of moisture sources to precipitation,and the causes of changes in moisture source associated with wetting trend over the Tibetan Plateau and drying trend in Southwest China(located in the southeastern margin of the Tibetan Plateau).The existing studies show that the moisture transports from the west of the Tibetan Plateau by mid-latitude westerlies in the Northern Hemispheric and from the southwest by the Indian summer monsoon contribute the most to precipitation over the Tibetan Plateau.The moisture transports from the west show an overall decreasing trend while those from the south and the east show an overall increasing trend in the past three decades.The enhanced water vapor transport from the monsoon regions and the intensified local hydrological recycling are the primary reasons behind the recent wetting trend over the Tibetan Plateau,while the reduced water vapor transport from the regions dominated by the westerlies is the main factor that causes the drying trend in the southeastern margin of the Tibetan Plateau.This paper discusses the challenges and future directions for understanding the variation of moisture source of precipitation over the extended Tibetan Plateau area.Firstly,the observational evidence of moisture source variation is still lacking.There is a need to reduce uncertainty of the moisture source estimates through integration of model and observations.Secondly,the changes in glacier,lake and vegetation over the Tibetan Plateau and the associated changes in evapotranspiration would affect the water vapor transport and recycling.There is a need to quantify the interactions between land surface change and precipitation over the Tibetan Plateau and its surrounding areas from the perspective of water vapor sources.Thirdly,the enhanced moisture supply from the monsoons and reduced moisture supply from the westerlies could be linked to climate change as the projection of future precipitation changes under a warming world shows the same pattern as the past three decades,i.e.a wetting trend over the Tibetan Plateau and a drying trend in the southeastern margin.However,further researches are needed to understand the linkages between global change and moisture source variation over the Tibetan Plateau and its surrounding areas.
    6  Simulations of the water balance components of the sub-regions in the Lancang-Mekong River Basin in the context of global climate change
    WANG Guoqing QIAO Cuiping WANG Jie LAN Yunlong TANG Xiongpeng
    2020, 43(6):1010-1017. DOI: 10.13878/j.cnki.dqkxxb.20200921010
    [Abstract](723) [HTML](760) [PDF 3.22 M](1923)
    Catchment hydrological models are of vital importance in regional water resource assessments.In this study,based on the Princeton Meteorological Forcing Dataset and the recorded runoff data at eight hydrometric stations on the Lancang-Mekong River,the hydrological characteristics of the eight sub-regions were analyzed.The regional runoffs,as well as other key water balance components,were successfully simulated using an RCCC-WBM model.The obtained results revealed that the Lancang-Mekong River Basin was characterized by high differences in hydro-meteorological features.For example,the temperature levels in the upper reaches were much lower.However,those areas displayed larger ranges of seasonal variations.Meanwhile,the temperature levels in the middle and lower reaches were higher,with narrow variation ranges in seasonal temperatures.In addition,the seasonal patterns of the runoff were generally consistent with that of the precipitation,with one-month lags in runoff peaks occurring.This study's RCCC-WBM model was able to effectively simulate the monthly runoff patterns for the sub-regions of the Lancang-Mekong River Basin,with Nash-Sutcliffe coefficients over 60% in both the calibration and validation periods.The model achieved a relative error of runoff volume varying in a range of ±10%,which indicated the suitability of the model for studying catchments.The seasonal patterns of the simulated soil moisture were found to be characterized by first decreasing trends and then increasing trends,followed with decreases again due to influencing effects of seasonal variations in precipitation and evaporation.The main water sources for the runoff yields and the actual evaporation consumption values were observed to change with the different seasons.It was determined in this study that precipitation was the main source of the runoff yields and evaporation during the flooding seasons,while soil moisture played an important role in providing resources for both consumption processes during the dryer seasons.
    7  Analyses of flash-flood response characteristics using long-term rainfall-runoff observational data: a case study of two small watersheds in the United States
    HU Ying WU Huan Xu Hui ZHENG Jing ZHOU Naijun HUANG Zhijun CHEN Weitian LI Chaoqun
    2020, 43(6):1018-1030. DOI: 10.13878/j.cnki.dqkxxb.20201010001
    [Abstract](742) [HTML](679) [PDF 20.46 M](1980)
    This research investigation constructeda unit hydrograph(UH) for the purpose of simulating flash floods in small catchments using long-term rainfall-runoff data.The characteristics of the flash-flood responses were described,particularly from the aspect ofprecipitation.In addition,this study explored how the characteristics of flash-flood responses changed under different environmental conditions.Two small catchments (USGS gauges at the Catawba River and Swatara River) in the United States were investigated in this study.It was found that when the antecedent precipitation indexes (API) were high,the peak UH valueswere higher and the peak current timeshad occurred earlier.The results of the surface runoff simulations using the average UH with different API were considered to be promising,with average Nash efficiency coefficients of 0.846 and 0.940,respectively.The average relative peak errors were determined to be 9.40% and 7.47%,respectively.It was observed that by combining the rainfall and flood-causing precipitation values,the simulation results could be further improved and better represent the characteristics of flash-flood responses.Generally speaking,the method used in this study was considered to have very good potential for real-time flash-flood forecasting processes.Furthermore,further analyses of the interannual variations of UH in the CatawbaRiver Basin indicated intensified flash-flood responses with increasing peak magnitudes and decreasing flood durations.These findingswere found to correspondwell with the increases in both accumulated precipitation amounts and frequency of heavy rainfall observed during the past several years in the study area.
    8  Study on the seasonal different characteristics of streamflow and climate factors in the Lancang-Mekong River Basin
    LIU Songnan WANG Jun
    2020, 43(6):1031-1041. DOI: 10.13878/j.cnki.dqkxxb.20201031001
    [Abstract](798) [HTML](764) [PDF 2.61 M](1894)
    In this study,based on DELWARE temperature and precipitation data,GLDAS evapotranspiration data,and measured streamflow from nine hydrological stations located along the mainstream of the Mekong River,the regression analysis,T test and low-pass filter were used to analyze the climate and streamflow changes in the basin during the periods of 1950-2017.The results show that the average temperature of the basin is increasing,and since 2008,the temperature has increased significantly,while the average precipitation in the basin has changed little.The average evapotranspiration in the basin shows a decreasing trend in December-January,and an increasing trend in other months.The average evapotranspiration in 2008-2017 has increased significantly compared with the average evapotranspiration in 1950-2007(June-October).The annual streamflow in the basin has not changed significantly,but since 2008 the streamflow shows an increasing trend in December-April,along with a decreasing trend in July-October.The increasing trend is more obvious than the decreasing trend,and the increasing trend in January-April is more significant after 2008.For the yearly minimum streamflow,there is a significant increasing trend after 2008,and the maximum streamflow shows a decreasing trend after 2008.The streamflow reversals have increased significantly since 1990.By comparing temperature,precipitation,evapotranspiration and streamflow changes in different time periods,it can be seen that the change of streamflow after 2008 is not significantly related to the changes of natural climate,but may be significantly related to the dams' water storage capacities (human activities).
    9  Changes of climate and climate extremes in the Three-Rivers Headwaters' Region over the Tibetan Plateau during the past 60 years
    JIN Zheng YOU Qinglong WU Fangying SUN Bo CAI Ziyi
    2020, 43(6):1042-1055. DOI: 10.13878/j.cnki.dqkxxb.20201008001
    [Abstract](1102) [HTML](974) [PDF 54.99 M](2087)
    The Three Rivers Headwaters' Region is significant and sensitive to climate change,which is characterized with "warmth and wetness".From such perspectives as spatial pattern,climate extreme indices and comparison among regional-global climate variations,characteristics of climate variations and climate extremes in the Three Rivers' Headwaters Region over the Tibetan Plateau from 1961 to 2019 was studied.Temperature and precipitation observation data were obtained from 20 meteorological stations of China Meteorological Administration,HadCRUT4 as well as NOAA Precipitation Reconstruction datasets.It was revealed that the spatial averaged warming rate was 0.37℃/(10 a),which was more than the global average level (0.16℃/(10 a)) during the past 60 years and was also significantly higher than that in the same latitude (0.19℃/(10 a)) and in China (0.28℃/(10 a)).Under the background of global warming,most of the extreme climate indices in the Three Rivers' Headwaters Region have risen,and the most significant one is night extreme high temperature (0.55℃/(10 a)),suggesting the extremeness of regional climate has strengthened.The spatial pattern of temperature and precipitation during the past 60 years shows a positive gradient along the northwest-southeast direction,and its variation is characterized by a rising trend in the spatial differentiation of warming and humidification from west to east.Furthermore,the temporal-spatial patterns of climate change and climate extremes in the Three Rivers' Headwaters Region can provide some bases for research on the vulnerability of climate systems and ecosystems in this region.At the same time,this study also provides a comparative case for studies on the response of climate-sensitive alpine regions to global warming.
    10  Risk estimation of extreme high temperature in eastern China under 1.5 and 2℃ global warming
    JIANG Xiaofei JIANG Zhihong LI Wei
    2020, 43(6):1056-1064. DOI: 10.13878/j.cnki.dqkxxb.20201011001
    [Abstract](319) [HTML](578) [PDF 13.26 M](2106)
    In 2013,a record-breaking extreme high temperature occurred in central and eastern China,causing serious losses to social economy and property of people.Based on the daily maximum temperature from CN05.1 and the data from 17 CMIP5 models,this paper studies the risk of the record-breaking extreme high temperature in 2013 and the extreme high temperature with long return periodsof 20,50 and 100 years under the global warming of 1.5 and 2℃ in the future.The daily maximum temperature data simulated by CMIP5 models are corrected by the bias-corrected method of quantile mapping.Results show that the bias correction can significantly reduce the biases of simulated maximum temperature.Compared with the historical period from 1986 to 2005,the risk of occurrence of extreme high temperature intensity (days)in 2013 will increase to 3.0/6.1 (5.6/12.6) time sunder the global warming of 1.5/2℃ in the future.From 1.5℃ to 2℃,the additional 0.5℃ warming will increase the future risk of extreme high temperature intensity (days) in 2013 to 2.0 (2.3) times.For extreme high temperatures with different return periods,the rarer high temperatures have larger risk increase in the future,and the risk of increasing of extreme temperature days is greater than that of the intensity.The days of extreme high temperature that occurred once in 20,50 and 100 years in the historical period will become once in 4,8 and 15 years (once in 2,3 and 6 years) under the global warming of 1.5℃ (2℃) in the future.The intensity of extreme high temperature that occurred once in 20,50 and 100 years in the historical period will become once in 7,14 and 27 years (once in 4,6 and 8 years) under the global warming of 1.5℃(2℃) in the future.
    11  Vegetation cover change in the Indo-China Peninsula in spring and its relation to ENSO
    CHEN Haishan QIAN Manyi HUA Wenjian
    2020, 43(6):1065-1075. DOI: 10.13878/j.cnki.dqkxxb.20201014007
    [Abstract](337) [HTML](728) [PDF 22.05 M](2021)
    This paper investigates the characteristics of vegetation cover change in the Indo-China Peninsula and its relationship with ENSO(El Niño-Southern Oscillation) using the NDVI(Normalized Difference Vegetation Index),climate data and circulation field data.Results show that precipitation is the main factor of vegetation growth in spring and has a significant positive correlation with NDVI,while temperature and radiation have negative correlations with NDVI.Further analysis reveals that when sea surface temperature in the equatorial central and eastern Pacific in the preceding winter is warmer(El Niño event occurs),the sea level pressure is higher and the 850 hPa wind field is divergent near the Indo-China Peninsula,where the upward movement is weaker,which is not conducive to the formation of cloudiness and precipitation,but conducive to the increase of solar radiation and temperature.The reduced precipitation and higher temperature both inhibit the growth of vegetation in the Indo-China Peninsula in spring.On the contrary,La Niña event in the preceding winter is favorable for the vegetation growth in the Indo-China Peninsula.
    12  Trend and influencing factors of global river discharge in recent 60 years
    ZHOU Guoyi LI Lin FANG Xuechun HAN Shihui SHI Tingting
    2020, 43(6):1076-1085. DOI: 10.13878/j.cnki.dqkxxb.20201018001
    [Abstract](901) [HTML](839) [PDF 9.07 M](1607)
    Based on the background of rising temperature,changes in precipitation and its pattern,and increased vegetation coverage and biomass,the changes in global water resources have attracted widespread attention and concern.This paper analyzes the long-term data of river discharge,normalized differential vegetation index(NDVI),annual mean temperature and annual precipitation in 2 894 watersheds around the world.Results suggest that for the monthly mean discharge within the year(MQ),the proportion of watersheds with the trend of increasing,decreasing and not significantly changing is 9.1%,12.4% and 78.5% respectively;for the lowest monthly mean discharge(LQ),the corresponding proportion is 24.1%,11.7% and 64.2% respectively;and for the highest monthly mean discharge(HQ),the corresponding proportion is 6.4%,13.6% and 79.9% respectively.On regional(continent and latitude belts) and global scales,LQ decline and HQ rise are not found,MQ decline is associated with HQ decline,and MQ rise is associated with LQ rise,which indicates that the water resources quantity and annual distribution on regional and global scales have been improved in the past 60 years.Further analysis shows that climate change is the main factor leading to changes in water resources and annual distribution.However,different from the monthly extreme discharge(LQ or HQ) changes in a year,most of the months in which the monthly extreme discharge occurs have changed significantly.This change may have a profound impact on society and natural ecosystems,as well as production and lifestyle that rely on natural rhythms.
    13  A few thoughts on the study of flash drought
    YUAN Xing WANG Yumiao ZHANG Miao WANG Linying
    2020, 43(6):1086-1095. DOI: 10.13878/j.cnki.dqkxxb.20200914002
    [Abstract](844) [HTML](1679) [PDF 3.31 M](1906)
    Flash drought is a type of drought characterized by rapid intensification within a few weeks.It could be a "new normal" of drought in a warming climate,which needs further investigation.Regarding the debate on flash drought definition,this paper emphasizes the importance of understanding the difference and connection between flash drought and conventional drought,and clarifies flash drought in terms of rapid onset,duration,onset and recovery processes.This paper points out that the typical time scale of flash drought is sub-seasonal scale,which should be included in multi-scale drought system.This paper also overviews the progresses in extreme case diagnosis,detection and attribution of human activity,and ecological and environmental impact.Future focus could be the flash drought mechanism,including internal variability and external forcing,the interaction between flash drought and ecosystem,the identification of predictability sources of flash drought,and the development of prediction methods.It is encouraged to use research methods of earth system science and to develop advanced monitoring and modeling techniques for adapting to the increasing flash drought risk from a global change perspective.
    14  Impact of climate change on terrestrial water cycle in China
    SU Buda SUN Hemin LI Xiucang LI Zhenjie ZHANG Jingpeng WANG Yanjun HUANG Jinlong GAO Miaoni JIANG Tong SI Lili
    2020, 43(6):1096-1105. DOI: 10.13878/j.cnki.dqkxxb.20201014001
    [Abstract](280) [HTML](1291) [PDF 4.38 M](1721)
    Water cycle is one of the most active processes in the interaction among ocean,land and atmosphere,and affected significantly by climate change.This paper evaluates the changes of water cycle components including precipitation,evapotranspiration,surface runoff and water vapor in China and ten river basins since 1979 based on ground based observations and reanalyses.Results show that the atmospheric water vapor and water vapor budget have shown significant increase trends during 1979-2018 in China.But,a weak downward trend of atmospheric water vapor was found at the Songhua River Basin and the Southwest River Basin spatially.Except for the Northwest River Basin,where annual precipitation increased significantly,changes of precipitation in other river basins were not significant.Areal averaged annual actual evapotranspiration increased slightly in China,but decreased obviously at the most River basins in South China.As for surface runoff,a clear increase trend was detected at the Northwest River Basin,but negative trends were found at the majority of River basins in North China,while trends were complex at the River basins in South China.Relative to 1979-2000,annual mean temperature in China increased by about 0.63℃,and annual precipitation and atmospheric water vapor increased about 0.5% and 1.2%,respectively,in 2000-2018.Meanwhile,both inflow and outflow of water vapor decreased,and precipitation recycling ratio increased by 10.9%.Spatially,the internal water recirculation was more active than before in 2000-2018 at the most river basins escept for the Songhua and Liaohe River basins in Northeast China.Precipitation produced by local evapotranspiration and inflow water vapor were both increased at the Haihe,Yellow,Huaihe and Northwest River Basins.At the Songhua,Liaohe,Yangtze,Pearl and Southwest River Basins,increase of precipitation from local evapotranspiration was offset by more significant declining of precipitation from infow water vapor,and this effect was more obvious at the Liaohe River Basin than others.Precipitation produced by local evapotranspiration has increased slightly,but overall change of precipitation was not significant at the Southeast River Basin.
    15  Interannual variability of gross primary productivity at global FLUXNET sites and its driving factors
    YIN Xixi YUE Xu ZHOU Hao MA Yimian TIAN Chenguang CAO Yang LEI Yadong
    2020, 43(6):1106-1114. DOI: 10.13878/j.cnki.dqkxxb.20200913001
    [Abstract](1010) [HTML](1145) [PDF 5.86 M](1751)
    In this study,using the Yale Interactive Biosphere(YIBs) model,as well as the data from the FLUXNET sites with measurement records longer than 8 years,examines the impacts of multiple meteorological variables on the interannual variability of gross primary productivity(GPP),and identifies the dominant drivers of GPP variability for different plant functional types.The results showed that the change in photosynthetically active radiation is the main driving factor of GPP interannual variability for deciduous broadleaf forests and evergreen needleleaf forests,contributing 80% of the variability for these forest types.In addition,the change in relative humidity is the main driving factor of the GPP interannual variability for cropland,contributing 65% of its GPP variability.Temperature is an important factor for shrubland,its contribution rate is 58%.The GPP interannual variability of grassland shows great uncertainties among sites without uniform driving factors.Our results reveal that meteorological variables are the dominant drivers for the interannual variability of global terrestrial GPP.With the progression of future climate change,more frequent climate extremes may further increase the GPP interannual variability.
    16  Projected evapotranspiration and the influencing factors in the Yangtze River Basin based on CMIP6 models
    ZHAN Mingyue WANG Guojie LU Jiao CHEN Liqin ZHU Chenxia JIANG Tong WANG Yanjun
    2020, 43(6):1115-1126. DOI: 10.13878/j.cnki.dqkxxb.20200927002
    [Abstract](856) [HTML](1139) [PDF 32.25 M](2089)
    Evapotranspiration (ET) is the bridge among hydrologic and energy cycles,linking soil,vegetation and atmospheric processes.In this paper,based on the output of 12 CMIP6 (Coupled Model Intercomparison Project,phase 6) models,the actual ET change during 2020-2099 and the influencing factors in the Yangtze River basin are studied under SSP1-2.6,SSP2-4.5 and SSP5-8.5 climate change scenarios.The results show that the land ET has significantly increased under the three scenarios compared with the baseline period (1995-2015),particularly in the middle and lower reaches of the Yangtze River Basin.Under the SSP1-2.6 scenario,the ET increases rapidly until the 2060s,and then levels off,after which a continuous increase is indicated under both SSP2-4.5 and SSP5-8.5 scenarios.The influencing factors of precipitation (Pr),air temperature (T) and leaf area index (LAI) are studied,and T appears to be the most important factor influencing Yangtze ET under SSP1-2.6 and SSP2-4.5 scenarios;however,the LAI becomes dominant across the Yangtze River Basin under the SSP5-8.5 scenario.Under the three scenarios,the LAI increases significantly with increased radiative forcing,leading to significantly increased vegetation impact on land ET (SSP5-8.5 > SSP2-4.5 > SSP1-2.6);however,the sensitivity of ET to LAI change appears to decrease with increased radiative forcing (SSP1-2.6 > SSP2-4.5 > SSP5-8.5).

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