Variation of water body in Dongting Lake from in situ measurements and MODIS observations in recent decades

Identifying the spatiotemporal dynamics of the water body in Dongting Lake,the second largest freshwater lake in China,is crucial for water resource management.In this study,the variations of the water body were comprehensively analyzed based on remote sensing images and in situ measurements from 2000 to 2019.Four breakpoint detection approaches were integrated to analyze the change trends and explore the related driving forces behind the changes.The results showed that significant intra-and inter-annual fluctuations of the water body were found from 2000 to 2019.The water area and volume decreased at rates of 1.26 km^(2)/a and 16.65×10^(6)m^(3)/a,respectively.During the entire study period,the outflow at Chenglingji station(CLJ),the inflow from three outlets of the Yangtze River(Inflow2),and the inundation conditions during the last period(Arealag)made the largest relative contributions to the water area variation(around 25%,27%and 24%,respectively).A breakpoint was detected around 2004,corresponding to the operation period of the Three Gorges Dam(TGD).The regulation of TGD profoundly affected the hydrological characteristics at the three outlets and CLJ,and may have indirectly caused the water area to expand by 2.41 km^(2)/a during the dry seasons between 2004 and 2019.These results provide valuable insight into how natural and anthropogenic factors affect water body variation and may offer a practical reference for the local government to adjust management strategies.

Assessment of the high-resolution estimations of global and diffuse solar radiation using WRF-Solar

Compared with physical models,WRF-Solar,as an excellent numerical forecasting model,includes abundant novel cloud physical and dynamical processes,which enablesenable the high-frequency output of radiation components which are urgently needed by the solar energy industry.However,the popularisation of WRF-Solar in a wide range of applications,such as the estimation of diffuse radiation,suffers from unpredictable influences of cloud and aerosol optical property parameters.This study assessed the accuracy of the improved numerical weather prediction(WRF-Solar)model in simulating global and diffuse radiation.Aerosol optical properties at 550 nm,which were provided by a moderate resolution imaging spectroradiometer,were used as input to analyse the differences in accuracies obtained by the model with/without aerosol input.The sensitivity of WRF-Solar to aerosol and cloud optical properties and solar zenith angle(SZA)was analysed.The results show the superiority of WRF-Solar to WRF-Dudhia in terms of their root mean square error(RMSE)and mean absolute error(MAE).The coefficients of determination between WRF-Solar and WRF-Dudhia revealed no statistically significant difference,with values greater than 0.9 for the parent and nested domains.In addition,the relative RMSE(RRMSE%)reached 46.60%.The experiment on WRF-Solar and WRF-Dudhia revealed a negative bias for global radiation,but WRF-Solar attained a slightly lower RMSE and higher correlation coefficient than WRF-Dudhia.The WRF-Solar-simulated results on diffuse radiation under clear sky conditions were slightly poorer,with RMSE,RRMSE,mean percentage error and MAE of 181.93 W m^(−2),170.52%,93.04%and 138 W m^(−2),respectively.Based on Himawari-8 cloud data,statistical results on cloud optical thickness(COT)for cloudy days revealed that WRF-Solar overestimated diffuse radiation at COTs greater than 20.Moreover,when the aerosol optical depth was greater than or equal to 0.8,WRF-Solar also overestimated the diffuse radiation,with a mean difference of 58.57 W m^(−2).The errors of WRF-Solar simulations in global and diffuse radiation exhibited a significant dependence on the SZA.The dispersion degree of deviation increased gradually with the decrease in the SZA.Thus,WRF-Solar serves as an improved numerical tool that can provide high temporal and high-spatial-resolution solar radiation data for the prediction of photovoltaic power.Studies should explore the improvement of cumulus parameterisation schemes to enhance the accuracy of solar radiation component estimation and prediction under cloudy conditions.

Global DEMs vary from one to another:an evaluation of newly released Copernicus,NASA and AW3D30 DEM on selected terrains of China using ICESat-2 altimetry data

A good understanding of the quality of digital elevation model(DEM)is a perquisite for various applications.This study investigates the accuracy of three most recently released 1-arcsec global DEMs(GDEMs,Copernicus,NASA and AW3D30)in five selected terrains of China,using more than 240,000 high-quality ICESat-2(Ice,Cloud and land Elevation Satellite)ALT08 points.The results indicate the three GDEMs have similar overall vertical accuracy,with RMSE of 6.73(Copernicus),6.59(NASA)and 6.63 m(AW3D30).While the accuracy varies considerably over study areas and among GDEMs.The results show a clear correlation between the accuracy and terrain slopes,and some relationship between the accuracy and land covers.Our analysis reveals the land cover exerts a greater impact on the accuracy than that of the terrain slope for the study area.Visual inspections of terrain representation indicate Copernicus DEM exhibits the greatest detail of terrain,followed by AW3D30,and then by NASADEM.This study has demonstrated that ICESat-2 altimetry offers an important tool for DEM assessment.The findings provide a timely and comprehensive understanding of the quality of newly released GDEMs,which are informative for the selection of suitable DEMs,and for the improvement of GDEM in future studies.

Evaluation of satellite land surface albedo products over China using ground-measurements

Land surface albedo(LSA)is an important parameter in surface energy balance and global climate change.It has been used in the fields of energy budgets,climate dynamics,and land surface processes.To apply satellite LSA products more widely,the product accuracy needs to be evaluated at different scales and under atmospheric and surface conditions.This study validates and analyzes the errors of the LSA datasets from the Global LAnd Surface Satellites(GLASS)product,the European Space Agency’s Earth Observation Envelope Programme(GlobAlbedo),the Quality Assurance for Essential Climate Variables(QA4ECV)project,the Gap-filled Snow-free Bidirectional Reflectance Distribution Function(BRDF)parameters product(MCD43GF),and the Satellite Application Facility on Climate Monitoring(CM SAF)Albedo dataset from the AVHRR data(CLARA-SAL)against the Chinese Ecosystem Research Network(CERN)measurements at different spatiotemporal scales over China from 2005 to 2015.The results show that LSA estimated by GLASS agrees well with the CERN measurements on a continental scale.The GLASS product is characterized by a correlation coefficient of 0.80,a root-mean-square error of 0.09,and a mean absolute error of 0.06.The consistency between GLASS,GlobAlbedo,and CLARA-SAL is slightly lower over the regions with high aerosol optical depth(AOD)(e.g.Sichuan Basin,northern China)and high cloud cover compared with that in regions with lower AOD and low cloud cover.The estimation errors are related to varying atmospheric and surface conditions and increase with increasing AOD and cloud cover and decreasing enhanced vegetation index.Therefore,algorithms under complex atmospheric and surface conditions(e.g.high AOD,sparse vegetation)should be optimized to improve the accuracy of LSA products.

A detailed comparison of MYD11 and MYD21 land surface temperature products in China's Mainland

Land surface temperature(LST)is a key parameter in land surface system.The National Aeronautics and Space Administration(NASA)recently released new Moderate Resolution Imaging Spectroradiometer(MODIS)LST products(MOD21 and MYD21).Here,we conducted a detailed comparison between the MYD11 and MYD21 LST data in China's Mainland.The LSTs of MYD21 were approximately 1℃ higher than those of MYD11 averaged for China's Mainland,as MYD21 corrected the cold bias of MYD11.The proportions of the valid value of MYD21 were generally lower than those of MYD11 because the cloud removal method of MYD21 was stricter than that of MYD11.Furthermore,the outliers were less significant in MYD11 than in MYD21 because the outliers in MYD11 were removed using temporal constraints on LST.The outliers in MYD21A2 resulted in a difference of greater than 3℃ in average seasonal surface urban heat island intensity(SUHII)between MYD11A2 and MYD21A2.Finally,using MYD11 may underestimate the slope of long-term trends of SUHII.MYD21 LST data may have some uncertainties in urban areas.This study provided a reference for users for selecting LST products and for data producers to further improve MODIS LST products.