www.nature.com/scientificreports OPEN A comparison of diferent GRACE solutions in terrestrial water storage trend estimation over Received: 4 June 2018 Accepted: 19 December 2018 Tibetan Plateau Published: xx xx xxxx Wenlong Jing1,2,3, Pengyan Zhang4,5,6 & Xiaodan Zhao1,2,3 The Gravity Recovery and Climate Experiment (GRACE) terrestrial water storage anomalies (TWSA) estimations provide valuable information for the monitoring of land water resources changes. Multiple parameters and strategies for inversion of the water storage changes have been explored. The explorations on diferences between GRACE solutions in local regions and basins are fundamental and important. This study focuses on comparisons of TWSA trends between diferent GRACE solutions over Tibetan Plateau (TP), both storage and fux among solutions were compared. Results show that great discrepancies exist in TWSA between GRACE solutions derived from the standard spherical harmonic approach (SSH) and the mascon approach. Three SSH-based GRACE solutions (JPL, CSR, and GFZ) detect no signifcant TWSA changes for the whole area of Tibetan Plateau, whereas JPL mascon solution (JPL-M) and CSR mascon solution (CSR-M) gave decreasing trends of 3.10 km3/yr and 3.77 km3/yr, respectively. This diference also exists in the Yangtze River-Yellow River basin (YYR basin) in the TP. Although fve solutions derived consistent TWSA trends in northwest river basin (NWR basin) and southwest river basin (SWR basin) in the TP, the variations between diferent solutions are 2.88 km3/yr and 4.75 km3/yr for NWR and SWR basin respectively, which could not be neglected. The JPL-M solution, as a result, would overestimate both TWSA decreasing and increasing trends comparing with other GRACE solutions. The results of this study are expected to provide references for the studies of water resource dynamics over Tibetan Plateau and the surrounding areas based on GRACE TWSA products. Monitoring water resources dynamics over Tibetan Plateau is extremely important for understanding the global water cycle and the regional responses to climate change over Tibetan Plateau and the surrounding areas1–3. It is helpful for water resources management and drought events detections over China and South Asian countries4,5. Te Gravity Recovery and Climate Experiment (GRACE) twin satellites, which were launched in 2002, have provided global monthly land or terrestrial water storage anomalies (TWSA) by measuring Earth’s gravity feld changes6. Te TWSA includes water storage anomalies of fve components: snow water, canopy water, surface water, soil water, and groundwater7. Te GRACE TWSA can reveal total water availability variations both storage and fux at continental scales8,9. Latest released versions of GRACE TWSA products include Spherical Harmonic Data Versions and Mascon Data Versions. Te Spherical Harmonic Data Versions are processed by using a stand- ard spherical harmonic approach6, and the Mascon Data Versions are produced by using mass concentration blocks (mascons)10. Tree diferent processing centers, which are the GeoforschungsZentrum Potsdam (GFZ), the Center for Space Research at University of Texas, Austin (CSR), and the Jet Propulsion Laboratory (JPL), release diferent solutions by using diferent approaches and parameters. 1Guangzhou Institute of Geography, Guangzhou, 510070, China. 2Key Laboratory of Guangdong for Utilization of Remote Sensing and Geographical Information System, Guangzhou, 510070, China. 3Guangdong Open Laboratory of Geospatial Information Technology and Application, Guangzhou, 510070, China. 4College of Environment and Planning, Henan University, Kaifeng, 475004, China. 5Institute of Agriculture and rural Sustainable Development, Henan University, Kaifeng, 475004, China. 6Collaborative Innovation Center on Yellow River Civilization of Henan Province, Henan University, Kaifeng, 475001, China. Correspondence and requests for materials should be addressed to P.Z. (email: [email protected]) SCIENTIFIC REPORTS | (2019) 9:1765 | https://doi.org/10.1038/s41598-018-38337-1 1 www.nature.com/scientificreports/ Figure 1. Spatial pattern of terrain and basin boundary of Tibetan Plateau (created by using QGIS 3.2: https:// www.qgis.org/en/site/). Tese GRACE TWSA solutions, produced using diferent approaches by diferent centers, have been widely used for evaluation of water resources changes over large-scale regions and basins11–16. For TP, several researches have been conducted for the estimation of water mass balance based on the GRACE TWSA solutions. According to Jacob, T. et al.17, the TWSA over TP experienced an increasing at trend of 7.0 km3/yr from 2003 to 2010, which was obtained based on GRACE CSR mascon (CSR-M) solution. Te TWSA trend over TP estimated from Guo, J. et al.18 based on GRACE CSR solution was 5.3 km3/yr during 2003 to 2012. However, the results from Pengkun, X. U. et al.19 indicated the TWSA decreased from 2005 to 2010 at a trend of −3.64 km3/yr, which the conclusion was drawn from estimations based on released version 4 of CSR solution (CSR-RL04). As can be seen that the TWSA trends estimated from diferent GRACE solutions revealed diferent water resource variations over TP. Such discrepancies between diferent GRACE solutions can also be found over some other basins around the world7. Diferences between diferent GRACE solutions can lead to great discrepancies in TWSA trend estima- tions. Terefore, quantifying those discrepancies is signifcant and urgent for understanding uncertainties in monitoring water resources variations based on GRACE outputs at both continental and basin scales. Te objective of this study is to explore diferences between GRACE solutions over Tibetan Plateau and evalu- ate the uncertainty arises from the choice of diferent GRACE solutions. Both storage and fuxes among GRACE solutions were compared. In addition, spatial pattern of GRACE TWSA trends and the variations among diferent GRACE solutions were also analyzed. Te results of this study are expected to provide direct reference for the researches involving water resources dynamics over TP and the surrounding areas by using GRACE-derived products. Study area and data resources. Study area. Te Tibetan Plateau (TP) is the highest plateau on the earth, which is located between 26°00′N and 39°47′N, and 73°19′E and 104°47′E. Te TP stretches from the southern margin of the Himalayas to the north, to the Kunlun Mountains, the Altun Mountains, and the northern margin of the Qilian Mountains. In the west, the Pamirs and Karakoram Ranges, and the east and northeast connect with the western section of the Qinling Mountains and the Loess Plateau20,21 (Fig. 1). Te map in Fig. 1 was created by using the mapping tool in an open source sofware QGIS 3.2 (https://www.qgis.org/en/site/). Te average altitude of TP is over 4000 meters above sea level22, thus it is commonly referred to as the “Roof of the World”20. Te TP is the headstream of many rivers in East Asia, Southeast Asia and South Asia23. A number of world-class rivers fowing down from the Tibetan Plateau to the southeast, fowing into the sea, such as the Yarlung Zangbo River, Lancang River, and Nu River. Te Yangtze River and the Yellow River, which are known as the mother rivers of Chinese people, also originate from east Tibetan Plateau24. Continental rivers are mainly located in the northwest part of TP. Te Yarlung Zangbo River, Lancang River, Nu River, which fow to the Indian Ocean, are in the southwest TP. Te Yangtze River and Yellow River originate from east TP and fow down to the Pacifc Ocean. Terefore, the TP is divided into three basins: the northwest river basin (NWR basin), the southwest river basin (SWR basin), and the Yangtze River and Yellow River basin (YYR basin). Te area of each basin is 1336460 km2 (NWR basin), 628921 km2 (SWR basin), and 658504 km2 (YYR basin) (Fig. 1). GRACE data. Te RL05 spherical harmonics. Te Gravity Recovery and Climate Experiment (GRACE) twin satellites were launched in 2002. GRACE satellites provide global monthly total water storage anomalies by meas- uring Earth’s gravity feld changes. Te spherical harmonic approach (SSH) is the standard for the frst decade of GRACE observations6,25. Te ofcial GRACE Science Data System continuously released monthly GRACE solu- tion for three diferent processing centers: GeoforschungsZentrum Potsdam (GFZ), Center for Space Research SCIENTIFIC REPORTS | (2019) 9:1765 | https://doi.org/10.1038/s41598-018-38337-1 2 www.nature.com/scientificreports/ at University of Texas, Austin (CSR), and Jet Propulsion Laboratory (JPL). Tese three solutions used diferent parameters and strategies, such as diferent degree and order, spherical harmonic coefcient, spatial flter and smoothing factor26. Te current solutions are the Release-05 gravity feld solutions (RL05). Te three GRACE terrestrial water storage (TWS) solutions (JPL, CSR, and GFZ) were downloaded from https://grace.jpl.nasa. gov/data/get-data/monthly-mass-grids-land/. Te original data were provided at 1 degree in both latitude and longitude and resampled at 0.5 degrees. Te Global Mascons. Mass Concentration blocks (mascons) are another form of gravity feld basis function. Te “mascon” make the implementing of geophysical constraints much easier and is a much more rigorous approach comparing with the standard spherical harmonic approach of empirical post-processing fltering27,28. Te JPL mascon (JPL-M) and CSR mascon (CSR-M) solutions were provided at 0.5 degrees at https://grace.jpl.nasa.gov/ data/get-data/monthly-mass-grids-land/.