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Table 4 shows the relationships between trends in satellite products and ground-based/model-based datasets for the YRB at monthly time steps. The only clear relationships were obtained for precipitation. This suggests that monthly time series of MODIS, GRACE and estimated stream flow were not suitable for identifying temporal trends in these components of the YRB water balance, despite there being good correlations in the absolute values. Table 5 shows the comparison of water balance component trends using annual time series. For the entire YRB, the rates of changes in PTRMM, ETMODIS, and QRS are 173%, 318%, 240% and 83%, respectively, of corresponding ground-based/model-based slope. Although the rates of changes in satellite-based water balance components for the upper reaches of the YRB are extremely large due to the slight trends in QOBS and ETGLDAS, the rates of changes in satellite-based water balance components for the middle reaches of the YRB are within 129–170%. Generally, the satellite products are more suitable for studying the trends in annual time series compared with monthly time series.

Table 4

Correlation coefficient between trends in satellite products and ground-based/model-based datasets at monthly time steps

BasinPTRMM vs. POBSETMODIS vs. ETGLDASaΔSGRACE vs. ΔSWBQRS vs. QOBS
YRB 0.84** 0.60** 0.35 −0.07 
Upper reaches of the YRB 0.80** −0.15 −0.34 −0.11 
Middle reaches of the YRB 0.90** 0.43 0.51** 0.31 
BasinPTRMM vs. POBSETMODIS vs. ETGLDASaΔSGRACE vs. ΔSWBQRS vs. QOBS
YRB 0.84** 0.60** 0.35 −0.07 
Upper reaches of the YRB 0.80** −0.15 −0.34 −0.11 
Middle reaches of the YRB 0.90** 0.43 0.51** 0.31 

aCalculated by the average values of the four GLDAS datasets.

**Indicates that relationship is significant at the level of 0.05 by T-test.

Table 5

Trends in water balance components based on satellite products in the YRB from 2003 to 2012 (mm/yr2)

BasinPTRMMPOBSETMODISETGLDASaΔSGRACEΔSWBQRSQOBS
YRB 6.9 4.0 −3.5** −1.1 7.2* 3.0 1.9 2.3 
Upper reaches of the YRB −1.4 −3.7 −3.1 0.4 5.3* 2.3 −2.9 0.1 
Middle reaches of the YRB 16.4 12.7 −4.2** −3.0 9.7 5.7 8.8 5.5 
BasinPTRMMPOBSETMODISETGLDASaΔSGRACEΔSWBQRSQOBS
YRB 6.9 4.0 −3.5** −1.1 7.2* 3.0 1.9 2.3 
Upper reaches of the YRB −1.4 −3.7 −3.1 0.4 5.3* 2.3 −2.9 0.1 
Middle reaches of the YRB 16.4 12.7 −4.2** −3.0 9.7 5.7 8.8 5.5 

aCalculated by the average values of the four GLDAS datasets.

*Indicates that slope is significant at the level of 0.01 by T-test.

**Indicates that slope is significant at the level of 0.05 by T-test.

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