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Figure 4 and Table 3 show the relationships between ETMODIS and the four GLDAS evapotranspiration datasets (monthly time steps) from 2003 to 2012. r, and were 0.99 (P < 0.05), 10.3 and −4.3 mm/month (i.e., MODIS data under-estimate GLDAS evapotranspiration), respectively, where ETMODIS is compared to the average of the four GLDAS datasets. At annual time steps, was 51.9 mm/yr for the YRB, which accounted for 5% of POBS (shown in Table 2). for the upper reaches of the YRB was smaller than that for the middle reaches of the YRB at the two time steps. In addition, r was 0.95 (P < 0.05) between the monthly ETMODIS and ETOBS from Qianyanzhou station although the observed time series was short (Figure 4(c)). shows that ETMODIS was 13.5 mm/month larger than ETOBS on average. was 14.3 mm/month, accounting for 16% of the YRB POBS.
Table 3

Relationship between MODIS product and GLDAS evapotranspiration

BasinRelationshipCLMMOSAICVICNoahAverage
YRB r 0.98** 0.98** 0.99** 0.98** 0.99** 
(mm/month) 8.5 16.7 16.1 7.5 10.3 
(mm/month) 7.8 −14.0 −8.7 −2.4 −4.3 
Upper reaches of the YRB r 0.99** 0.98** 0.98** 0.98** 0.99** 
(mm/month) 10.3 16.2 16.3 9.9 12.5 
(mm/month) 6.2 −10.1 −4.7 0.2 −2.1 
Middle reaches of the YRB r 0.97** 0.97** 0.98** 0.97** 0.98** 
(mm/month) 11.2 19.8 17.5 9.0 9.5 
(mm/month) 10.4 −18.7 −13.5 −6.3 −7.0 
BasinRelationshipCLMMOSAICVICNoahAverage
YRB r 0.98** 0.98** 0.99** 0.98** 0.99** 
(mm/month) 8.5 16.7 16.1 7.5 10.3 
(mm/month) 7.8 −14.0 −8.7 −2.4 −4.3 
Upper reaches of the YRB r 0.99** 0.98** 0.98** 0.98** 0.99** 
(mm/month) 10.3 16.2 16.3 9.9 12.5 
(mm/month) 6.2 −10.1 −4.7 0.2 −2.1 
Middle reaches of the YRB r 0.97** 0.97** 0.98** 0.97** 0.98** 
(mm/month) 11.2 19.8 17.5 9.0 9.5 
(mm/month) 10.4 −18.7 −13.5 −6.3 −7.0 

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

Figure 4

(a) Time series of evapotranspiration datasets from MODIS and GLDAS for the YRB during 2003–2012 (the grey area represents the range of the four GLDAS evapotranspiration datasets and the black dashed line represents the GLDAS average); (b) relationship between ETMODIS and the four datasets of GLDAS evapotranspiration; and (c) distribution of ETMODIS and ground-based measurements of ETFLUX during 2003–2004. ** indicates that the relationship is significant at the level of 0.05 by T-test.

Figure 4

(a) Time series of evapotranspiration datasets from MODIS and GLDAS for the YRB during 2003–2012 (the grey area represents the range of the four GLDAS evapotranspiration datasets and the black dashed line represents the GLDAS average); (b) relationship between ETMODIS and the four datasets of GLDAS evapotranspiration; and (c) distribution of ETMODIS and ground-based measurements of ETFLUX during 2003–2004. ** indicates that the relationship is significant at the level of 0.05 by T-test.

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