463
Remote Sensing and Modeling of Global Evapotranspiration
the literature (Calder et al. 1986; Bruijnzeel 1990; Frank and Inouye 1994; Leopoldo
et al. 1995; Liski et al. 2003; Kumagai et al. 2005; Pejam et al. 2006).
Precipitation is not an input to the ET algorithm, and over a relatively long period,
ET should be less than precipitation according to the water balance theory. Figure
19.9a shows that the MODIS ET is less than precipitation according to Chen et al.
0
150
300
450
Global annual MODIS ET (2000−2006) mm ∙ year –1
600
750
900
FIGURE  19.8  Mean global ET driven by interpolated GMAO meteorological data and
0.05° resolution MODIS data during 2000–2006 with a maximum ET of 1092 mm ∙ year –1
and an area-weighted average ET of 351 ± 221 mm ∙ year –1 for vegetated land areas.
(a)
(b)
4000
3500
3000
2500
2000
1500
1000
500
0
4000
3500
3000
2500
2000
1500
1000
500
0
0
500
1000
Mean annual ET (mm ∙ year –1 )
Mean annual ET (mm ∙ year –1 )
Mean annual GPP (g C/m 2
/year)
Mean annual precipitation (mm∙year ‒1
)
1500
0
500
1000
1500
FIGURE 19.9  (a) Mean annual total precipitation and (b) mean annual total MODIS GPP
versus annual total ET (driven by GMAO meteorological data) during 2000–2006. The solid
line in (a) represents a 1:1 ratio.