286
Remote Sensing and Hydrology' 2000 (Proceedings of a symposium held at Santa Fe, N e w Mexico, U S A ,
April 2000). IAHS Publ. no. 267, 2 0 0 1 .
Remotely sensed estimates of evaporation for
irrigated crops in northern Mexico
JAIME GARATUZA-PAYAN
Insliluto
Mexico
Tecnologico
de Sonora,
5 de Febrero
SI8 Sur, Ciudad
Obregon,
Sonora
85000,
e-mail: [email protected]
W. J A M E S S H U T T L E W O R T H
Department
of Hydrology
Arizona,
Tucson, Arizona
and Water Resources,
85721,
USA
Harshbarger
Building
11, The University
of
R A C H E L T. PINKER
Department
of Meteorology,
Maryland
20742,
USA
Space
Sciences
Building,
University
of Maryland,
College
Park,
C H R I S T O P H E R J. W A T T S
Instituto
Sonora,
del Medio
Mexico
Ambienle
y Desarrollo
de Sonora,
Reyes y Aguascalienles,
Hermosillo,
Abstract Hourly estimates of solar radiation were derived from satellite data
for the Yaqui Valley in Mexico, made on a 50 km grid using the
GEWEX/SRB algorithm applied with GOES-East data and, on a 4 km grid,
using a high-resolution development of the algorithm with GOES-West data.
On average, values derived from GOES-East are 18% greater, while those
from GOES-West are 9% lower than field measurements. After re-calibration,
random differences between hourly satellite estimates and surface observa­
tions remained. These were markedly reduced when daily-average values were
compared. Root mean square error (RMSE) between the satellite and the
surface measurements is lower for the high-resolution satellite estimates than
it is for the low-resolution estimates, and there is a noticeable increase in
apparent structure with the high-resolution data. Finally, the application of the
high-resolution estimates of solar radiation to calculate daily estimates of crop
evaporation for wheat and cotton fields is demonstrated.
K e y w o r d s cotton; évapotranspiration; G O E S ; Makkink equation; Mexico; remote sensing;
solar radiation; Sonora; wheat
INTRODUCTION
Knowledge of evaporation is essential to define irrigation water requirements when
planning, designing, and scheduling irrigation schemes. The Yaqui Valley irrigation
scheme in Mexico is the focus of attention for the research described in this paper,
where timely crop evaporation estimates could provide important information for the
more efficient use of water.
Satellite observations should be of value for estimating evaporation. One success­
ful study, the TiSDat (Timely Satellite Data for Agricultural Management) project
(Diak et al., 1998), used multiple GOES (Geostationary Operational Environmental
Satellite) satellite images available each day to estimate regional evaporation for
Remotely sensed estimates of evaporation for irrigated crops in northern Mexico
287
irrigation scheduling. This encourages further investigation of this approach. Incoming
short-wave solar radiation is the main factor controlling potential evaporation, and
previous studies in the Yaqui Valley have shown that geostationary satellite data can
be used to estimate solar radiation (Stewart et al, 1999). It also has been shown
(Garatuza-Payan et al., 1998) that potential evaporation (XE ), in the Yaqui Valley, can
be estimated from solar radiation and temperature using a locally-calibrated version of
the Makkink equation. The present work explores the potential use of GOES data to
provide daily estimates of crop evaporation in the Yaqui Valley for wheat and cotton
fields through a growing season using the Makkink equation.
P
EXPERIMENTAL AREA, MODELS, MEASUREMENTS AND METHODS
The Yaqui Valley irrigation scheme is located on the coastal plain near Ciudad Obregon
(27°28'N, 109°59'W) in northwest Mexico. The average annual rainfall is 270 mm.
The irrigation scheme covers an area of 40 x 70 km and is made up of a patchwork of
fields of between 25 and 400 ha for different irrigated crops. The main crops are wheat
and cotton with some maize and vegetables, which are grown through-out the year.
The Penman-Monteith equation (Monteith, 1965) is the most widely recognized,
physically-based equation for describing évapotranspiration from uniform vegetation.
However, in the case of irrigated agricultural crops, canopy cover is not always
complete and net radiation is usually strongly determined by solar radiation. For these
reasons, a simpler model has been proposed (the Makkink equation) which has proven
reliable for estimating XE in the Yaqui Valley region (Garatuza-Payan et al, 1998),
and has the form:
P
XE =C -^-R
P
M
S
(1)
A+y
2
where R is the short-wave radiation (W ra ), À is the slope of the saturation vapour
pressure curve (Pa K" ), y is the psychometric constant (Pa K" ), X is the latent heat of
vaporization (J kg" ), and CM is a locally relevant empirical calibration constant. The
value of CM has been determined to be approximately 0.65 on a yearly basis in the
Yaqui Valley (Garatuza-Payan et al, 1992). The term À/(À + y), taking account of the
temperature dependency of the saturation vapour pressure, changes monotonically by
1-2% for a 1°C change in temperature. This implies that the Makkink equation can be
used to derive a daily estimate of XE using only climatological air temperature data
and measurements of the daily total energy incident as solar radiation.
The GEWEX/SRB (Global Energy and Water Cycle Experiment/Surface Radiation
Budget) algorithm (Whitlock et al, 1995), based on the model developed by Pinker &
Lazslo (1992), was used to infer the downward solar radiation at the ground from
satellite observations. In context of the G E W E X Continental Scale International
Project (GCIP), the G E W E X / S R B algorithm is used with data from the GOES-East
satellite to provide satellite estimates of surface and top-of-the-atmosphere radiative
fluxes within one to two days of image capture at one-hourly intervals on an equal area
0.5° grid (Pinker et al, 2001). hi the present study, these data were used to provide the
50 km grid GOES-East satellite-based estimates of solar radiation for the period
November 1998-March 1999.
S
1
1
1
P
288
Jaime Garatuza-Payan et al.
A modified version of the GEWEX/SRJ3 algorithm was implemented and used to
provide estimates on a 4 km grid using data from the GOES-West satellite that were
received at the Instituto Tecnologico de Sonora (ITSON), for the same period. Halfhourly visible images for the area 22.5-36°N and 102-117.5°W were collected, preprocessed, and stored. Image pre-processing involves applying a cloud detection
algorithm, which assumes that any partial cloud cover in a selected target area
increases the spatial variance in the visible radiance over the area. All pixels in a 4 x 4
target area were allocated between clear-sky and totally cloud-covered categories as
explained in Garatuza-Payan et al. (2001).
The daily estimates of potential evaporation were combined with locally-calibrated
crop factors to provide estimates of the actual daily evaporation for individual areas of
crop in the irrigation scheme, following:
F
= K
^ crop, total
where 7\
J
C
v
c ^ M
A
(R , A
s lot
(2)
A +y
1
] is the daily total solar radiation estimated from satellite data in J day" ,
Ticrop.totai is the estimated crop evaporation in m m day" , and K is the appropriate crop
factor for the specific crop and day in the crop growth cycle as provided by GaratuzaPayan er: al. (1998).
To provide validation, the satellite-based estimates of solar radiation were compared
with surface observations in the irrigation region. Solar radiation was measured through­
out the study period with Eppley pyranometers at two sites, Site 910 (27.37°N, 109.92°W)
and Site 1517 (27.20°N; 110.18°W), both sites characterized by irrigated crops.
S]tota
1
c
R E S U L T S A N D DISCUSSION
Table 1 gives the monthly average solar radiation as estimated by the two satellites
using the current satellite calibrations. In both cases, there is an obvious, systematic,
and persistent discrepancy as compared to ground measurements. When the values are
averaged over the whole period for which data are available, the estimates derived
from GOES-East are 18% greater than field data, while those from GOES-West are
9% lower.
For the present study, recognizing the currently poor calibration of GOES-East and
GOES-West, the two satellite estimates were re-calibrated (by - 1 8 % and + 9 % ,
respectively) to give time-average agreement with ground observations. Figure 1
Table 1 Average solar radiation (W m" ) over each month from November 1998 to March 1999 and the
whole study period observed at two sites, Sites 910 and 1517, in the Yaqui Valley irrigation scheme
compared with equivalent estimates made from data from the GOES-East and GOES-West satellites.
Site 910:
Ground
GOES-W
GOES-E
Site 1517:
Ground
November
December
February
March
429
375
467
596
397
312
427
564
524
498
557
668
417
366
483
607
Total
466
426
562
468
GOES-W
GOES-E
405
312
414
552
421
530
495
545
664
559
289
Remotely sensed estimates of evaporation for irrigated crops in northern Mexico
Hourly; Site 9 1 0
(a)
Hourly; S i t e 1 5 1 7
£
g
J
800
700
«600
O
«500
c
o
'« 4 0 0
TD
CO
300
•o
0 1
I
200
LU
100
200
400
600
200
Daily-average: Site 9 1 0
100
400
600
800
Dairy-average: Site 1 5 1 7
200
300
400
500
600
O b s e r v e d Radiation (W m - )
1
700
100
200
300
400
500
600
O b s e r v e d Radiation (W m )
700
!
Fig. 1 Comparison between ground measurements of solar radiation at two sites (910
and 1517) in the Yaqui Valley and the equivalent solar radiation estimated from
satellite: (a) derived at a 4 km grid resolution from GOES-West, and (b) derived at a
50 km grid resolution from GOES-East.
shows a comparison between the resulting hourly average and daily average satellite
estimates vs observed solar radiation at two surface sites. Table 2 shows the root mean
square error (RMSE) of the mean value for hourly and daily averages of solar radia­
tion. The R M S E for daily estimates from GOES-West are in the range 7 - 1 4 %
(30-55 W m" ) and are consistent with results given by other studies (Stewart et al.,
1999). Few authors have reported hourly estimates; however Dedieu et al. (1987)
reported a R M S E of 2 0 % for a study in France, while Stewart et al. (1999) obtained a
R M S E of 20.2% in the Yaqui Valley using a different radiation model. These compare
with the equivalent values found during the present study that lie in the range 9 - 1 4 %
(47-96 W m" ). The daily R S M E values are significantly less than the hourly R M S E
because the satellite provides an instantaneous area-average estimate, while the field
observation is a time-average single-point measurement. Results given in Table 2 and
Fig. 1 show that the high-resolution solar radiation estimates based on GOES-West
data show somewhat better agreement with the surface measurements than do the
lower-resolution estimates based on GOES-East data. The greater resolution in the
spatial distribution given by the 4 km grid should provide more accurate estimates of
incoming solar radiation since more accurate estimates may be obtained for clear and
cloudy areas. This should lead to more reliable estimates of evaporation using field
scale information on crop cover.
2
2
Jaime Garatuza-Payan et al.
290
2
Table 2 Root mean squared errors in W m' , and as a percentage of the average flux (in brackets)
between hourly average and daily average estimates based on GOES-East and GOES-West data, relative
to ground-based observations at sites 910 and 1517.
November
December
February
March
Total
Site 1517:
GOES-West
Site 910:
GOES-West
GOES-East
Hourly
Daily
Hourly
Daily
Hourly
Daily
Hourly
Daily
53.73
(10.35)
66.67
(13.39)
79.69
(13.95)
95.97
(14.23)
42.97
(9.91)
55.36
(14.75)
62.15
(13.48)
53.00
(8.92)
62.24
(12.71)
75.92
(15.79)
91.68
(18.17)
89.57
(14.78)
34.96
(7.78)
41.68
(11.15)
45.95
(9.94)
53.72
(9.11)
46.93
(9.32)
49.03
(10.84)
79.42
(13.4)
77.10
(11.43)
29.93
(7.07)
50.28
(13.75)
63.75
(13.48)
78.08
(12.90)
63.51
(13.17)
71.45
(15.34)
98.48
(18.66)
98.24
(18.54)
46.67
(11.28)
48.96
(13.35)
73.55
(16.17)
54.80
(9.12)
72.83
(13.22)
50.91
(11.17)
80.52
(15.52)
39.21
(9.61)
65.80
(12.06)
53.59
(11.78)
83.65
(16.27)
55.61
(12.35)
GOES-East
Figure 2 demonstrates the feasibility of using satellite data to estimate the evapora­
tion from the component crops in the Yaqui Valley irrigation scheme. This shows the
evaporation estimates during a growth season for two fields, one centred on 27.37°N,
109.92°W which was planted with wheat on 16 November 1998, and one centred on
27.20°N, 110.18°W which was planted with cotton on 1 January 1999. The evapora-
Fig. 2 Evaporation estimates calculated for two fields (a) planted with wheat on
16 November 1998, and (b) planted with cotton on 1 January 1999. In each case, the
daily average net radiation is also shown.
Remotely sensed estimates of evaporation for irrigated crops in northern Mexico
291
tion estimates are derived by multiplying the daily estimates of potential evaporation
for each field by the relevant crop factor as specified by Garatuza-Payan et al. (1998).
The estimate of potential evaporation used in these calculations is that given by the
Makkink equation from the high-resolution (4 km) satellite estimates of solar radiation
for each field.
Acknowledgements Primary support for this analysis at The University of Arizona
was provided under N A S A Grant NAG8-1531. In addition, Jaime Garatuza-Payan
received support under a C O N A C Y T Fellowship and project 29340T. The satellite
data from GOES-West were gathered as part of research supported by the European
Union (CI1-CT94-0059).
REFERENCES
Dedieu, G., D e s c h a m p s , Y. & Kerr, Y. H. ( 1 9 8 7 ) Satellite estimation of solar irradiance at the surface of the Earth and
surface a l b e d o using a physical model applied to Meteosat data. J. Appl. Met. 26, 7 9 - 8 7 .
Diak, G. R., A n d e r s o n , M . C , Bland, W . L., N o r m a n , J. M . , Mecikalski, J. M . & A u n e , R. M . ( 1 9 9 8 ) Agricultural
m a n a g e m e n t decision aids driven b y real-time satellite data. Bull. Am. Met. Soc. 7 9 ( 7 ) , 1 3 4 5 - 1 3 5 5 .
G a r a t u z a - P a y a n , J., Pinker, R. T. & Shuttleworth, W. J. ( 2 0 0 1 ) High resolution cloud observations for N o r t h w e s t M e x i c o
from G O E S - 7 satellite data. J. Atmos.
Ocean
Technol.\0S(\),
39-56.
G a r a t u z a - P a y a n , J., Shuttleworth, W . J., M c N e i l , D . D., Stewart, J. B . , D e Bruin, H. & W a t t s , C. ( 1 9 9 8 ) M e a s u r e m e n t and
m o d e l l i n g evaporation for irrigated c r o p s in N o r t h w e s t M e x i c o . Hydrol.
Processes
12, 1 3 9 7 - 1 4 1 8 .
G a r a t u z a - P a y a n , J., W a t t s , C. J. & Cervera, L. E. ( 1 9 9 2 ) Estimacion d e evapotranspiracion p o t e n t i a l en el Valle del Yaqui
(Potential évapotranspiration estimates in the Yaqui Valley). In: XII Congreso
de Hidraulica
(Puerto Vallarta,
Mexico).
Monteifh, J. L. ( 1 9 6 5 ) E v a p o r a t i o n and environment. In: Proc. Symp. of the Society
of Experimental
Biology
19, 2 0 5 - 2 3 4 .
Pinker, R. T., Tarpley, J. D . , Laszlo, I. & Mitchell, K. ( 2 0 0 1 ) Surface radiation b u d g e t s in s u p p o r t of the G E W E X
Continental Scale International Project ( G C I P ) . J. Geophys.
Res. (submitted).
Pinker, R. T. & L a z l o , I. ( 1 9 9 2 ) M o d e l i n g surface solar irradiance for satellite applications o n a global scale. J. Appl. Met.
31(2), 194-211.
Stewart, J. B . , W a t t s , C. J., Rodriguez, J. C , D e Bruin, H. A. R., V a n den B e r g , A. R., G a r a t u z a - P a y a n , J. ( 1 9 9 9 ) U s e of
satellite data to estimate radiation and evaporation for northwest M e x i c o . Agric. Wat. Manage. 3 8 , 1 8 1 - 1 9 3 .
W h i t l o c k , C. H., Charlock, T. P., Staylor, W . F., Pinker, R. T., Laszlo, L, O h m u r a , A., Gilgen, H., K o n z e l m a n , T.,
D i P a s q u a l e , R. C , M o a t s , C. D., LeCroy, S. R. & Ritchey, N . A. ( 1 9 9 5 ) First global W C R P s h o r t w a v e surface
radiation b u d g e t data set. Bull. Am. Met. Soc. 7 6 ( 6 ) , 1-18.