Cai, J; Liu, Yu; Lei, T; Pereira, LS
Real-time irrigation management and water resources
allocation need real-time prediction of daily reference evapotranspiration (ETo). Thus, adopting
the FAO Penman-Monteith (FAO-PM) equation as the standard for ET, estimation, an attempt was made
to predict daily ETo using the public weather forecast messages available in China. These involve
the cloudiness conditions, daily maximum and minimum temperature, and wind speed scales. An
analytical method (AM) was developed to translate daily weather forecast messages into the
variables needed to estimate ETo. Daily weather data for the period 1984-1998 at eight
meteorological stations representing a wide range of climatic conditions of China were used to
compute the FAO-PM ET, and to serve as reference data sets for comparison with the variables
obtained from daily weather forecast messages at the same locations and period. Several
statistical indicators were used for the respective comparisons. The sunshine duration (n)
estimated from the forecasted cloudiness agree well with those observed as indicated by the
Willmott indices of agreement, d, and the determination coefficient, R-2, higher than 0.99 and
0.96, respectively, at all locations. The translation of wind speed scales into wind speed values
shows adequate, with a relative error, RE, near 0.10 and high values for d and R-2. The
comparison of the actual vapour pressure estimated from the minimum temperature and computed from
air humidity observations yielded d and R-2 values higher than 0.85 for all the locations except
one, Ejina, located in an and region. The estimated weather parameters were then used to compute
the daily ETo, with the FAO-PM equation for the eight locations. The weather forecasted ETo
estimates agree well with the ETo values computed with full data sets, with d and R-2 for all
locations larger than 0.95 and 0.91, respectively. However, the accuracy of these ET, estimations
depends upon the availability of accurate weather forecast messages. Results indicate that daily
ET. predictions using the public weather forecast messages are appropriate to be used for real-
time water allocation and irrigation management. (c) 2007 Elsevier B.V. All rights reserved.