Energy balance and evaporation loss of an agricultural reservoir in a semi-arid climate (south-eastern Spain)

✍ Scribed by B. Gallego-Elvira; A. Baille; B. Martín-Górriz; V. Martínez-Álvarez

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 473 KB
• Volume: 24
• Category: Article
• ISSN: 0885-6087
• DOI: 10.1002/hyp.7520

✦ Synopsis

Abstract

A typical agricultural water reservoir (AWR) of 2400 m^2^ area and 5 m depth, located in a semi‐arid area (southern Spain), was surveyed on a daily basis for 1 year. The annual evaporation flux was 102·7 W m^−2^, equivalent to an evaporated water depth of 1310 mm year^−1^. The heat storage rate G exhibited a clear annual cycle with a peak gain in April (G ∼ 45 W m^−2^) and a peak loss in November (G ∼ 40 W m^−2^), leading to a marked annual hysteretic trend when evaporation (λ__E__) was related to net radiation (R~n~). λ__E__ was strongly correlated with the available energy A, representing 91% of the annual AWR energy loss. The sensible heat flux H accounted for the remaining 9%, leading to an annual Bowen ratio in the order of 0·10. The equilibrium and advective evaporation terms of the Penman formula represented 76 and 24%, respectively, of the total evaporation, corresponding to a annual value of the Priestley–Taylor (P–T) coefficient (α) of 1·32. The P–T coefficient presented a clear seasonal pattern, with a minimum of 1·23 (July) and a maximum of 1·65 (December), indicating that, during periods of limited available energy, AWR evaporation increased above the potential evaporation as a result of the advection process. Overall, the results stressed that accurate prediction of monthly evaporation by means of the P–T formula requires accounting for both the annual cycle of storage and the advective component. Some alternative approaches to estimating R~n~, G and α are proposed and discussed. Copyright © 2009 John Wiley & Sons, Ltd.