Assessment of Water Balance of the Semi-Arid Region in Southern San Joaquin Valley California Using Thornthwaite and Mather's Model

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Growing population and irrigation needs increase the demand for water requiring judicious use of limited fresh water resources. The Paramount farm in Southern San Joaquin valley, California, the world's largest supplier of almonds, is facing a problem of water storage. The resource is estimated by a water balance assessment approach using the Thornthwaite and Mather (TM) models. The result shows that high soil moisture storage occurs from November to February in the range of 25 to 36 mm, but least in May to August as evapotranspiration is a maximum in May-July. This study also illustrates that there is highest recharge of soil moisture in November to January. To avoid crop water stress, irrigation should occur when the absolute value of accumulated potential water loss is maximum in the months of May to July. The water balance calculation shows that the maximum annual runoff is from January to March and October to December. There is an annual water deficit of 135 mm and an annual surplus of about 2 mm at the farm. This area has a period of moisture surplus from November to February and the remaining months are the period of deficit.

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