Modeling Evapotranspiration in a Sub-Tropical Climate

Salalah is situated on a fresh water aquifer that is replenished during the annual monsoon season with an average vertical precipitation (rainfall) of 245 mm/yr in Jabal AlQara and 104 mm/yr in the Salalah plain. The aquifer is the only source of water for Salalah city. A rainfall and mist precipitation in the Jabal AlQara recharges theplain with significant renewable fresh groundwater resources that have allowed agricultural and industrial development to occur. In Salalah city where groundwater has been used extensively since the early 1980s for agricultural, industrial and municipal purposes, the groundwater resource has been withdrawn from the aquifer more rapidly than it can be replenished by natural recharge. In turn, the heavy withdrawal of large quantities of the groundwater from the aquifer has lead to intrusion of sea water. Agricultural activities usually utilize over 70% of the groundwater. In order to investigate the salinity intrusion and nitrate pollution, the study area was divided into four strips on the basis of land use plans in the area. Water samples were collected from 18 water wells. Chemical analysis of basic ions and pollution parameters in natural waters was carried out. The electrical conductivity, chloride and nitrate concentrations were highest in the agricultural and residential strips, and Garziz grass farm. The present status of groundwater quality in most of the agricultural and residential strips does not meet drinking water standards. The study suggests an approach to protect the groundwater in the Salalah plain aquifer from further encroachment, by artificial recharge with reclaimed water, preferably along the Salalah coastal agricultural strip. This scheme can also be applied to other regions with similar conditions.