Groundwater from Clouds – Coupling a Regional Groundwater Model with Recharge Scenarios Based on Cloud Forest Distribution in Oman

Abstract:

The Dhofar mountain range in southern Oman divides the semi-arid coastal plain to the South from the arid desert region to the North of the mountain range. The demand for fresh water in the region is almost exclusively covered by groundwater. Possible sources for groundwater recharge in Dhofar are the monsoon season – which is unique for the Arabian Peninsula - and rare storm events reoccuring infrequently every 3 to 7 years. The present study focuses on the recharge potential of the monsoon and the role of the Dhofar cloud forest. The monsoon with its orographic rainfall distribution is the most reliable source of precipitation for the Dhofar area, but is limited to the south side of the mountains. Every year between June and September light rain and fog is brought to the area, yielding mean rainfall values of 104 mm per year in the plain and 299 mm per year at high elevations. This results in higher spring discharge at the foot of the mountains and subsurface recharge into the coastal plain. Results from previous ecohydrological studies on the Dhofar cloud forest hydrology suggest that the recharge potential in forested regions is substantially higher than from other land cover in the region. Reasons for this lie in the ability of forested regions to capture cloud water or fog and the interception processes, specifically stemflow, that channel substantial amounts of water directly into deeper soil layers. In short, the cloud forest land cover receives fog water in addition to rainfall and the interception processes result in preferential pathways below the forest. The different recharge potential of cloud forest areas versus a classic distributed infiltration pattern caused by regular rainfall as well as the spatial distribution of the cloud forest has been used to formulate different recharge scenarios. A groundwater flow model was developed reproducing the north-to south gradient and the observed heads and outflows at the foot of the mountain. Different recharge scenarios were used to run the flow model with the aim to assess the effect of major land cover changes in the recharge zone of the Salalah coastal plain. Currently the cloud forests are under pressure from deforestation by livestock. To what extent de- or even re-forestation will affect groundwater resources in the Salalah coastal plain will be assessed through the study.