Joint modeling of canopy interception and soil water flow to compare infiltration rates below two land covers (Galápagos Islands)

Tuesday, 16 December 2014
Christian Dominguez1,2, Alexandre Pryet3, Andres Gonzalez4, Julien Tournebize5, Cédric Chaumont5, Marcos Villacis4, Noemi I D'ozouville6 and Sophie Violette1,2, (1)University Pierre and Marie Curie Paris VI, Paris, France, (2)Ecole Normale Supérieure Paris, UMR.8538 - Laboratoire de Géologie, Paris, France, (3)University Michel de Montaigne Bordeaux 3, EA 4592 Géoressources & Environnement, Pessac Cedex, France, (4)National Polythecnic School, Department of Civil and Environmental Engineering, Quito, Ecuador, (5)IRSTEA, Antony Cedex, France, (6)Charles Darwin Foundation, Santa Cruz, Ecuador
Most volcanic islands face issues due to an imbalance between constantly increasing population and limited freshwater resources. In this context, groundwater exploitation is a valuable strategy and the estimation of recharge rates is crucial for water management planning, specially considering the changes in land use.

In the present study we aim to assess the impact of land cover change on the groundwater recharge at the Santa Cruz Island (Galápagos), where a marked vegetation zonation is observed on the windward side. We studied during one year two adjacent land covers that extend on the majority of the island: a secondary forest and a pasture land.

We monitored the climatic variables and throughfall over the pasture and under the forest, respectively. At both plots, the soil water suction was measured with automatic tensiometers in a vertical profile at different soil depth. We associate (i) a Rutter-type canopy interception model, with (ii) a 1-D physically-based variably saturated flow model. This allows the estimation of interception losses, cloud water interception, plant transpiration, runoff and deep percolation. The model was calibrated with the throughfall and soil water suction measurements.

The model reveals contrasting behaviors in the soil water transfers between the two plots. The difference could be attributed to the reduction of the net precipitation input at the forest, which is caused by higher evaporation losses at the canopy. The approach provides insights about the soil water dynamics under different land covers, and may help to assess the effect of land use change in the groundwater recharge of a vast region of the island.