Simulation of Climate Change Impacts in the Water Balance of a Tropical Groundwater Basin in South-Central Panama

In the Pacific region of Central America, groundwater recharge is favored by high intensity rainfall events occurring mostly in September and October due to seasonal migration of the inter-tropical convergence zone (ITCZ). Across the tropics, high intensity rainfall events are expected to increase in frequency due to climate change, thus favoring groundwater recharge in these areas. For Panama, climate change scenarios suggest that precipitation will increase towards the second half of the 21st century and that extreme events will be more likely. In the Dry Arc Region, located in south-central Panama, streamflow greatly diminishes during the dry season (January April) and thus groundwater is heavily used for irrigation and human consumption in rural areas. In general, this area of Panama receives 90% of its rainfall during the wet months and only 10% during the dry months. However, in the past decade there have been years where the dry season lasted for 5 to 7 months. As precipitation patterns continue to shift due to climate change, it is crucial to understand and quantify its effects on groundwater recharge, groundwater levels and the interaction between groundwater and surface water (GW-SW) for this area of Panama. A hydrogeological numerical model of the Estibaná River sub-catchment (ERSC), located in the Dry Arc Region, was built using MODFLOW. Climate change effects on the water balance for ERSC were evaluated using downscaled projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6). For the baseline scenario, groundwater recharge in the ERSC corresponds to nearly 2.5% of the total yearly precipitation. Regarding GW-SW interactions, it was estimated that contributions from the aquifer to the river range from 200 to 800 m3/day. Also, contributions from the river to the aquifer are in the order of 100 m3/day. By employing downscaled climatic projections, information regarding volume and timing of groundwater recharge as well as GW-SW interactions, future water availability in the ERSC is forcasted. Therefore, this approach might be a valuable tool for other seasonally dry tropical basins.