Flood projections for selected Costa Rican main basins using CMIP6 climate models downscaled output in the HBV hydrological model for scenario SSP5-8.5

Abstract

Estimates from 3 statistically downscaled General Circulation Models (GCMs) from version 6 of the Coupled Model Intercomparison Project, namely the EC Earth3, GFDL ESM4 and MPI ESM1 2 HR are used in the HBV hydrological model to estimate design streamflow projections with 20, 50, and 100-year return periods for the selected main basins of Costa Rica. The changes in these streamflows were computed between the baseline period (1985–2015) and the mid-century projection (2035–2065) for the SSP5-8.5 scenario. The novelty resides in being the first study that explores the magnitude of climate changes in design flows of Costa Rica, a tropical country. Although, calibration and validation statistics are generally good for most of the basins, only around one quarter of the simulations reproduce the observed distribution of the 3-day annual maximum flows. Results show that the MPI model presents lower sensitivity with changes of different sign depending on the basin studied and the other two models suggest only significant increases in the design flow in most of the basins. Results of the model’s ensemble suggests a great concern, as there is a general increase in the design flows, and the magnitudes of the changes are large, especially in the Pacific slope.