Modeling fast and slow flows with the SAC-SMA model to improve hydrological forecasting in watersheds in the Andean Region of Colombia

Abstract:

An increased understanding of the uncertainties in hydrology models can lead to improved confidence in streamflow forecasts. Hydrological modeling results are subject to uncertainty due to model structure, model parameters, and input data. All model structures are not necessarily suitable for all hydroclimatic regions. The Andean region of Colombia generates scientific interest in hydrology due to the complex topography, climate variability, and soil texture. In addition, around 70% of the Colombian population is settled in this region. The present study evaluates the simulated total discharge, the fast and slow flows obtained with the SAC-SMA model for 8 Colombian watersheds located in the Andean region with different climate regimes (unimodal, bimodal, mixed, and aseasonal regimen) and with different soil index (based on the soil texture). Watershed size ranges from 600-2000 km² and the model simulation period from 11 to 20 years. The model calibration was performed using a Multistep Automatic Calibration Scheme coupled with the Shuffled Complex Evolution (SCE-UA) optimization algorithm. SAC-SMA Model performance was evaluated with Distance Root Mean Square (DRMS), LOG, Bias and Nash-Sutcliffe (NSE). The rainfall spatial averaged is estimated using the inverse distance weighting (IDW) method with the available rain gauges, while potential evapotranspiration data is obtained from MODIS satellite images. Soil texture is obtained from the Agustín Codazzi Geographic Institute (IGAC) and Land cover data from Sentinel 2 satellite. The NSE ranges between 0.6-0.8 for the studied watersheds. The simulation of fast and slow flows shows differences between the climate regimens and soil index. Understanding the dynamics of both flows and their connections with climate regimes and soil texture and cover is important for water resources management in the Andean region. This study also provides information for flood prevention, land-use planning, and development of public policies in the country.