Assessing CFSR climate data for rainfall-runoff modeling over an ungauged basin between Iraq and Iran

Abstract

In most developing countries, networks of gauge observations are frequently sparse and may have significant spatial and temporal gaps in the meteorological records. Reanalysis products are extensively used as alternative climate inputs for watershed modeling that provide continuous data worldwide. However, the direct utilization of such products is highly doubtful at different basin scales. This article aims to evaluate the accuracy of the Climate Forecast System Reanalysis (CFSR) product for streamflow simulation using the Soil and Water Assessment Tool (SWAT) model in the northeastern part of the Little Zab River Basin (LZRB), a mountainous basin between Iraq and Iran. The quality of CFSR was assessed from two viewpoints: (1) the precipitation aspect, an analysis of the CFSR precipitation compared to observational meteorological data (OMD) from 2004 to 2013 on a daily time scale, and (2) the hydrology aspect, a comparison of the SWAT model performance based on OMD (scenario I) and the CFSR product (scenario II) for monthly streamflow simulations. Results showed that the CFSR precipitation had a satisfactory correlation with rain gauge data ranging from 0.55 to 0.81. The performance of OMD in SWAT-based streamflow simulation achieved a ‘very good’ rating in calibration (2006–2010) and validation (2011–2013). Meanwhile, the CFSR-based model demonstrated a ‘very good’ hydrologic prediction skill in calibration. In contrast, CFSR revealed a lower performance in the validation period as it considerably overestimated base and peak flows in LZRB. Nevertheless, model uncertainty analysis after calibration showed that more than 88% of measured streamflow values at the basin outlet were bracketed within the 95 percent prediction uncertainty (95PPU) band for OMD and CFSR. These findings revealed that the CFSR product, after proper bias correction, could be a reliable alternative climate input for hydrologic modeling and climatological studies in semi-arid basins where gauge data is limited.