Coupling simulation of water-carbon processes for catchment―calibration and validation of the WaSSI-C model

Abstract

Aims The water-carbon coupling model has become a major approach of eco-hydrology study under the complicated situation of climate changes. Our objective was to explore the applicability of the WaSSI-C model for the humid region in southwestern China. Methods We focused on a large watershed, the upper Zagunao River watershed, situated in the upper reach of the Minjiang River, Yangtze River Basin. Applicability of the WaSSI-C model was assessed by evaluating the modeling results with two indexes: determination coefficient (R2) and Nash-Sutcliffe efficiency coefficient (NS). In order to make it better suited for the study area, two main improvements were introduced regarding to the snowmelt and evapotranspiration (ET) calculation. The calibration period was set as 1988–1996, and the validation period was set as 1997–2006. We validated the model using observed runoff and gross ecosystem productivity (GEP) and ET production of moderate resolution imaging spectroradiometer (MODIS) in the calibration and validation periods, respectively. Important findings There was a good performance of our application of the WaSSI-C model in the study area. The R2 of calibration period and NS for the total runoff of the study watershed were 0.86 and 0.82, respectively, and 0.78 and 0.67, respectively, for the validation period. Moreover, the R2 of the GEP and ET were 0.89 and 0.78, respectively. We discussed the modeling process and results, and the future direction of improvements of the ET calculation in the end.