Improvement of WRF/Noah Simulations for the Fergana Basin in Central Asia Based on Irrigation Schemes and Soil Data Update

This study aims to identify the improvements of WRF/Noah simulations for the Fergana basin in central Asia resulting from the implementation of an irrigation scheme and update of soil data in climate simulations for the period of 2007–2011. First, simulations with the WRF/Noah model within which an irrigation scheme was implemented were compared with those involving the default WRF/Noah model. The results indicated that the irrigation enhanced soil moisture and thus intensified evapotranspiration and latent heat and reduced sensible heat; under these conditions, cooling and wetting effects occurred on surface air. The warming and drying biases were partly corrected. The root mean squared error (RMSE) of air temperature at 2 m decreased from 6.52°C to 5.81°C. Meanwhile, the RMSE of the specific humidity of air at 2 m decreased from 1.66 g/kg to 1.13 g/kg. Second, on the basis of the implemented irrigation scheme, the soil texture and hydraulic parameters were updated with the data from the International Soil Reference and Information Centre. Clay and loam were replaced with silty clay loam and silty loam for the plain area of the Fergana basin. Hence, the wilting point declined, and the amount of available water in the soil increased. The bias of the water demand of the simulated irrigation was partly corrected. Moreover, the evapotranspiration and latent heat intensified, and the sensible heat decreased. Hence, intensified cooling and wetting effects were observed on surface air. The warming and drying biases were corrected further. Under these conditions, the RMSE of air temperature at 2 m decreased from 5.81°C to 5.46°C whereas, that of the specific humidity of air at 2 m decreased from 1.13 g/kg to 1.08 g/kg. These findings suggest that implementing an irrigation scheme and updating soil data may improve the performance of the WRF/Noah model for the Fergana basin in central Asia.