Parameterization of mires in a numerical weather prediction model

Mires (peat-accumulating wetlands) occupy 8.1% of Russian territory and are especially numerous in the western Siberian Lowlands, where they can significantly modify atmospheric heat and water balances. They also influence air temperatures and humidity in the boundary layers closest to the earth's surface. The purpose of our study was to incorporate the influence of mires into the SL-AV numerical weather prediction model, which is used operationally in the Hydrometeorological Center of Russia. This was done by adjusting the multilayer soil component (by modifying the peat thermal conductivity in the heat diffusion equation and reformulating the lower boundary condition for Richard's equation), and reformulating both the evapotranspiration and runoff from mires. When evaporation from mires was incorporated into the SL-AV model, the latent heat flux in the areas dominated by mires increased strongly, resulting in surface cooling and hence reductions in the sensible heat flux and outgoing terrestrial long-wave radiation. Presented results show that including mires significantly decreased the bias and RMSE of predictions of temperature and relative humidity 2 m above the ground for lead times of 12, 36, and 60 h from 00 h Coordinated Universal Time (evening conditions), but did not eliminate the bias in forecasts for lead times of 24, 48, and 72 h (morning conditions) in Siberia. Different parameterizations of mire evapotranspiration are also compared.