The societal benefits of numerical weather prediction (NWP) forecasts are most evident in populated areas. An urban representation within NWP models should provide improved forecast accuracy. Here, we present the preliminary implementation of an urban scheme within the Integrated Forecasting System (IFS) using a simplified single-layer urban canopy model. The scheme makes assumptions of canyon geometry and considers fluxes from roads, walls, and roofs. Temperature observations were used to optimize single-column model (SCM) parameters using the Gauss-Newton method. Observation comparisons over six European cities, show a 2-m temperature root-mean-squared error reduction from 1.85 to 1.75 K with the urban scheme. Optimized parameters were used globally at kilometric scale in a land surface model. A sensitivity experiment assuming a 100% urban world showed spatially averaged northern hemisphere 2-m temperatures increased by 0.54 K (January) and 0.42 K (July) at night caused by changes in the albedo, emissivity, roughness, and thermal and hydrological properties. Global ∼1-km resolution simulations using ancillary urban mapping information produce an urban heat island effect over major and minor conurbations. Only major conurbations were well represented at ∼9-km resolution. Results from SCM simulations show a heightening of the planetary boundary layer over city sites, with the largest enhancements occurring at night in July (84 ± 48 m) caused by an increased sensible heat flux. These initial developments show the importance of a high-resolution urban representation within NWP models. Improved parameterization and mapping will enable an online representation of energy, water, and trace gas fluxes over residential areas.

中文翻译：

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ECMWF综合预报系统的城市方案：单列和全球离线应用

数值天气预报 (NWP) 预报的社会效益在人口稠密地区最为明显。NWP 模型中的城市表示应提供更高的预测准确性。在这里，我们使用简化的单层城市冠层模型在综合预测系统 (IFS) 中初步实施城市计划。该方案对峡谷几何形状进行了假设，并考虑了来自道路、墙壁和屋顶的通量。使用高斯-牛顿方法，使用温度观测来优化单柱模型 (SCM) 参数。对六个欧洲城市的观察比较显示，使用城市方案可将 2 米的温度均方根误差从 1.85 K 降低到 1.75 K。在陆地表面模型中，在公里范围内全局使用了优化参数。假设 100% 城市世界的敏感性实验表明，由于反照率、发射率、粗糙度以及热和水文特性的变化，北半球 2 米的空间平均温度在夜间增加了 0.54 K（1 月）和 0.42 K（7 月）。使用辅助城市地图信息的全球~1 公里分辨率模拟在主要和次要城市群上产生城市热岛效应。只有主要的大都市在 ~9 公里的分辨率下得到了很好的代表。SCM 模拟的结果显示城市站点上的行星边界层升高，最大的增强发生在 7 月的夜间 (84 ± 48 m)，这是由显热通量增加引起的。这些最初的发展表明了 NWP 模型中高分辨率城市表征的重要性。