Novel physical and numerical methods for simulating water and heat transfer in land surface models.

改进陆地水循环的陆地表面模型对于在气候变化中提供更好的预报至关重要，例如在洪水预报中。陆地表面模型，如UKMO的联合英国陆地环境模拟器（JULES），通过理查兹一维偏微分方程（PDE）的数值形式描述土壤中的非饱和流动。这种高度非线性方程的解不可避免地导致数值和精度问题，从而影响其水文性能。最近的注意力集中在采用新的水文模型方法上。本项目涉及两种最新的一维非饱和区流动求解方法（Ogden et al., 2015; Lee, Baines and Langdon, 2015）在JULES中的实现和测试。这两种方法都使用基于速度的偏微分方程来表示含水量的深度，奥格登方法通过链图变换，贝恩方法通过局部质量守恒。（不同的）pde使用显式方案在时间上向前推进。奥格登土壤水分速度方程（SMVE）方法已经应用于土壤水分的三种输送模式，即入渗、与地表分离的湿润锋和地下水补给。贝恩斯方法（CMF）有待开发。学生将扩展这两种方法来解释热流。该奖学金提供了将计算建模应用于高度重要的实际问题的机会，并将包括访问UKMO。智力上的挑战将是推导出一种一致的方法来耦合土壤中的水和热传输。

Improved land surface modelling for the terrestrial water cycle is critical for providing better forecasts within a changing climate, for example in flood prediction. Land surface models, such as UKMO's Joint UK Land Environment Simulator (JULES), describe unsaturated flow in soils through a numerical form of the Richards one-dimensional partial differential equation (PDE). Such a solution to a highly non-linear equation inevitably leads to numerical and accuracy issues, which impact on their hydrological performance. Recent attention has focussed on adopting novel approaches to hydrological models.This project concerns the implementation and testing of two recent 1-D unsaturated zone flow solution methods (Ogden et al., 2015; Lee, Baines and Langdon, 2015) into JULES. Both methods use a velocity-based PDE for the depth in terms of the water content, the Ogden approach through a hodograph transformation, the Baines approach through local mass conservation. The (different) PDEs are stepped forward in time using an explicit scheme.The Ogden Soil Moisture Velocity Equation (SMVE) method has already been applied to the transport of three regimes of soil moisture, namely infiltration, wetting fronts disconnected from the surface, and groundwater recharge. The Baines approach (CMF) awaits development.The student will extend both approaches to account for heat flow.The studentship affords the opportunity to apply computational modelling to a real problem of high importance, and will include visits to the UKMO.The intellectual challenge will be to derive a consistent method for coupling water and heat transport within the soil.