Lewis Fry Richardson: Pioneer Soil Physicist.

Lewis Fry Richardson (1881-1953) was an English polymath who made important contributions to many fields including numerical weather prediction, finite difference solution of partial differential equations, turbulent flow and diffusion, fractals, and the causes of war. During World War I he invented the field of numerical weather prediction, although his methods were not successfully applied until 1950, after the invention of fast digital computers. In 1922 he published his work as the book “Numerical weather prediction”, of which few copies were sold and even fewer were read until the 1950s. To model heat and mass transfer in the atmosphere he did much original work on turbulent flow, and defined what is now known as the Richardson number. His technique for improving the convergence of a finite difference calculation is known as Richardson extrapolation, and was used by John Philip in his 1957 semi-analytical solution of the Richards equation for water movement in unsaturated soil.

Richardson’s first published papers in 1908 concerned the numerical solution of the free surface problem of unconfined flow of water in saturated soil, arising in the design of drain spacing in peat. Later, for the lower boundary of his atmospheric model he needed to understand the movement of heat, water and water vapour in what is now called the vadose zone and the soil plant atmosphere system, and to model coupled transfer of heat and flow of water in unsaturated soil. Finding little previous work on this, he derived partial differential equations for transient, vertical flow of liquid water and transfer of heat and water vapour. He paid considerable attention to the balances of water and energy at the soil-atmosphere and plant-atmosphere interfaces, making use of the concept of transfer resistance introduced earlier by Brown and Escombe (1900) for leaf-atmosphere interfaces. He incorporated finite difference versions of all equations into his numerical weather forecasting model. From 1916, Richardson drove an ambulance in France in World War I, did weather computations in his spare time, and wrote a draft of his book.

Later researchers such as L.A. Richards, D.A. de Vries and J.R. Philip from the 1930s to the 1950s were unaware that Richardson had anticipated many of their ideas on soil liquid water, heat, water vapour, and the soil-plant-atmosphere system.  In particular, the Richards (1931) equation should rightly be called the Richardson (1922) equation!