Calculate soil moisture using daily (or any other scale) precipitation and temperature . Use the Richard's Equation and Darcy's law (Or any theory you like attached to soil moisture content determination ). Don't hesitate to modify the approach to suite your goal (soil moisture or soil water content ). However, modification should be done only if it is required and technically sound .Write a small code for this in C or C++ or Fortran (most preferred) or Matlab ( least preferred ) (with comment will fetch you more points).