Recent progress in land surface models related to the hydrological cycle

What is the difference between a hydrologic model and a land surface model (LSM)? While hydrologic models concentrate on water fluxes and stores, LSMs describe the coupled energy, water and carbon cycles. There are also little conceptual LSMs so that they can best be compared to so-called process-based hydrologic models. Quite a few of the LSMs were developed as part of Earth System Models. Their primary output variables are hence the exchange fluxes with the atmosphere and they are often operated on continental to global scale, which implies very coarse spatial resolutions compared to hydrologic models.

Here I will describe how state-of-the-art LSMs describe the water fluxes and how the fluxes are evaluated. I will outline current developments in the LSM community, focusing on the developments related to the hydrologic cycle. I will discuss current trends amongst developers of LSMs and problems that originate from these trends. I will also point to the challenges that come from ever increasing model resolutions. I will discuss in this context the scaling issue of, for example, soil parameters and how specific choices lead to problems in other parts of the LSM.