Robock_Pub_19 Robock, Alan, C. Adam Schlosser, Konstantin Ya. Vinnikov, Suxia Liu, and Nina A. Speranskaya, 1995: Validation of humidity, moisture fluxes, and soil moisture in GCMS: Report of AMIP Diagnostic Subproject 11, Part 1 - Soil moisture. Proceedings of the First International AMIP Scientific Conference, WCRP-92, WMO/TD-No. 732, W. L. Gates, Ed., (World Climate Research Programme, Geneva), 85-90.


We compared model-generated "data sets" and simulations of soil moisture by the AMIP climate models with more than 200 observations taken in the former Soviet Union for 1979-1985, the People’s Republic of China for 1981-1991, Illinois for 1983-present The spatial patterns, mean annual cycles and interannual variations were compared to plant available soil moisture in the upper 1 m of soil.
The "data sets" of Mintz and Serafini and Schemm et al. and the AMIP model output are quite different from the observations. The "data sets" were quite different from each other in many regions, even though they use the same calculation method. The model simulations were also quite different from each other, especially in the tropics. The actual quantities supplied to PCMDI as "soil moisture" are described. In the case of models that do not explicitly consider available soil moisture in the top 1 m, various quantities from various layers were provided. Models with 15-cm field capacities did not capture the large high latitude values of soil moisture. In addition, none of the models properly simulate winter soil moisture variations in high latitudes. They all keep soil moisture constant when the temperature is below freezing, while observations show that soil moisture varies in the winter as much as in other seasons. The observed interannual variations of soil moisture were not captured by any of the AMIP models. Several models have large soil moisture trends during the first year or two of the AMIP simulations, with potentially large impacts on global hydrological cycle trends and on other climate elements. This is because the simulations were begun without spinning up the soil moisture to the model climatology. The length of time it took for each to reach equilibrium depended on the particular parameterization. Although observed temporal autocorrelation time scales are a few months, some models had much longer time scales than that. In particular, the 3 models based on SiB had severe trends in some regions for virtually the entire AMIP simulation period.
It was not possible to calculate complete water budgets due to the design of AMIP Standard History output collection. For AMIP II we recommend that runoff be collected; that instantaneous soil moisture and snow depth (water equivalent) at the end of the month be collected, as these are moisture reservoirs, not fluxes; and that available soil moisture in the top 1 m be specified as the soil moisture parameter.

Prepared by Alan Robock ( ) - Last updated on February 2, 1999