USE OF MIDLATITUDE SOIL-MOISTURE AND METEOROLOGICAL OBSERVATIONS TO VALIDATE SOIL-MOISTURE SIMULATIONS WITH BIOSPHERE AND BUCKET MODELS

Union at hundreds of stations. In this paper, the authors use data fro m six of these stations from different climatic regimes, along with an cillary meteorological and actinometric data, to demonstrate a method to validate soil moisture simulations with biosphere and bucket models . Some early and current general circulation models (GCMs) use bucket models for soil hydrology calculations. More recently, the Simple Bios phere Model (SiB) was developed to incorporate the effects of vegetati on on fluxes of moisture, momentum, and energy at the earth's surface into soil hydrology models. Until now, the bucket and SiB have been ve rified by comparison with actual soil moisture data only on a limited basis. In this study, a Simplified SiB (SSiB) soil hydrology model and a 15-cm bucket model are forced by observed meteorological and actino metric data every 3 h for 6-yr simulations at the six stations. The mo del calculations of soil moisture are compared to observations of soil moisture, literally ''ground truth,'' snow cover, surface albedo, and net radiation, and with each other. For three of the stations, the SS iB and 15-cm bucket models produce good simulations of seasonal cycles and interannual variations of soil moisture. For the other three stat ions, there are large errors in the simulations by both models. Incons istencies in specification of field capacity may be partly responsible . There is no evidence that the SSiB simulations are superior in simul ating soil moisture variations. In fact, the models are quite similar since SSiB implicitly has a bucket embedded in it. One of the main dif ferences between the models is in the treatment of runoff due to melti ng snow in the spring-SSiB incorrectly puts all the snowmelt into runo ff. While producing similar soil moisture simulations, the models prod uce very different surface latent and sensible heat fluxes. which woul d have large effects on GCM simulations.