Abstract
Abstract. Evaluating the models we use in prediction is important as it allows us to identify uncertainties in prediction as well as guiding the priorities for model development. This paper describes a set of benchmark tests that is designed to quantify the performance of the land surface model that is used in the UK Hadley Centre General Circulation Model (JULES: Joint UK Land Environment Simulator). The tests are designed to assess the ability of the model to reproduce the observed fluxes of water and carbon at the global and regional spatial scale, and on a seasonal basis. Five datasets are used to test the model: water and carbon dioxide fluxes from ten FLUXNET sites covering the major global biomes, atmospheric carbon dioxide concentrations at four representative stations from the global network, river flow from seven catchments, the seasonal mean NDVI over the seven catchments and the potential land cover of the globe (after the estimated anthropogenic changes have been removed). The model is run in various configurations and results are compared with the data. A few examples are chosen to demonstrate the importance of using combined use of observations of carbon and water fluxes in essential in order to understand the causes of model errors. The benchmarking approach is suitable for application to other global models.
Highlights
Changes in atmospheric carbon dioxide and water vapour affect the global radiation budget and are important drivers of climate change
We decided to encapsulate the seasonality of the Normalized Difference Vegetation Index (NDVI) and leaf area index (LAI) from the model by looking at the area-average value of the selected river basins
Most of the river basins are fairly uniform in climate and vegetation type, and so this represents a simple way of representing the mean response of the plants to climate in terms of phenology, which allows us to compare the plant response directly to the response of the water balance through the river flow
Summary
Changes in atmospheric carbon dioxide and water vapour affect the global radiation budget and are important drivers of climate change. The water vapour flux from the land to the atmosphere affects the weather patterns of the world. Spatial difference in the water held in the soils and subsequent patterns of seasonal evaporation and plant growth likely affect rainfall (Los et al, 2006). Increases in atmospheric greenhouse gas concentrations are expected to alter rainfall patterns significantly (IPCC, 2007, Fig. TS.30) and understanding the role of the land surface within such change is important. The land surface is expected to play a major and changing role in the global carbon cycle and changes in the land cover due to land used for food and fuel production can have impacts on the weather and climate (Cox et al, 2000)
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