On the Uncertainties of Projected Future Changes in Land Surface Energy and Water Budgets due to Different Land Surface Schemes and Dynamic Vegetation Impacts

Abstract:

Assessing and quantifying the uncertainties in projected future changes of energy and water budgets over land surface are important steps towards improving our confidence in climate change projections. In this study, the inter-model variation of projected future changes of land surface energy and water fluxes are assessed, using the 2081-2100 and 1981-2000 periods under the Representative Concentration Pathway 8.5 (RCP8.5) for comparison. Also investigated is the influence of dynamic vegetation on amplifying or moderating the uncertainties due to model dependency. Simulation results for surface sensible heat fluxes show a high degree of model dependency mainly in Central Asia, central North America, eastern South America and Central Africa. These uncertainties are further amplified by dynamic vegetation feedback. Although precipitation is very likely to increase in the high latitudes of the Northern Hemisphere, a high degree of model-related uncertainty exists for ET, soil water content and surface runoff, suggesting the discrepancy of land surface models in simulating the water cycles there. Large model-related uncertainties for the surface water budget also exist in the Tropics including southeastern South America and Central Africa. In the high latitudes of the Northern Hemisphere, vegetation dynamics contributes additional uncertainties for the simulated future changes of water cycles in northwestern North America and central North Asia where the projected vegetation changes are uncertain. In the tropics, while the vegetation dynamics adds more uncertainties for the simulated future changes of soil water content in the Amazon and Congo Basins where there exists dense vegetation, it does so for the projected ET changes in the central and southeastern part of South America and the areas north and south of the Congo Basin. Results show that the range of uncertainties for projected future changes of water budget in the high latitudes of Northern Hemisphere is reduced using the same land surface model. It also shows that large ranges of uncertainties for projected future changes of water and energy cycles in response to the simulated vegetation changes exists in the central part of North Asia.