HR: 10:20h
AN: H11H-01    [PDF]
TI: Demonstrating the Importance of \lq\lq Good" Models of Land Surface Hydrological Processes
AU: Pitman, A
EM: apitman@penman.es.mq.edu.au
AF: Physical Geography, Macquarie University, North Ryde, NSW 2109 Australia
AU: Irannejad, P
EM: pix@ansto.gov.au
AF: ANSTO Environment, PMB 1, Menai, NSW 2234 Australia
AU: McGuffie, K
EM: kendal.mcguffie@uts.edu.au
AF: Applied Physics, University of Technology, Sydney, Broadway, NSW 2007 Australia
AU: * Henderson-Sellers, A
EM: ahssec@ansto.gov.au
AF: ANSTO Environment, PMB 1, Menai, NSW 2234 Australia
AB: To reduce the uncertainty in the prediction of land surface climates,, the Atmospheric Model Intercomparison Project (AMIP) Diagnostic Subproject 12 (DSP 12) and the Project for Intercomparison of Land-surface Parameterisation Schemes (PILPS) have analysed dependence of climate simulations on the land-surface schemes (LSSs). This analysis has comprised three efforts: (i) proving that LSSs matter in coupled simulations; (ii) investigating whether improvements in LSSs have occurred over time; and (iii) searching for novel means of validating LSS predictions. In the first, Irannejad {\it et al.} (2003) introduce a novel method for evaluating the dependence of 19 AMIP AGCMs' LH on the LSS by excluding the impact of the atmosphere. Pseudo LSSs (PLSSs) for LH in the form of multi-variable linear models expressing mean monthly LH as a function of atmospheric forcing are developed. Analysis over three large and climatically diverse river basins shows estimates of mean annual LH from the PLSSs agreeing well with the AGCMs' simulations. RMS errors range from 0.4 to 2.2 W m$^{-2}$ depending on the region and the AGCM. When the PLSSs are driven by single atmospheric forcings, different LSSs behave differently, and the variability of mean annual LH among AGCMs increases. The second strand of our investigation uncovered a clear generational sequence of land-surface schemes: first generation 'no canopy'; second generation \lq SiBlings'; and \lq recent schemes'. We conclude that although continental surface modelling has improved over the last 30 years, full confidence remains elusive, in part due to tuning to available observations. Finally, we show that stable water isotopes challenge predictions of evaporation and condensation processes. These three-pronged findings prove that LSSs are important to AGCM and coupled climate predictions; demonstrate that new, or changed, land-surface components increase diversity among simulations; underline the need for validation data and also challenge current parameterisations with novel observations.
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
SC: Hydrology [H]
MN: 2003 Fall Meeting