Climate and Terrain - Attribute Uncertainty

A similar assessment of version 3 of the DEM has not yet been undertaken but errors are probably of a similar magnitude. A comparison of derived catchment areas provides a guide to the accuracy of surface drainage pathways and catchment boundaries. Catchment areas computed from the DEM were found to be different from those derived independently for 328 stream gauging stations compiled for the NLWRA[2] by less than 2.5% on average with more than one third of values differing by less than 1%. For 11 gauging stations, catchment area differed by more than 10% up to a maximum value of 29%.

Climate estimates are derived from long-term monthly mean climate surfaces with relative standard errors of about 10% for rainfall and radiation and 0.2 to 0.4 degrees C for maximum and minimum temperature[1]. Errors in elevation values from the DEM also affect climate estimates. The rainfall erosivity has a quoted relative error of approximately 20%[3].

Errors and uncertainty from a range of sources, including that associated with the specification of soil parameters, the annual climate surface coefficients and elevation errors, affect the accumulated soil water surplus used to represent run-off. The water balance model employed is a gross simplification of the processes of run-off generation. In particular, the aggregation of individual rainfall events to a weekly time step will influence the predicted surplus. The accumulated soil water surplus provides an estimate of the potential volume of water that may be available for stream flow. However, many other factors not considered here including wetland or groundwater storage and transmission losses, will influence measured discharge. Nevertheless, Stein (in prep.) found the simple water balance provided a reasonable estimate of the regional scale water balance when compared with measured discharge for about 330 stream gauging stations with unimpaired flow and catchment areas up to 2000 km² compiled for the NLWRA by Peel et al. (2000)[2].

References

1. ^ a b Hutchinson, MF, Houlder, DJ, Nix, HA & and Mcmahon, JP (2000), ANUCLIM Users Guide Version 5.1., Australian National University, Centre for Resource and Environmental Studies, Canberra.
2. ^ a b Peel, MC, Chiew, FHS, Western, AW & McMahon, TA (2000), Extension of unimpaired monthly streamflow data and regionalisation of parameter values to estimate streamflow in ungauged catchments. [online], Report prepared for the National Land and Water Resources Audit. Available at: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.726.9527&rep=rep1&type=pdf.
3. ^ Rainfall erosivity (R factor) (2000), National Land and Water Resources Audit, Canberra, ACT.

Last updated: 22 March 2013