2.6.1.6 Prediction

Summary

This section presents the predictive posterior distribution for each hydrological response variable. To guide the interpretation of the results, Table 7 summarises the location and catchment area of each model node.

As described in the uncertainty analysis (refer to Section 2.6.1.5), the maximum raw change (amax), maximum percent change (pmax) and year of maximum change (tmax) reported here are for the hydrological response variables for streamflow: annual flow (AF), interquartile range (IQR), daily streamflow at the 99th percentile (P99), number of flood (high-flow) days (FD), number of low-flow days (LFD), number of low-flow spells (LFS), longest low-flow spell (LLFS) and zero-flow days (ZFD).

The change in surface hydrology predicted due to the additional coal resource development in absolute terms is predicted to have a median decrease of less than 0.01 GL/y, which corresponds to a change of about 0.01%. These changes are several orders of magnitude smaller than the observed mean streamflow (Table 26, Section 2.1.4.1 of companion product 2.1-2.2 for the Clarence-Moreton bioregion (Raiber et al., 2016)). Their effect on mean and high-streamflow hydrological response variables will therefore be minimal. Even the effect on low-streamflow hydrological response variables will be very small, especially in the perennial streams.

The maximum change in surface water – groundwater flux simulated by the groundwater model is several orders of magnitude less than the observed or simulated historical streamflow. The simulated increases in low-flow metrics are considered to be an erroneous overestimate due to artefacts in the simulation of low flow and the definition of the hydrological response variables. Accurately measuring and simulating low-flow conditions is very challenging and requires further efforts.