January and July climate simulations over the SADC region using the limited-area model DARLAM

High-resolution climate simulations of near-surface variables are presented for January and July over the Southern African Developing Countries (SADC) region using the CSIRO Division of Atmospheric Research Limited-Area Model (DARLAM) nested within a General Circulation Model (GCM). The model domain includes tropical (north and south of the equator) and subtropical (Southern Africa) regions. Objective measures of skill are used to assess the quality of model simulations, and the performance of the model is verified over various subregions of the model domain. South of the tropics, DARLAM fields are not only superior to those produced by the GCM, but also compare well with mesoscale observations. This is particularly true for the spatial distribution of rainfall and screen temperature simulations. DARLAM, however, severely over-estimates rainfall totals over regions of steep orography. WaterSA Vol.28(4) 2002: 361-37

Climate projections for southern Australian cool-season rainfall: insights from a downscaling comparison

The projected drying of the extra-tropics under a warmer climate has large implications for natural systems and water security in southern Australia. The downscaling of global climate models can provide insight into regional patterns of rainfall change in the mid-latitudes in the typically wetter cool season. The comparison of statistical and dynamical downscaling model outputs reveals regions of consistent potential added value in the climate-change signal over the 21st century that are largely related to finer resolution. These differences include a stronger and more regionalised rainfall decrease on west coasts in response to a shift in westerly circulation and a different response further from the coast where other influences are important. These patterns have a plausible relationship with topography and regional drivers that are not resolved by coarse global models. However, the comparison of statistical and dynamical downscaling reveals where the method and the configuration of each method makes a difference to the projection. This is an important source of uncertainty for regional rainfall projections. In particular, the simulated change in atmospheric circulation over the century is different in the dynamical downscaling compared to the global climate model inputs, related in part to a different response to patterns of surface warming. The dynamical downscaling places the border between regions with rainfall increase and decrease further north in winter and spring compared to the global climate models and therefore has a different rainfall projection for southeast mainland Australia in winter and for Tasmania in spring