Maize cropping systems dominate crop land use in Sub-Saharan Africa (SSA), where rainfed agriculture is highly vulnerable to climate variability, exacerbating hunger and poverty. Effective soil water management practices (SWMPs), such as straw mulching, are known to improve water availability and enhance maize productivity. However, limited research studies have focused on straw mulch thicknesses and depth impact on maize rainfed production systems of SSA. This study evaluates the effects of different straw mulch thicknesses (2 cm, 4 cm, and 6 cm) on maize yield simulated using the AquaCrop model under the low (SSP1-2.6) and the high (SSP3-7.0) emission climate change scenarios from the IPCC's selected CMIP6 climate models. Field experiments with varying straw mulch thicknesses (2 cm, 4 cm, and 6 cm) were used to calibrate the AquaCrop model, which was then applied to simulate maize yields across current (2018-2019) and future (2020-2099) periods. Results showed that, straw mulch thickness significantly influences maize yields, with 4 cm and 6 cm treatments increasing maize yield by up to 40 %. The 2 cm mulch, under the high emission scenario, led to a 53 % yield increase, with the 4 cm mulch being identified as the optimal thickness for maximizing yield and water use efficiency (WUE). These findings suggest that straw mulch thickness should be adjusted to regional climatic conditions for optimal effectiveness. This study highlights the importance of integrating SWMPs with climate adaptation strategies to sustain maize productivity and improve food security in the context of climate change.