Greenhouse-gas induced warming amplification over the Arabian Peninsula with implications for Ethiopian rainfall

Observed surface warming trends over the Arabian Peninsula are a factor of 1.4–2.1 greater than the tropical mean and a factor of 2.3–3.1 greater than the global mean. The primary reason for the amplified warming is the absence of latent cooling over the dry surface, not trends in net longwave heating or solar fluxes. Well-validated regional model simulations with 30-km resolution are used to evaluate the implications of the amplified warming for the regional climate through the twenty-first century. Projected warming rates are similar to the observed ongoing warming, and low-level specific humidity increases by 50% by the end of the century. Precipitation increases occur only in summer in the southwest corner of the peninsula in association with enhanced orographic precipitation. Concurrent evaporation increases ameliorate and can even reverse increases in surface water availability associated with higher rainfall. A strengthening of the low-level negative meridional geopotential height gradient between the Arabian Peninsula and the Horn of Africa strengthens the zonal branch of the Somali jet, increasing westerly moisture transport into the Ethiopian Highlands and enhancing summer rainfall in northern Ethiopia by 20% at mid-century and by 35% by the end of the century. Confidence in the results is supported by the similarity of the projections with observed modes of variability and current trends.