Increasing Arabian Peninsula Summer Surface Air Temperature Response to Greenhouse Warming: The Role of Water Vapor Feedback

Interannual variability and trend of summer (June-July-August: JJA) surface air-temperature (SAT) over the Arabian Peninsula (AP) referred to as AP-SAT hereafter, is investigated using observations for the period of 1948-2017. The observed JJA AP-SAT showed a significant positive increasing trend (0.60 °C/decade), with continuous hottest years appearing in 21^st century except 1998. The increasing trends in JJA AP-SAT remain robust and statistically significant in future scenarios too. Here, we use observation to show the proximate factors of the continuously increasing JJA AP-SAT; 1) JJA AP-SAT is strongly connected to the equatorial Indian Ocean, which has been warming continuously during past century, 2) the warming of the surrounding water bodies enhances evaporation and changes the circulation that bring more moisture, 3) the supplement water vapor enhances the green house effect and as a result heat retained at the surface mainly in the south (west to east) of the AP, 4) the central and northern regions experiences sinking motion and clear sky conditions and high solar radiation. The coupled general circulation models of the Climate Model Intercomparison Project phase 5 (CMIP5) framework; with gradual increase in the atmospheric CO2 concentration (1% per year) mimic the observation, showing an increase in the land-sea thermal contrast and resultant circulation changes that are strongly coupled and interactive. This study identified the role of the positive water vapor feedback in enhancing the land surface warming of the Arabian Peninsula.