The consequences of climate change are complex, far-reaching, and are felt on global and regional scales. Climate projections on regional and local scales are essential for adaptation and planning on national and sub-national levels to increase resilience and robustness of industrial and social infrastructures. Adaptation on a regional scale is more feasible than on a global one, as proposed global geoengineering "solutions" such as solar radiation management could assure the planet cooling but cause adverse regional consequences. The MENA climate is especially vulnerable to these adverse effects. Freshwater is the most vital resource in the desert environment. Management of water resources over MENA is challenging. Population growth, industries, and agricultural activities over the past century have led to an increase in demand for water supply. At the same time due to environmental conditions, per-capita freshwater consumption is high. For example, the Kingdom of Saudi Arabia (KSA) has one of the highest per-capita rates of water consumption (near 300t yr-1) in the world. The KSA desalinizes about 1Gt of water per year producing 25-30% of all desalinated water in the world. Precipitation Modification The idea of artificially increasing the precipitation has attracted attention for many years. The United Arab Emirates are currently funding research on a rain enhancement program that explores different technical options. There were marginally successful attempts using cloud seeding to trigger rain processes in desert environments. The ways in which dusts can affect clouds and precipitation is not widely known or fully understood. Afforestation is a known way of increasing precipitation. Instead, we found that decreasing surface albedo by distributing solar panels over the Red Sea coastal plain enhances sea breezes and triggers more precipitation over that region. This method has little environmental consequence in the surrounding areas. It can be used as a climate adaptation measure and is an example of regional-scale precipitation geoengineering. Temperature trend The Middle East experiences an enhanced level of warming in comparison with the average warming trend over the Northern Hemisphere. One of the reasons is extreme dryness of the region that prevents the land surface energy balance adjustment by increasing evaporation. Therefore, the desert temperature sensitivity to radiative forcing, solar and longwave, is higher than that averaged over the global landmasses. The highest warming trend is observed in Summer making temperature extremes more severe. Fig. 1 shows the temperature projection in MENA until 2050 for two IPCC emission scenarios RCP8.5 (red, business as usual) and RCP4.5 (blue) with decreasing of CO2 emissions starting from 2030. This assessment was conducted for the UN ESCWA project on water resources and social vulnerability in Arab countries. The projections were calculated on a KAUST supercomputer using the global high-resolution atmospheric model (HiRAM) with a regional spatial resolution of 25x25 km2. The results show steady warming for more than 1 K by the middle of the 21st century. Regional climate predictions Regional climate changes are driven by global climate trends. But predicting regional climate is more challenging than the global climate, as high spatial resolution is required, and natural variability, nonlinear circulation responses, and local physical effects complicate the analysis. Professor Stenchikov's group at KAUST is focusing on the MENA region that is one of the most vulnerable to climate change. The MENA environmental characteristics are at the brink of livability, but global warming will be exacerbating impacts on health, infrastructure, human migration, biodiversity, tourism, and food production. The current regional climate prediction technology is based on two pillars: Simulations with fine-resolution global models and downscaling Earth System Model outputs using nested regional models. The technology we are developing at KAUST is based on a combination of these two approaches, as we conduct a deep downscaling of the high-resolution global climate forecast using the regional atmospheric model. To add in physical consistency, we coupled the regional atmospheric model with the regional ocean model accounting for aerosol and atmospheric chemistry processes. Global dust emissions Along with Central and Eastern Asia, the MENA significantly contributes to global dust emissions, which are in the range of 1000–2000 Tg yr-1. MENA accounts for more than half of global dust emissions. Dust affects solar and terrestrial radiation, the planetary energy balance, atmospheric circulation. Dust produces the world's largest solar radiative cooling reaching in the southern Red Sea 60 W/m2. The prolonged dryness and social conflicts led to the growth of dust aerosol optical depth (AOD) that characterizes the radiative effect of aerosols (see Fig. 2). Dust deposition on the surfaces of solar panels inhibits their efficiency. However, absorption of UV radiation by dust diminishes the effect of UV on humans. Dust radiative effect is complex as dust particles both reflect and absorb solar radiation, and generate a significant greenhouse warming. As a result, dust cools the surface but warms the atmosphere. The radiative effect of dust depends on the surface albedo and solar zenith angle. Atmospheric heating caused by Saharan dust alters both Hadley and Walker circulation moving the rain belt north in Summer increasing precipitation in Sahel. We found that the radiative cooling of the Southern Red Sea due to accumulated dust layers affects circulation and energy balance of the sea, the effect that was not previously recognized. Dust is not the only aerosol in the Middle East. Anthropogenic aerosols are produced as a result of industrial activity, traffic, power generation are abundant, especially in the population centers. The aerosol's mix, so cold particulate matter (PM) severely affects air quality. The dramatic increase in the level of air pollution in developing countries over the last decades is forced by rapid economic and population growth, burning of fossil fuels, construction and agricultural activities. Still, the primary cause of air pollution in the MENA is mineral dust, and it is on the rise (see Fig. 2). In KSA dust is responsible for about 95% of aerosol concentration. But in the cities, an anthropogenic aerosol component is coming on the top of dust significantly deteriorating the urban air quality. At almost all territory of the Arabian Peninsula PM pollution exceeds the World Health Organization (WHO) limits. Climate models allow us to understand the physical mechanisms of climate variability and estimate future climate changes. But models alone are not sufficient to make reliable estimates. The model parameter identification and testing require accurate observations of environmental characteristics, especially, associated with aerosols. KAUST Dust monitoring Professor Stenchikov has established a comprehensive aerosol monitoring research at KAUST campus. The KAUST AERONET site has been operational for almost a decade providing multi-wavelength observations of column integrated aerosol optical depth, aerosol size distribution, Angstrom exponent, and refractive index. A micro-pulse lidar measures vertical distribution of aerosol backscattering coefficient. We developed a new retrieval algorithm that allowed us to obtain vertical distribution of aerosol extinction, single scattering albedo, and aerosol mixing ratio. We were the first who conducted systematic measurements of aerosol optical depth over the Rea Sea using a hand-held sunphotometer (MICROTOPS). These measurements are conducted in cooperation with the NASA Goddard Space Flight Center and observations are accessible at the NASA website within AERONET, MPLnet, and MARITIME archives. We also conducted a multi-year campaign on measuring aerosol deposition rate and conducted mineralogical and size distribution analysis of deposition samples. This is meant to help predict the dust health effect, its radiative properties, and provide the means to test dust mass balance. The combination of advanced modeling with the integrated results of environmental monitoring is a proven approach to advance regional climate forecast for MENA to inform environmental decision-making. There is a lot that must be understood regarding the effect of dust in the desert environment. For example, dust chemically and microphysically interacts with anthropogenic pollutants e.g. sulphate aerosols, that changes dust radiative effect and life cycle. The comprehensive climate models allow integrating empirical data with physical mechanisms and are invaluable for understanding complex climate processes. These models could be used for assessment of the efficacy of adaptation and mitigation measures, and are instrumental in evaluating and mapping renewable energy resources. [email protected] — The writer is the Chair of Earth Sciences and Engineering Program at King Abdullah University of Science and Technology (KAUST).
