It has been raining a lot lately in Cairo. The average rainfall in Cairo is one inch a year. Since March, it has rained four times. Yesterday it rained heavily for an hour, with large, round raindrops, which evaporated on the hot concrete. My taxi driver, Emad, remarked yesterday that he does not understand why there is so much rain, but is pleased about it. You can smell the rain when it is on its way in the desert. I grew up in the New Mexico desert, so I know the smell. It is a delicious, earthy, full smell which makes you feel happy and alive.
The desert is blooming. Bougainvillea vines (Bouganvillea glabra), previously merely undistinguished climbers, are exploding in a profusion of pink, magenta, and orange leaves. Jacaranda trees (Lamiales Bignoniaceae, genus Jacaranda) shade the streets with blooms of a deep violet. Cassia trees (Senna bicapsularis or possibly Cassia spectabilis) produce an abundance of golden flowers. Closer to the ground, the grass is a sturdy, intense dark green, shrubs of Lantana (Lantana camara), a hardy dry weather plant favored by goats, is growing wildly in clusters of tangerine and red balls flecked with white. Bright red hibiscus (Hibiscus Rosa-senensis) are coming into their own with showy flowers. The shrubs are thin, and not as abundant in Egypt as in Hawaii, but they do a wonderful job of livening up the gates of my drab monochromatic residential estate of El Rehab.
I wonder if the high amount of rain Cairo is receiving has anything to do with global warming? Geographer David Rutherford, recipient of a one million dollar grant from the National Science Foundation for climate change education notes:
"Global warming produces greater energy in the atmospheric system, and that produces the potential to cause more and stronger weather (weather of all sorts). Also, warmer air holds larger amounts of water, but it also increases the rate of evaporation and transpiration (from plants). Consequently, the actual affects of increasing temperature on rain and weather events is uncertain. In addition, these effects vary from place to place, and the question of whether global warming is causing more or less rain or weather events in any particular place is difficult to determine."
The Saharan climate is fragile and it is volatile. A warmer Africa with very small increases in rainfall could green the Sahara quickly, leading to a virtuous circle of increased rainfall due to more green bio mass. Max Claussen of the Max Planck Institute for Meteorology has looked into this possibility.
Yet, increasing desertification remains a danger for the Sahel and Sahara. If pastoralists drive their herds into greening areas, this could destroy the positive effect increasing vegetation has on the climate. In addition, the southern edge of the Sahara is home to a rapidly burgeoning human population, which is placing severe pressure on waterways such as Lake Chad and the White Nile. According to National Geographic, North Africa is the area of greatest disagreement among climate change modelers.