When cities get in the way of nature's path

The science behind the rainfall is explained and how it affects the ecosystem in the UAE.

Heavy rain washes dust from the air, refreshes desert plants and replenishes underground water supplies. But in a city, dense building blocks prevent this natural cycle and can increase pollution in the sea. "The main benefit of rain is a recharge to the groundwater," said Dr Sandra Knuteson, the assistant professor of environmental science at the American University of Sharjah. Rain refills aquifers, which are layers of rocks or other material, such as gravel or clay, from which water can be drawn through wells. This water can be used for drinking or agriculture.

From high in the mountains, the water flows down the wadis. "In the mountains, water runs over the rock and down the path of least resistance rather than infiltrating into the solid rock, then accumulates in the wadi and starts flowing fast," Dr Knuteson said. In several areas, such as Hatta, dams have been built in the wadi to help store some of this water. I bet if you went to the Hatta Dam shortly after the rains, it would be extremely full compared to usual."

However, hard surfaces in the city prevent the easy flow of water. "Unfortunately, with all the impervious surfaces in the cities - roofs, sidewalks, roads, parking lots, hard packed sand areas - water does not always infiltrate," she said. The runoff instead "picks up oils and chemicals" from the road, carrying contaminants into the sewer system and out to the sea. While the rain can be destructive, it will lead to the blooming of plant life. Dr Knuteson said that local quick-growing desert plant species would be prompted to germinate and flower. This process had already started due to earlier rains, and many wildflowers had consequently bloomed.

"More should bloom in a few weeks to a month."
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