24°34′51″N46°42′47″E / 24.5809°N 46.71311°E /24.5809; 46.71311
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Wadi Hanifa (Arabic:وَادِي حَنِيْفَة,romanized: Wādī Ḥanīfah), historically known asWadi al-Arad,[1] is awadi (seasonal river) in theNajd region,Riyadh Province, in centralSaudi Arabia. The valley runs for a length of 120 km (75 mi) from northwest to southeast, cutting through the city ofRiyadh, the capital of Saudi Arabia. A string of towns and villages lie along the valley, includingUyaynah,Irqah andDiriyah. The historical city of Riyadh itself is on the northeastern side of the wadi, but the city has now expanded across Wadi Hanifa, with the sub-municipalities ofAl-Shifa andAl-Urayja on its southwestern side.
Inancient times, the wadi was known asal-Irdh (العرض). Its current name is derived from that of theBanu Hanifa, the principal Arab tribe in the area at the time of theIslamic conquest of Arabia.
Inpre-historic times, rain fell heavily in the region. This is reflected in the local folk tradition that claims that during the reign of the ancient kingdom ofAl-Yamamah, the area was once covered with oases and fertile farmland.
Temperatures in summer reach an average of 42.9 °C (109.2 °F), and precipitation averages only 60 millimetres (2.4 in) per year in the driest places. Rain falls with great intensity for short periods, causing flash floods. The nature of the dry, warm climate leads to a high percentage of the scarce rainfall being instantly evaporated. That which remains mostly ends up as groundwater. While abundant, the levels of the water table are being tested by the rapid growth the city of Riyadh has seen in the past fifty years, from a population of 150,000 in 1960 to an estimated 5 million today.[citation needed]
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