The bulk of the rain came down Tuesday in what Al Jazeera called “only two sets of 15-minute heavy rainfalls.” The pair of swift deluges overwhelmed the sandy ground’s ability to soak up water, causing it to funnel into roadways that quickly became rivers.

Part of what made the city so vulnerable to flooding amid seemingly less-than-impressive rain amounts is its location in the Zagros foothills. That makes it susceptible to channeling effects in rivers and valleys, reminiscent of the scenes that unfolded in Ellicott City, Md., in May.

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At least 23 have been reported dead, with more than 200 injured. After rounds of morning rain, drier air and sunshine will overspread the beleaguered region this afternoon, affording an opportunity to survey the damage and begin recovery.

According to the Jerusalem Post, thousands have been relocated to emergency shelters provided by the government, displaced as the floodwaters slowly recede. A number of at-risk dams also pose a downstream flood hazard.

The rains behind Shiraz’s flooding weren’t relegated to Iran’s south. Flood concerns first arose last week as moisture-loaded storms targeted northern regions on the shores of the Caspian Sea.

Most places in Iran average about 10 inches of rain or less per year. That scant precipitation classifies a large chunk of the nation as “semidesert.” While verdant forests and lush woodlands blanket the more humid northern stretches bordering the Caspian Sea, the vegetation drops off the farther south. When water comes down as bountifully as it did Tuesday, communities aren’t always prepared.

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The Yasoge weather station, about 90 miles northwest of Shiraz in the town of Yasuj, picked up 0.44 inches Monday — noteworthy on its own but dwarfed by the nearly half a foot of water that dropped Tuesday. That’s more than the mean rainfall for February and March combined in Washington.

Khorramabad, in west-central Iran, got its heavy rainfall Monday with 3.07 inches, followed by 0.8 inches Tuesday. Meanwhile, Gach Saran Du Gunbadan’s weather station didn’t see a drop of water Monday but was soaked with 3.20 inches Tuesday.

Iran’s capital, Tehran, is dealing with floods creeping in on the city’s east side, although downtown should probably escape unscathed. Just under three-quarters of an inch was measured through Tuesday afternoon.

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The highly variable day-to-day distribution of rainfall is characteristic of convective environments. Scattered slow-moving heavy showers or thunderstorms deliver feast-or-famine rainfall totals — a regime in which training or stalled storms can rapidly spell disaster. Towering storm tops are visible in satellite shots, while water vapor imagery shows the violent clash between dry and moist air.