Global warming likely to mean more droughts and more floods

The gaping hole some 60 feet wide is a unique conduit through the rocky limestone to the Edwards below. It's roughly 290 feet straight down to the fissures and pockets that make up the major water source for Central Texas.

On an overcast day in a record-wet spring that has prompted shrubs and plants to sprout from the normally barren sinkhole walls, water is flowing from Seco Creek into the massive opening. The spray of rushing water abounds and the landscape is lush. Most important, it is wet. Real wet.

But here's the rub. The creek flowing into the sinkhole was dry or nearly so for 14 months before torrential rainfalls this spring. The sinkhole's very name reflects the drought cycle: Seco is Spanish for dry.

As global warming continues to alter the climate, scientists agree that such boom and bust cycles will become more severe. Droughts will become more common as the area's already strained water supplies are further depleted by longer dry spells, evaporation and even the increased thirst of vegetation trying to survive in hotter climes. And the rain that does come is likely to arrive in more violent storms.

"It's paradoxical," said Andrew Dessler, professor at Texas A&M's Department of Atmospheric Sciences. "But you can expect both more drought and more flood."

South Texas' weather always has featured wild swings, especially when it comes to rainfall. San Antonio's average precipitation is more than 32 inches per year, but that average is anything but a norm.

The pattern over the past few years is a good example.

This year has been dominated by deluges that spawned flash floods and claimed 63 lives around the state. But those downpours broke a two-year drought that put San Antonians on harsh water restrictions and dried lawns to a crisp.

The numbers are telling. In 2006, slightly more than 21 inches of rain fell; the year before, about 17 inches fell.