Extreme drought can worsen flash flooding during heavy rain

 

Heavy rainfall during drought conditions may not always be a good thing and can actually cause flash flooding to become worse when it occurs. Dallas, Texas went from exceptionally dry (drought) conditions, to the second wettest August on record in a matter of hours as heavy rain fell across central and east Texas late Sunday night and Monday morning. Heavy rain continues to fall south of the Dallas/Ft. Worth area Monday evening, but flooding concerns continue with Flood Watches through Monday evening across Texas, but lasting through Tuesday evening in Louisiana.

Numerous rainfall records were broken in the DFW as the 9.19 inches of rain they received was the second highest 24 hour precipitation event since September 4-5th, 1932, when 9.57 inches of rain fell during that 24 hour period. Significant flooding has taken place not only across the Dallas area, but also in other cities and towns throughout Texas. Heavy rainfall is expected to continue Monday night into Tuesday.

It comes as no surprise that many across the Plains and out West have been baking in the heat as temperatures over the summer months have soared well over 100 degrees, multiple times. The extreme heat and lack of rainfall has only made the drought conditions worse west of the Mississippi River. Nearly the entire state of Texas has been either in the 'extreme' drought or 'exceptional' drought condition category for quite some time. And while the rain they received the last 24 hours will help some, the drought likely made the flash flooding worse in some locations.

Soil that is dry, hard and cracked acts just like a hard surface. So as heavy rain quickly falls on that hard surface, the rain drops tend to 'bounce' off the soil, rather than soaking in. This in turn causes more runoff which only adds to the flooding risk. Areas that are experiencing drought conditions benefit more from a prolonged, soaking rain - one that occurs for a couple of days at a slower and steady pace. While the soil may still be dry, hard and cracked the slow and steady nature of the rain allows the soil to soak in the rain more efficiently. While there may still be some issues with flooding, it typically isn't as extreme or devastating as when it occurs during a heavy rain event.