Situated on the rolling prairies of northeast Texas, along the Trinity River, the altitude of Dallas ranges from 137 to 229 meters (450 to 750 feet) above sea level. Historically, the Dallas area has been plagued by floods and drought due to its location in a region between lush and rainy Louisiana and the desert of west Texas; wet and dry years often alternate. Though droughts have hit the city as recently as 1998, city officials combated the flood problem early in the twentieth century by straightening and widening the channel of the Trinity River.

The Trinity River, as many highly trafficked bodies of waters, was polluted for much of the twentieth century, though clean-up efforts and a lessening of water-borne shipping have improved the river's water quality. In 1998 the Environmental Protection Agency (EPA) gave the Dallas watershed a high rating, well above the national average; however, the air quality was not as good, ranking below the national average.

In September 1995, the EPA made Dallas a pilot city for its Brownfields National Partnership grant program. (Brownfields are abandoned and contaminated industrial sites.) The program allotted nearly $53 million towards the cleanup and redevelopment of blighted areas in Dallas.

Dallas has a Sunbelt climate, with hot summers and mild winters. Average highs in July are close to 53°C (96°F), while average lows in January only dip to 19°C (34°F). It rarely snows in Dallas. Annual average rainfall is 81 centimeters (32 inches). Dallas' Sunbelt climate offers an average of 237 sunny days per year.