New Mexico’s monsoon season runs from mid-June to mid-Sept, it can vary from very little precipitation, leading to large fires, or too much precipitation, like this July, resulting in flash flooding. The National Weather Service has had to put out more than 400 flood advisories for northern and central New Mexico since January; 300 in July alone.
On a drive, out to capture storm/lightning pictures in northern NM, my husband and I came across this massive flash flood. Just before seeing this, on the side of the road, we experienced a down pour with hail. We had to slow down to 25 mph just to be safe (speed limit was 55mph). I, of course, got out of the car, with rain still falling and lightning in the distance, to share this amazing power! This is NOT a river. It is an arroyo that became a river for a brief time joining further south with the Rio Ojo Caliente; we came back to this spot an hour later and it was back to sand.
In desert areas, like NM, flash floods* can be particularly deadly for numerous reasons. Storms in arid regions are infrequent, but they can deliver an enormous amount of water in a very short time; especially during monsoon season. These rains often fall on poorly-absorbent and often clay-like soil, which greatly increase the amount of runoff that rivers and other water channels have to handle. These regions tend not to have the infrastructure that wetter regions have to divert water from structures and roads, such as storm drains, culverts, and retention basins. In some areas, like in the photos, desert roads frequently cross dry river and creek beds (arroyos) without bridges.
Further south on US 285 and SR 111, this same arroyo had flooded over the road causing people to wait to get to their homes. I spoke with a gentlemen who said that he had seen flooding over the road before but never like this. He wasn’t sure if the road was still there.