A tale of two droughts: the effects of temperature on recent southwestern droughts

Multi-year and multi-decade drought is a part of the history of climatic variability in the southwestern United States. Major drought episodes in the instrumental record include 1897-1904, 1947-1956, and 1999-present. These droughts each have common features, but somewhat distinctive spatial and temporal characteristics. The 1950s drought was one of the most severe and extensive in the Southwest in the last one hundred years. However the economic, ecological and hydrologic impacts of the recent drought may soon supplant it. Recent studies suggest that rising temperatures are linked to more severe drought. This study compares some causes and effects of the 1947-1956 drought with the current drought in the White Mountain and Mogollon Rim area along the Arizona-New Mexico border. This area is agriculturally and economically important, has no large cities to cause heat island effects, and is inhabited by a diverse population with a range of livelihoods, ethnic backgrounds, and vulnerability to drought.

There are clear differences between the two droughts. The 1947-1956 drought was relatively cool, with maximum and minimum November-April temperatures 0.9°C cooler than those observed between 1999 and 2004. Increased winter air temperature during the winter can reduce snowpack and cause earlier snowmelt, exacerbating the problem of low precipitation. While both droughts had low winter precipitation, snowpack was consistently lower in during the most recent drought, with 1999-2002 experiencing some of the lowest snow levels of the last sixty years. The 1947-1956 drought was also marked by a period of below-average summer precipitation in addition to the winter drought. Despite the slightly wetter summers, the recent drought resulted in more widespread loss of woody vegetation – due, in part, to enhancement evaporation rates, plant stress, and increased reproduction of destructive insects, such as the bark beetles.

If temperatures continue to increase, these effects could have profound economic and social impacts in this region, where a significant portion of the local economy is dependent on the ski industry, tourism, and forest-products industries.