New Doubt Cast on Link Between Global Warming and Increased Drought
There have been devastating droughts in the past few years in places like Africa, Australia, and the United States. Last summer, the drought in the central US caused the loss of massive crops and a major economic hit for the country. The seemingly increasing prevalence of droughts has some announcing the effects of climate change coming to fruition. However, a new study from researchers at Princeton University in New Jersey and the Australian National University in Canberra has cast doubt on this premise. Their work indicates that the development of drought is much more complex than formerly believed and that recent droughts were more an aberration than an overall drying trend.
The previous theory states that increased temperature will cause more rapid evaporation, increasing the frequency and severity of drought. The United Nations Intergovernmental Panel on Climate Change (IPCC) has adopted this theory, stating in a 2007 report, "more intense and longer droughts have been observed over wider areas since the 1970s."
"The overall view has been that as temperature increases drought is going to increase," said Justin Sheffield, a research scholar in Princeton's Department of Civil and Environmental Engineering. "But it is not that simple."
Sheffield and his colleagues believe that overestimates of drought worldwide are caused by errors found in a common model used for assessing drought, known as the Palmer Drought Severity Index. The Palmer Index is used for its simplicity, even though better drought models are available.
The Palmer Index was developed in the 1960s to determine levels of federal aid for US farms damaged by drought. The Index relies heavily on temperature, and because of that, it is extremely sensitive to warming. It was never designed to work in a changing climate. Climate change is not just about rising temperatures, but a whole host of factors including precipitation, wind speed, solar and infrared radiation, and humidity.
The new model developed at Princeton takes all these factors into account to assess drought. Due to its greater complexity, the model is more difficult to use, mostly because it demands much more data than just temperature. The required data has only recently become available thanks to advanced and more widespread satellite coverage.
Their model has already led to some reassessment by the IPCC, which stated that they found large uncertainties in drought trends. The Princeton/Canberra researchers admit that their findings do not mean that there will be fewer droughts in the future. Only that the link between drought and climate change is not quite as certain as previously believed.
This study has been published in the journal Nature
Drought-damaged crop image via Shutterstock