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Present methods to predict droughts may be unreliable under climate change

Hydrologists and water resource managers have long depended on historical data for predicting droughts. However, according to a new study, this route may not give reliable predictions due to climate change caused by human activities. The study was carried out by researchers from the Indian Institute of Science, Bangalore.

Droughts have been part of human existence since thousands of years. A look at the past records of the droughts shows that they occur in more or less in fixed intervals. This observation, called the ‘stationarity’, has been the backbone of water resources planning so far. However, the study by Prof Pradeep Mujumdar and Arpita Mondal suggest that stationarity may not hold good any more, thanks to human induced climate change.

“Traditionally, the concept of stationarity is used for hydrologic designs (say, long term planning against droughts). That is, a water manager may plan for a drought that is expected once in 100 years. However, under climate change, stationarity may not be a valid assumption”, explained Arpita Mondal.

The researchers analysed data pertaining to Colorado river in the United States to predict how frequently the hydrologic droughts would return to the Colorado river. Using a mathematical model that takes into account the effects of climate change, they concluded that historical data may not give reliable clues to predicting the return levels of droughts. This is because, rising temperatures have already started influencing the precipitation and the evaporation, two prime drivers in the water cycle.

Depending on the severity, and the ability of a society to manage them properly, droughts can have varying consequences. Historically, they have forced humans to migrate to different areas, and sometimes resulted in large number of deaths of living beings, including humans. For example, in India alone, millions of people have died in the last three centuries because of droughts.

Over the years, a significant amount of basic research has gone into understand droughts better, which in turn, has helped us manage our water resources better. Now, we should understand how droughts are influenced by a changing climate. As Arpita says, her study of the Colorado river, provides an estimate of how droughts are likely to change in the future because of climate change.

The lessons learnt from the Colorado rivers are not directly applicable to Indian rivers because, they are influenced by different hydrologic processes, says Arpita. For example, the Colorado river, like other rivers in the Western United States, are fed by snow, whereas most of the Indian rivers are depend heavily on monsoon. However, such studies clearly show that the methods that worked till now may not be so successful in the backdrop of climate change. “Climate change is expected to significantly influence the water cycle and further aggravate the water stress already existing in the country. These research contributions are thus an attempt at a better understanding of these changes with a view to improve drought resilience”, says Arpita.

About the authors:

Prof Pradeep Mujumdar is with the Department of Civil Engineering, Indian Institute of Science, Bangalore and the Divecha Center for Climate Change, IISc. Arpita Mondal is his PhD student in Civil Engineering.

Contact:

Pradeep Mujumdar

E-mail address: pradeep@civil.iisc.ernet.in; Tel.: +91 80 2293 2669

The paper appeared in the journal Advances in Water Resources. http://dx.doi.org/10.1016/j.advwatres.2014.11.005