Chinese researchers reveal causes of agricultural drought

Chinese researchers have found that anthropogenic external forcing and the natural internal variability of the climate system together have led to aggravated droughts across southern Central Asia in its early growing season over the past three decades.

The study was published recently in the journal Nature Geoscience.

"Agricultural drought refers to soil moisture deficits, which is closely related to meteorological factor changes and usually happens after meteorological drought," said Jiang Jie, first author of the study, a researcher at the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences.

"The anthropogenic external forcing mainly refers to the increase in greenhouse gas concentrations in this research," Jiang added. The continued emission of greenhouse gases has resulted in rapid warming across Central Asia, which has further led to increased evapotranspiration and reduced soil moisture in this region.

Jiang explained that the prominent natural variability that influences Central Asian droughts is a long-term oscillation of sea surface temperatures in the Pacific Ocean, or the Interdecadal Pacific Oscillation (IPO), which waxes and wanes every 20 to 30 years. The recent IPO cycle since the 1990s resulted in reduced spring rainfall across southern Central Asia and a subsequent decrease in soil moisture in the early growing season.

"Both the human-induced warming and the IPO-dominated reduction in spring rainfall led to soil moisture deficits over southern Central Asia, and finally the aggravated agricultural droughts in the past three decades," Jiang said.

The scientists also predicted that dominated by human-induced warming, the droughts in Central Asia will worsen in this century. Even if the IPO begins a warm phase that is favorable to more precipitation in the next few decades, it would still have difficulty countering worsening droughts.

"The IPO could not counterbalance the human-induced drying trend over Central Asia, but it could modulate the drying rate in the near-term," said Zhou Tianjun, corresponding author of the study and a researcher at IAP.

The findings highlight the need for the interplay between anthropogenic forcing and the natural variability of the IPO to be considered by policymakers in this climate-sensitive region, Zhou added.  ■