A severe agricultural drought swept Central Asia in 2021, causing mass die-offs of crops and livestock. The anthropogenic contribution to declines in soil moisture in this region over recent decades has remained unclear. Here we show from analysis of large ensemble simulations that the aggravation of agricultural droughts over southern Central Asia since 1992 can be attributed to both anthropogenic forcing and internal variability associated with the Interdecadal Pacific Oscillation (IPO). Although the negative-to-positive phase transition of IPO before 1992 offset human-induced soil moisture decline, we find that the positive-to-negative phase transition thereafter has doubled the externally forced rate of drying in the early growing season. Human-induced soil moisture loss will probably be further aggravated in the following century due to warming, albeit with increasing precipitation, and our simulations project that this trend will not be counterbalanced by the IPO phase change. Instead, this internal variability could modulate drying rates in the near term with an amplitude of −2 (+2) standard deviation of the IPO trend projected to amplify (weaken) the externally forced decrease in surface soil moisture by nearly 75% (60%). 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.

2021年一场严重的农业干旱席卷中亚，造成农作物和牲畜大量死亡。近几十年来，人为对该地区土壤水分下降的贡献仍不清楚。在这里，我们通过对大型集合模拟的分析表明，自 1992 年以来中亚南部农业干旱的加剧可归因于人为强迫和与年代际太平洋涛动 (IPO) 相关的内部变率。尽管 1992 年之前 IPO 的负向正相变抵消了人为引起的土壤水分下降，但我们发现此后的正向负相变使生长季节早期的外部强迫干燥率翻了一番。尽管降水量增加，但由于变暖，下个世纪人为引起的土壤水分流失可能会进一步加剧，我们的模拟预测这一趋势不会被 IPO 相变所抵消。相反，这种内部变化可能会在短期内调节干燥率，幅度为 IPO 趋势的 −2 (+2) 标准偏差，预计会放大（减弱）表面土壤水分的外部强制减少近 75%（60%） ). 研究结果强调，这个气候敏感地区的决策者需要考虑人为强迫与 IPO 的自然变率之间的相互作用。这种内部可变性可以在短期内调节干燥率，幅度为 IPO 趋势的 −2 (+2) 标准偏差，预计会放大（减弱）表面土壤水分的外部强制减少近 75% (60%)。研究结果强调，这个气候敏感地区的决策者需要考虑人为强迫与 IPO 的自然变率之间的相互作用。这种内部可变性可以在短期内调节干燥率，幅度为 IPO 趋势的 −2 (+2) 标准偏差，预计会放大（减弱）表面土壤水分的外部强制减少近 75% (60%)。研究结果强调，这个气候敏感地区的决策者需要考虑人为强迫与 IPO 的自然变率之间的相互作用。