Spatial-temporal variations in drought conditions and their climatic oscillations in Central Asia from 1990 to 2019

The rapid shrinking of the Aral Sea has prompted the scientific community to focus on Central Asian drought. To clarify the moisture conditions of Central Asia over the past 30 years and to investigate the climate drivers of change, in this study, we used the Palmer Drought Index (PDSI) to assess the spatial and temporal characteristics of drought in the five Central Asian countries (Kazakhstan, Uzbekistan, Turkmenistan, Tajikistan and Kyrgyzstan) from 1990 to 2019. PDSI was combined with the cross-wavelet transformation to reveal the driving influence of climate oscillations on drought conditions. The results showed that the drought indicators displayed a cyclical alternation with an increasing variability, a weakening of the dry summer/autumn and wet winter/spring seasonal drought characteristics, and the possibility of a new dry period after 2018. The general drought intensity gradually decreased from the southwest to the northeast and progressively increased from the southeast mountainous area to the central and western plains. The drought center shifted from the southwestern hinterland to the northwestern regions of Kazakhstan. The Pamir and West Tianshan Mountains showed a fluctuating and increasing drought trend. The Tibetan Plateau Index (TPI) showed an apparent driving effect on PDSI changes, with high cyclical intensity throughout the 1990-2019 period (1-3 years 1995-2000, 4-5 years 2010-2015, 8-10 years 2010-2015, and 8-10 years 2016-2019) with three distinct interannual-scale oscillatory cycles. Overall, drought conditions tended to improve, with increased drought variability and significant spatial variability; the TPI is the atmospheric oscillator driving PDSI variability.