Abstract: Yunnan Province in Southwest China is vulnerable to droughts due to its distinctive
topography and local climate. Spring drought in Yunnan (SDY), which accounts for 70% of all
drought events, causes the most severe devastation. By examining the variation characteristics of
droughts in Yunnan from 1961 to 2020 in terms of the standardized precipitation evapotranspiration
index (SPEI), this present study shows that droughts in Yunnan have worsened in the past 60 years
on different timescales. Especially, the SDY exhibits notable interannual and interdecadal variations,
with no significant long-term trend, although the spring average regional temperatures have risen
at a rate of 0.33 ◦C/10a since 1961. Here, in order to quantify the contribution of the precipitation
and temperature, the two main meteorological impact factors, to the SDY under the exacerbation
of climate warming, the statistical analyses reveal that precipitation plays a more crucial role than
temperature in interannual and interdecadal SDY variations. Further, a diagnostic analysis of the
moisture budget equation indicates that suppressed vertical moisture advection is the most important
physical process affecting the reduced rainfall amount in spring, followed by the restricted horizontal
water vapor transport. Meanwhile, the weak Bay of Bengal (BOB) summer monsoon, which is likely
regulated by El Niño-like sea surface temperature anomalies (SSTAs) in spring, is closely linked with
the SDY. This mechanism provides the possibility of SDY predictability on a seasonal scale.

moisture budget; global warming; Bay of Bengal summer monsoon; ENSO