3.1 Inter-annual precipitation fluctuation
The precipitation amount in 2019 and 2020 was 323.1 and 205.2 mm, respectively (Fig. S1). The precipitation amount in growing season (from April to September) in 2019 and 2020 was 272.6 and 176.3 mm, respectively, and accounted for 84.4% of annual precipitation in 2019 and 85.91% of annual precipitation in 2020 (Fig. S1). The precipitation amount in growing season in 2019 was higher than that in long-term (246.6 mm; 1980–2020 average), but that in 2020 was lesser than the long-term average (Fig. S1). Precipitation in the early stage of growing season (from April to July) in 2019 was much higher than that in 2020 (Fig. S1). However, precipitation in August in 2020 was higher than that in 2019 (Fig. S1).