Fig. 1: Geographical distribution of R_S data and temporal changes of R_S in different time periods.

a A total of 2,428 observations in 693 published studies were retrieved from the SRDB, covering six types of biomes as denoted by different colors. The distribution of biomes displays clear latitude-dependent features. b The temporal trend of R_S changes in each decade based on the moving subset window analysis. The bars indicate the rates of R_S changes per decade, calculated as average annual R_S change (ΔR_S). The number above each bar refers to the number of R_S records belonging to the subset window. The color scale of the bars corresponds to the colors representing different periods in (c, d).***P < 0.001, **P < 0.010, *P < 0.050. c The relationship between R_S and year in 1987–1999. d The relationship between R_S and year in 2000–2016. The slope of linear regression indicates the rate of R_S changes in different time periods. The dot density represents data density at each point. Solid lines indicate significant trends (P < 0.050), while dashed lines indicate insignificant trends (P ≥ 0.050).