Fig. 2: Spatiotemporal distribution of the statistically significant correlations between vegetation growth and water availability indices over the last three decades.
From: Observed increasing water constraint on vegetation growth over the last three decades
a, b Show distribution of correlation coefficients (RNDVI-SPEI03 and RNDVI-scPDSI) between normalized difference vegetation index (NDVI) anomaly and 3-month Standardized Precipitation-Evapotranspiration Index (SPEI03) and Palmer Drought Severity Index (scPDSI). The horizontal axis of the color legend is the correlation coefficient between NDVI anomaly and SPEI03 (scPDSI) for the entire study period, the vertical axis of the color legend is the trend of correlation coefficient for the 30 five-year moving windows, no color indicates unvegetated regions. The chartreuse color stands for vegetation water surplus regions where water surplus has been decreasing; navy color indicates vegetation water surplus regions that have been experiencing an increase in water surplus; magenta color is used for water deficit regions that have been seeing an increase in water deficit; and regions colored in yellow are characterized by water deficit and a decrease in water deficit. c, d Show the temporal trends of significant changes in percentage areas associated with water deficit and water surplus responses using 5-year moving windows. Blue color stands for the water surplus response and red color for water deficit response. All the trends of water deficit and water surplus responses are significant in linear trend test and Mann–Kendall trend test (p < 0.05). X-axes of (c, d) are binned using 5-year moving window to smooth out time series fluctuations and highlight the trends.
