Fig. 3.

Variations in annual mean PLAM index (a), total radiation (J m⁻²) (b) and relative humidity (%) (c) in BTHs, YRD, SCB, and PRD during the 2015–2020 period. PLAM index was estimated by using the methods developed in previous studies (Zhang et al., 2009 and 2019 [7,36]; Wang et al., 2012 and 2013 [37,38]; total radiation and relative humidity data were obtained from China Meteorological Administration [39].