ABSTRACT Aim Quantitative tools for reconstructing past hydroclimate in Southeast Asia remain limited. We therefore develop modern calibrations linking non‐arboreal pollen (NAP; excluding forest‐understory herbs and fern spores) to Normalised Difference Vegetation Index (NDVI) and mean annual precipitation and evaluate their out‐of‐sample performance when applied to marine pollen records from the southern South China Sea (SCS). Location Central and eastern Thailand; western Peninsular Malaysia; southern SCS (exposed Sunda Shelf during glacial lowstands). Time Period Modern pollen calibration: application to the last glacial maximum (LGM). Major Taxa NAP from tropical ecosystems. Methods We compiled 88 topsoil pollen samples (33 new from Thailand, plus 55 published from Malaysia). Interpolated mean annual precipitation (WorldClim v2.1 climatology) and NDVI were extracted for each site. Linear regressions quantified NAP–NDVI relationships within Thailand and across Thailand–Malaysia. A Huber regression model predicting precipitation from pollen predictors (NAP and high‐mountain pollen) was evaluated using 5‐fold cross‐validation. Segmented (piecewise) regressions identified pollen‐space thresholds separating vegetation states. These calibrations and associated thresholds were applied to published marine pollen records from the southern SCS. Results and Main Conclusions NAP covaries strongly and linearly with the NDVI across Thailand–Malaysia. A Huber regression linking NAP to mean annual precipitation shows robust out‐of‐sample predictive skill under 5‐fold cross‐validation ( R 2 = 0.77; RMSE = 365 mm year −1 ). Segmented regression further identifies a practical pollen‐space threshold of ~51% NAP that discriminates open landscapes (wooded grasslands) from closed forest in eastern Thailand. Applied to ten published marine pollen records from the southern SCS (shelf and slope; ~25–18 cal ka BP, LGM), our NDVI‐ and precipitation‐based reconstructions, together with the threshold framework, suggest that closed forest prevailed in the western and eastern sectors, whereas slightly more open forest characterised the southern sector during the LGM period. Overall, inferred humidity conditions appear broadly comparable to those of modern surrounding coastal regions.
Gong et al. (Sun,) studied this question.