Reconstruction of gridded Standardized Precipitation Evapotranspiration Index (SPEI) across China during the last millennium via assimilating an expanded proxy network

(1) Data Content: This dataset comprises spatiotemporally-complete reconstruction of the growing-season (June, July, August) Standardized Precipitation Evapotranspiration Index (SPEI-03) across China during the last millennium (1000-2000 CE). The reconstructed SPEI fields have a spatial resolution of approximately 250 km (≈1.875° lat-lon grid). SPEI-03 reflects water availability during crop growth stages and is a core indicator of agricultural drought. The dataset includes: 1) 50 reconstructions derived from 50 Monte Carlo realizations, and 2) the corresponding mean and ±1 standard deviation (Sigma) calculated from the ensemble of 50 realizations. Qualitative validation, cross-validation and independent verification demonstrated that, compared to SPEI derived solely from climate model simulations and previous reconstructions, this dataset exhibits higher reliability over China. (2) Data Production Method: We reconstructed this dataset using a paleoclimate data assimilation framework. The system assimilated 420 proxy records - far more than previous SPEI reconstructions for China - including 76 dry/wet grade series from Chinese historical documents. These documentary records, not used in earlier studies, help address the spatial data gap over eastern China in previous reconstructions. A time-averaged Ensemble Square Root Filter (EnSRF) algorithm was applied for assimilation. The static prior ensemble (ensemble size N = 100) was randomly sampled from the “Global SPEI over the Common Era” dataset (see dataset details at 10.5281/zenodo.18411292), which is based on monthly climate variables from MPI-ESM model simulations in CMIP6 past2k experiment. Please contact the producer Miao Fang (E-mail: [e-mail]) for more information about the details of the reconstructions.