SPATIO-TEMPORAL MODELING OF SEMI-HETEROSKEDASTIC RAINFALL DATA USING A GSTAR-GARCH FRAMEWORK - Nurhayati, Nurhayati; Hamidi, Muhammad Rozzaq; Mukhaiyar, Utriweni; Sari, Kurnia Novita (BAREKENG: Jurnal Ilmu Matematika dan Terapan, 2026)