Indonesian forest fire in 1997 was caused by

The 1997 Indonesian forest fires were primarily triggered by severe drought tied to a strong El Niño event, which created unusually dry conditions that allowed fires—often set for land clearing—to spread uncontrollably. Satellite and scientific analyses identify the 1997–98 El Niño as the immediate climatic driver of drought across Indonesia, exacerbating peatland and forest susceptibility to burning [2]. Authoritative sources also note that land‑use changes (drainage, logging, plantation development) made forests vulnerable and enabled widespread conflagrations during the El Niño drought [3]. Thus the principal cause was the El Niño‑induced drought interacting with anthropogenic land‑use practices, not the greenhouse effect or ozone depletion.

Sources

1. [1] https://en.wikipedia.org/wiki/1997_Indonesian_forest_fires
2. [2] https://scholarspace.manoa.hawaii.edu/bitstreams/0890d80a-cfc5-4eb2-8401-45b59e03bf68/download
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 29: El Nino, La Nina & El Nino Modoki > Effects of El Nino & ENSO > p. 414