Build Up Index (BUI) is derived from which combination of indices?

• A. FFMC and DMC
• B. DMC and DC
• C. FFMC and DC
• D. ISI and FFMC

Answer: (B)

Build Up Index measures how much fuel is available to burn in the forest floor, especially the litter and duff layers. It is derived from the Drought Code and the Duff Moisture Code. The Drought Code reflects how dry the deeper litter and duff are, while the Duff Moisture Code records the moisture level of the duff layer itself. Together, these two codes describe the overall buildup and dryness of the fuels that can sustain a fire, so BUI is calculated from them. This is why high DMC and DC values push the Build Up Index higher, signaling greater potential fuel availability even if surface moisture is moderate. In contrast, FFMC governs surface fuel moisture and, along with wind, drives the Initial Spread Index, which then combines with BUI to form the Fire Weather Index. So the correct pairing is DMC and DC.