|Title||Evaluation of daily soil moisture deficit used in Australian forest fire danger rating system|
|Year of Publication||2017|
|Authors||Kumar, V, Dharssi, I|
|Institution||Bushfire and Natural Hazards CRC|
The fuel availability estimates in McArthur Forest Fire Danger Index used in Australia for issuing operational fire warnings are partly based on soil moisture deficit, calculated as either the Keetch–Byram Drought Index (KBDI) or Mount’s Soil Dryness Index (SDI). These indices are essentially simple water balance models designed to estimate soil moisture depletion in the upper soil levels. In the present study, daily values of the above two indices are calculated over Australia at 0.05 resolution from 1974 onwards. A detailed verification of these two models against in-situ soil moisture measurements from CosmOz, OzNet and OzFlux networks are performed. The validations are done using soil moisture observations that represent both surface and deeper soil moisture. The verifications for deeper soil are restricted to OzNet and OzFlux, as only these two networks provide corresponding to observations. The verification results show that both KBDI and SDI have relatively low skill in estimating shallow layer (0 – approx. 30 cm) soil moisture compared to a much deeper soil profile (0 – approx. 1m). The modest sensitivity of both KBDI and SDI to weather changes indicate that they are not an accurate measure for estimating duff layer soil moisture.