Geoscience Australia's Sentinel-2 maps flag dry vegetation in the normal-risk ACT

Geoscience Australia's public tool ^[3] measures moisture indirectly. Sentinel-2 records how vegetation reflects light, and that reflectance changes as plants gain or lose water ^[7]. The tool converts those changes into an estimate of fuel moisture content, the water in vegetation relative to its dry weight ^[4]. Below a critical level, vegetation ignites more easily, burns hotter and spreads faster, and that level differs between vegetation types ^[5]. A patch flagged as drier than usual is dry relative to its own history, and judging whether it has passed the critical level for its vegetation type needs separate information ^[5].

The tool's advantage over the regional outlook is scale. Each 20-metre pixel covers 400 square metres, so a single hectare holds 25 readings ^[3]. The national outlook, issued in August by the Australasian Fire and Emergency Service Authorities Council, weighs weather, climate and fuels to mark areas of above-normal spring risk ^[1]. It did not mark the ACT ^[8]. According to the authors of the account, published on phys.org, slightly more than half the territory was at least as moist as usual in August ^[9]. The remaining share, a little under half, was drier or much drier than average, particularly in parts of the south ^[9][1]. In August 2018 and 2019, before the Black Summer fires, roughly two-thirds of the ACT was dry or very dry ^[10]. The two comparisons use slightly different category names, so the gap between them is approximate ^[9][10].

The pace of drying is a second signal. Between July and August 2026, ACT vegetation dried faster than in most years of the past decade ^[12]. In 2018 and 2019, August was drier overall but the drop from July was smaller ^[13]. This year a larger share of the territory is classed as wet or moving from wet to dry, while parts of the south are already unusually dry for August ^[14]. If the rapid drying continues, the authors wrote, some of those transitional areas could move into the dry category later in spring ^[15]. They singled out parts of the southern ACT where vegetation is "drier than in the north, drier than in previous years and rapidly getting even drier" ^[16].

The dry patches have also moved. A planner relying on where it was dry before Black Summer would be looking partly in the wrong places this year ^[11]. Some of the locations now drier than usual were far wetter in 2018 and 2019 ^[11].

The thing the ACT example doesn't tell you is how accurate the maps are. The account does not compare the satellite estimates with field-measured fuel moisture, or check past dryness anomalies against where fires started. The baseline is also short. The archive begins in 2015 ^[6], so "usual" for any pixel rests on roughly 11 years of observations ^[2]. One territory in one month is a demonstration.

The first use the authors describe is prescribed burning. Land managers around Canberra burn in spring before the hotter months, and identifying suitable windows is hard ^[18]. Across Australia, they argue, the maps could help agencies, land managers, Indigenous communities and landholders decide where closer monitoring and preparation deserve attention ^[17]. The council behind the national outlook already tells every community to understand its local conditions, because fires can occur in regions rated normal and conditions vary within them ^[2].