Potential of long-term satellite observations and reanalysis products for characterising soil drying: trends and drought events
Hirschi et al. (2025)
How do long-term drying trends influence the way we detect and interpret drought?
Under non-stationary conditions, where background soil moisture levels change over time, it becomes harder to tell whether soil moisture anomalies reflect short-term drought events or longer-term shifts in water availability.
Hirschi et al. (2025) examine this challenge by comparing long-term satellite soil moisture observations and land reanalysis products over the period 2000–2022. The study uses ESA Climate Change Initiative (CCI) soil moisture products, ERA5, ERA5-Land, and MERRA-2 reanalyses. To interpret product differences, the authors compare reanalysis precipitation and temperature trends with ground-based observations.
Their findings show that:
- The apparent severity and duration of drought events can differ depending on how long-term soil moisture trends appear in a dataset, even when the same drought definition is applied.
- Satellite-based and reanalysis products often show different long-term drying or wetting behavior, and these differences carry through to how drought events are detected and compared.
- Droughts tend to look shorter and sharper at the surface, while deeper soil layers show longer-lasting dry conditions that can extend beyond the surface signal.