Global Soil Moisture Estimation based on GPM IMERG Data using a Site Specific Adjusted Antecedent Precipitation Index

ABSTRACT

This study presents a global, hourly surface soil moisture estimation procedure based on precipitation and temperature data. Information on soil composition further helps to define the local characteristics of soil moisture development. An advanced antecedent precipitation index (API) is utilized to generate a global soil moisture product of high temporal resolution with the Global Precipitation Measurement (GPM) Missions Integrated Multi-Satellite Retrievals for GPM (IMERG) as main driver. The resulting global GPM API data set is compared against in situ measurements from the International Soil Moisture Network (ISMN) and is also evaluated against the soil moisture data set from the European Space Agency’s Climate Change Initiative (ESA CCI SM). The study shows that with empirically derived dampening factors the GPM API achieves a mean ubRMSD across the utilized in situ stations in different climates and vegetation zones of 4.68 $Vol\mathrm{\%}$ and a bias of 0.88 $Vol\mathrm{\%}$. The data set clearly represents the local soil moisture schemes with seasonal variations. When comparing with ESA CCI SM, the GPM API does perform better at the measurement sites concerning bias, correlation and error values. The data set is in most parts negatively biased compared to the ESA CCI SM, however better matches the mean soil moisture at ISMN stations. Overall, the GPM API delivers a very promising global, hourly surface soil moisture product at 0.1${ }^{\circ }$$\times$0.1${ }^{\circ }$ spatial resolution.

KEYWORDS:

• GPM
• IMERG
• soil moisture
• global
• precipitation
• ESA
• CCI
• SoilGrids
• ERA5
• ISMN

Acknowledgements

The authors thank the responsible institutions for providing the utilized data sets: NASA (GPM), ECMWF (ERA5), International Soil Reference and Information Centre (SoilGrids), TU Wien (ISMN), ESA (ESA CCI SM).

Disclosure statement

No potential conflict of interest was reported by the authors.