Overview

The important role of soil moisture for the environment and climate system is well known. Soil moisture influences hydrological and agricultural processes, runoff generation, drought development and many other processes. It also impacts on the climate system through atmospheric feedbacks. Soil moisture is a source of water for evapotranspiration over the continents, and is involved in both the water and the energy cycles. Soil moisture was recognised as an Essential Climate Variable (ECV) in 2010. 

Soil moisture anomalies for the year 2021 derived from the ESA CCI COMBINED v07.1 product.

The Soil Moisture CCI project is part of the ESA Programme on Global Monitoring of Essential Climate Variables (ECV), better known as the Climate Change Initiative (CCI), initiated in 2010 and producing an updated soil moisture product every year. The ESA CCI Soil moisture product has contributed to hundreds of hydrological and climatological studies worldwide, as well as the annual BAMS' "State of the Climate" reports. 

CCI Soil Moisture produces:

• Annually algorithmically updated global climate data record of soil moisture spanning over 40 years.
• 3 separate soil moisture products derived from active, passive and combined (active + passive) sensors and a break-adjusted product based on combined.
• 13 public releases to date, each updated with new sensors and extended time series.

The dataset ingests soil moisture datasets derived from the sensors listed in the figures below. In particular, the following datasets are used (at ESA CCI SM v07.1):

• ASCAT-A, -B and -C data are generated through the HSAF soil moisture project which can be accessed on the EUMETSAT HSAF soil moisture website. At v07.1, data records H119 is ingested.
• ERS data is processed by the Microwave Remote Sensing Group at TU Wien.
• All passive datasets are processed using the LPRMv7.1 algorithms (except for the L-band SMOS and SMAP datasets, processed with LPRMv6.2), designed and implemented by Vandersat.

ESA CCI soil moisture v07.1 product utilizes 5 active and 12 passive microwave sensors.

Merging scheme of the ESA CCI SM v7.1 algorithm. For more information on the product generation please refer to the product documentation.

CCI+ Scientific Study (ongoing)

While the surface soil moisture products delivered by ESA CCI have proven valuable contributions to many climate applications, particularly carbon and vegetation modellers have expressed a strong interest in long-term satellite-based rootzone soil moisture products for linking vegetation phenology and biomass carbon allocation to moisture availability in the soil (Dorigo et al. 2017).

The goal of this study is to develop such a product based on land surface models and data assimilation. More specifically, a global rootzone soil moisture dataset will be established for the years 2002 to 2019 with daily temporal- and 0.25° spatial resolution.

The modelling will be done using two fundamentally different land surface models (Noah-MP and ISBA). Additionally, three different datasets will be assimilated in different combinations containing information of surface soil moisture, leaf area index, and vegetation optical depth. The resulting datasets will be evaluated using in situ data from the international soil moisture network and existing rootzone soil moisture datasets using QA4SM.

These efforts are made to investigate the requirements and R&D activities needed for the development of a root zone soil moisture product.