『Abstract
　Soil moisture is a key variable of the climate system. It constrains plant transpiration and photosynthesis in several regions of the world, with consequence impacts on the water, energy and biogeochemical cycles. Moreover it is a storage component for precipitation and radiation anomalies, inducing persistence in the climate system. Finally, it is involved in a number of feedbacks at the local, regional and global scales, and plays a major role in climate-change projections. In this review, we provide a synthesis of past research on the role of soil moisture for the climate system, based both on modelling and observational studies. We focus on soil moisture-temperature and soil moisture-precipitation feedbacks, and their possible modifications with climate change. We also highlight further impacts of soil moisture on climate, and the state of research regarding the validation of the relevance processes.
　There are promises for major advances in this research field in coming years thanks to the development of new validation datasets and multi-model initiatives. However, the availability of ground observations continues to be critical in limiting progress and should therefore strongly be fostered at the international level. Exchanges across disciplines will also be essential for bridging current knowledge gaps in this field. This is of key importance given the manifold impacts of soil moisture on climate, and their relevance for climate-change projections. A better understanding and quantification of the relevant processes would significantly help to reduce uncertainties in future-climate scenarios, in particular with regard to changes in climate variability and extreme events, as well as ecosystem and agricultural impacts.

Keywords: soil-water balance; land cover; climatic controls; boundary interactions; atmosphere; climate change』

Contents
1. Introduction
2. Soil moisture: Some definitions
3. The role of soil moisture in the land energy and water balances
4. Soil moisture-climate interactions and feedbacks: Soil moisture-evapotranspirtion coupling
　4.1. Classical conceptual framework
　4.2. Simulation of evapotranspiration in current climate models
　4.3. Regions of strong soil moisture-evapotranspiration coupling: Modelling synthesis
　4.4. Evidence from observations
5. Soil moisture-climate interactions and feedbacks: Impacts on temperature and precipitation
　5.1. Soil moisture-temperature coupling
　　5.1.1. Processes leading to soil moisture-temperature coupling
　　5.1.2. Regions of strong soil moisture-temperature coupling
　　5.1.3. Evidence from observations
　5.2. Soil moisture-precipitation coupling
　　5.2.1. Historical overview
　　5.2.2. Processes leading to soil moisture-precipitation coupling and soil moisture-precipitation feedback
　　5.2.3. Regions of strong soil moisture-precipitation coupling
　　5.2.4. Evidence from observations
6. Soil moisture-climate interactions and feedbacks: Further relevant aspects
　6.1. Climate persistence associated with soil moisture
　6.2. large-scale and non-local impacts of soil moisture anomalies
　6.3. Soil moisture-albedo interactions
　6.4. Soil moisture interactions with biogeochemical cycles
　6.5. Role of land cover and vegetation dynamics for soil moisture-climate interactions
7. Soil moisture-climate interactions in the context of climate change
　7.1. Projected changes in soil moisture and land climate
　7.2. Role of soil moisture changes for changes in summer climate variability
　7.3. Future hot spots of soil moisture-atmosphere coupling
　7.4. Are soil moisture-climate interactions amplifying or damping climate variability and anthropogenic climate change?
8. Validation datasets for soil moisture
　8.1. Ground measurements
　　8.1.1. Gravimetric measurements
　　8.1.2. Indirect in-situ measurement methods
　8.2. Remote sensing measurements
　　8.2.1. Microwave remote sensing
　　8.2.2. Gravity Recovery and Climate Experiment (GRACE)
　8.3. Atmospheric-terrestrial water-balance estimates and BSWB dataset
　8.4. LSM-based estimates
　8.5. Drought indices
　8.6. Methods to measure and estimate evapotranspiration
　8.7. Scale issues of observational datasets
9. Current research perspectives
　9.1. Model development and uncertainties
　9.2. New observational datasets and validation approaches
　9.3. Research applications: Subseasonal and seasonal forecasting, numerical weather prediction
10. Summary and conclusions
Acknowledgements
Appendix A. Coupling, feedbacks, interactions: Terminology
Appendix B. Coupling diagnostics
　B.1. Coupling diagnostics based on numerical experiments
　B.2. Correlation measures and empirical relationships
　B.3. Derivation of evapotranspiration sensitivity to soil moisture from its decay time
Acronyms and symbols
References