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Investigating soil moisture-climate interactions in a changing climate: A review

Investigating soil moisture-climate interactions in a changing climate: A review. Sonia I. Seneviratne ⁎, Thierry Corti, Edouard L. Davin, Martin Hirschi, Eric B. Jaeger, Irene Lehner, Boris Orlowsky, Adriaan J. Teuling Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland.

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Investigating soil moisture-climate interactions in a changing climate: A review

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  1. Investigating soil moisture-climate interactions in a changing climate: A review Sonia I. Seneviratne ⁎, Thierry Corti, Edouard L. Davin, Martin Hirschi, Eric B. Jaeger, Irene Lehner, Boris Orlowsky, Adriaan J. Teuling Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland

  2. Many complex land processes and feedbacks!

  3. Some Preliminaries • “Evapotranspiration” = net effect of ground evaporation and plant transpiration (mostly the latter) • More than half of solar radiation used for land evapotranspiration • Soil Moisture controls the partitioning of sensible and latent fluxes (Bowen Ratio) with implication on meteorology.

  4. Clouds due to Plant Transpiration • Dry Season in the Amazon Basin • Plants more active in Dry Season!

  5. Role of Soil Moisture is 2-fold: Coupled through evapotranspiration term dS/dt = P – E – Rs – Rg dH/dt = Rn – λE – SH– G

  6. Soil-Moisture affects climate through Δ Evapotranspiration (Latent heat flux) Classic Conceptual Framework : 2 regimes Strong coupling EF independent of soil moisture (e.g. Amazon in Summer) No evaporation (e.g. Sahara)

  7. SM only affects climate in these transitional “hot spots” regions 1. strong SM-EVAP coupling2. large mean EVAP DRY : EVAP controlled By Soil moisture, but mean too small WET: large EVAP, but not controlled by SM *AGCM ensemble simulations from GLACE

  8. OBS evidence for different SM regimes “SM limited” “ Transitional ” “Energy Limited” Artic tundra Temperate Forest Dry Mediterranean *Different Drivers of SM conspire to make similar EVAP in summer, despite different climates / land cover

  9. Soil Moisture – Temperature Coupling Potential Positive feedback

  10. Regions of strong SM-TEMP coupling Transitional “hot spots” zones Where temperature Depends on Soil-moisture Radiation limited regimes SM limited regimes

  11. Soil Moisture – Precip Coupling ?? Don’t even know the Correct sign here!

  12. Regions of strong SM-Precip coupling • In GLACE models, EVAP sensitivity appears to control both T and P coupling • BUT significant inter-model variability • GLACE models may not be able to simulate negative SM-Precip feedbacks found in CRM, RCM, and OBS

  13. Other SM–climate interactions • Persistence (“memory”) of soil moisture anomalies • SM acts as both water and energy storage • Potential implications for subseasonal/seasonal forecasting • Again depends on “hot spot” regions where coupling is strong • Non-local and Large scale impacts • e.g. Advection of dry/hot air over negative SM anomalies • Apparently relevant for spread of European heat waves • Soil Moisture – Albedo interaction • Soil moisture anomalies affect both bare-soil and vegetative albedo • Interaction with Biogeochemical cycles • CO2 uptake by plants coupled with water loss via transpiration • Less water  Less productive plants  More CO2

  14. Δ Soil Moisture in a warming world Projected Decrease In precipitation in mid-Lat and sub-arid Regions Drives SM decrease * Note no change in SM in wet places in spite of increased Precip (“energy-limited” regime)

  15. - Again Mediterranean Hot Spot Clear • Changes in • Climate Variability • Cannot be simply • Derived from changes • In mean climate

  16. How SM can affect Climate Variability Seasonal cycle “Radiation-Limited” Wet regime “SM-limited” Transitional regime If a region shifts to a SM-limited regime and becomes a coupling “hot spot”  then EVAP variability depends highly on SM and  then SM is an important driver of TEMP (via Bowen Ratio)

  17. Projected changes in SM-Temp coupling Red = Soil moisture limited regime Blue = Radiation limited regime * Projected decrease in Precip causes Central Europe to switch from Blue to Red

  18. Does SM-climate interactions amplify or damp Climate Variability? • Wet soil moisture regime • EVAP is insensitive to soil moisture and has no effect on CLIVAR • Transitional soil moisture regime - EVAP very sensitive to soil moisture and significantly impacts climate • Dry soil moisture regime • EVAP very sensitive to soil moisture, but very limited If Climate changes from : Wet  Transitional = Increased Climate Variability Transitional  Dry = Decreased Climate Variability

  19. Challenges and uncertainties • Significant divergence among models regarding SM–Precipitation feedbacks • Still don’t know what sign is here, let alone magnitude! • Evap sensitivity to soil moisture highly variable among LSMs

  20. Challenges and uncertainties (cont.) • Better Diagnostics to validate models • Coupling of key processes often more important to climate prediction than absolute values of temp, evap, etc.. • How to assimilate disparate land data sets • More comprehensive ground network given land heterogeneity

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