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Role of Soil Moisture Coupling on Surface Temperature Variability Over Indian Subcontinent

Soil moisture is a key climate variable impacting local to global scales. This study investigates soil moisture-temperature feedbacks during Indian summer monsoon, focusing on recent decades' break monsoon events. Analysis of observational data and modeling highlights the importance of soil moisture in influencing temperature variability under different climate regimes.

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Role of Soil Moisture Coupling on Surface Temperature Variability Over Indian Subcontinent

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  1. Role of Soil Moisture Coupling on the Surface Temperature Variability Over the Indian Subcontinent J. Sanjay M.V.S Rama Rao and R. Krishnan Centre for Climate Change Research (CCCR) Indian Institute of Tropical Meteorology (IITM), Pune (An Autonomous Institute of the Ministry of Earth Sciences, Govt. of India) Email: sanjay@tropmet.res.in

  2. Soil moisture is a key variable of the climate system • It is involved in a number of feedbacks at the local, regional and global scales, and plays a major role in climate-change projections (Seneviratne et al. 2010) • In this study we focus on soil moisture-temperature feedbacks, and their possible modifications with climate change

  3. The Indian summer monsoon rainy season (June-September) is characterized by variations on a wide range of timescales across diurnal, synoptic, intraseasonal, interannual and decadal scales • Surface temperatures over north-central India can increase rapidly to above-normal values during break monsoon periods (e.g., Raghavan 1973) • During recent decades, a significant increase in the incidence of prolonged monsoon-breaks has been observed during the core monsoon rainy months of July and August over India (Ramesh Kumar et al. 2009)

  4. Changing characteristics of break monsoon spells during the recent three decades • Active and break events are defined as periods during the peak Indian monsoon months of July and August, in which the normalized anomaly of the rainfall over the monsoon core zone exceeds +1.0 or is less than −1.0 respectively, provided the criterion is satisfied for at least three consecutive days (Rajeevan et al. 2010) • This methodology was applied to two observed daily precipitation datasets • APHRODITE(Asian Precipitation—Highly-Resolved Observational Data Integration Towards Evaluation of Water Resources ; Yatagai et al. 2012; 0.5o x 0.5o) • IMD (India Meteorological Department; Rajeevan et al. 2005 ; 1o x 1o) Frequeny of Break Days during the recent 3 decades Sanjay et al.

  5. Observed Active and Break Day Anomaly Composite for the recent three decades Sanjay et al. APHRODITE Rain Tair • Indicates to the role of local feedbacks such as land-atmosphere coupling in maintaining higher break monsoon temperatures over a wider region in recent decades

  6. Soil moisture–Air temperature Coupling during Monsoon Season • Derived using the global multimodel analysis (MMA) of land surface state variables and fluxes from the Global Soil Wetness Project-2 (GSWP-2; Dirmeyer et al. 2006; 1°X1° grid; 1986-1995) Sanjay et al. • The SM-temperature coupling is expected to be strongest in transitional zones between dry and wet climates where a strong dependency of ET on SM (ie., moisture limited) is superposed with large mean ET and its variability (Seneviratne et al., 2010).

  7. Processes contributing to soil moisture–temperature coupling and feedback loop Estimations of soil moisture–temperature coupling diagnosed with JJA ρ(E,T)

  8. Role of soil moisture changes for changes in summer climate variability under different climate regimes (CTL vs SCEN, i.e present vs future) • In this hypothetical scenario, the mean seasonal cycle of SM in the present-climate conditions is largely confined within a range where it does generally not limit ET (radiation-limited ET regime) • It shifts to a SM-limiting regime during the summer season under the future-climate conditions

  9. GSWP-2 MMA Wet and Soil Conditions Anomaly Composite Sanjay et al. Moist to Transitional SM regime Energy-limited to SM-limited EF regime • The dry composite shows strong SM-temperature coupling

  10. In Conclusion • The latest ensemble of climate models participating in the Coupled Model Intercomparison Project phase 5 (CMIP-5) consistently projects significant increases in day-to-day rainfall variability during Indian summer monsoon season under unmitigated climate change (Menon et al. 2013) • Hence this observation-based analysis, by taking into account the respective period of the summer monsoon season where SM is most likely to be limiting over some parts of India, suggests that the sub-seasonal SM-temperature coupling is going to play a dominant role while assessing the regional climate change impacts on livelihood • Proper representation of these aspects of land-atmosphere interactions in CORDEX RCMs will enhance the confidence in providing regional climate projections with them

  11. Many Thanks to: • CORDEX Workshop Organisers • ICIMOD, Kathmandu, Nepal Thanks for your attention Email: sanjay@tropmet.res.in

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