• KAVIRAJAN RAJENDRAN

      Articles written in Journal of Earth System Science

    • Future changes in rice yield over Kerala using climate change scenario from high resolution global climate model projection

      STELLA JES VARGHESE SAJANI SURENDRAN AJITHKUMAR B KAVIRAJAN RAJENDRAN AKIO KITOH

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      The impact of climate change on agricultural yield is one amongst the major concerns the world is witnessing. Our study focusses on rice yield prediction for an agricultural research station in Kerala with the help of climate change scenario input from the Meteorological Research Institute (MRI) Global Climate Model (GCM) projection under Representative Concentration Pathway 8.5 (RCP8.5). We have used Cropping System Model (CSM) Crop Estimation through Resource and Environment Synthesis (CERES) Rice within Decision Support System for Agrotechnology Transfer (DSSAT) package for predicting the yield. Our study has the novelty of using very high-resolution climate data from a model which is highly skilful in capturing the present-day climate features and climatic trends over India (in particular, over the Western Ghats), as input for simulating the future crop yield. From this study, we find that the rice yield decreases due to rise in temperature and reduction in rainfall, thereby reducing the crops maturity time in the future. Based on our results, the adaptation measures suggested to achieve better yield under future warming conditions are: (i) to opt for alternative rice varieties which have tolerance to high temperatures and consume less water, and (ii) shifting of planting date to the most appropriate window.

      $\bf{Highlights}$

      $\bullet$Impact study of future climate change on rice yield is carried out using CERES Rice Cropping System Model after systematic validation.

      $\bullet$Highly reliable climate change information from the projection by a 20-km resolution global climate model of MRI which is remarkably skilful in simulating the present-day Indian climate, is used as input for the crop model.

      $\bullet$Rice yield is found to decrease in future due to rise in temperature and reduction in rainfall, thereby reducing the crops maturity time.

      $\bullet$Adaptive measures of opting for temperature tolerant, high yielding rice varieties which consume less water and shifting of planting date to an appropriate window, are suggested to achieve better yield.

    • On the build-up of dust aerosols and possible indirect effect during Indian summer monsoon break spells using recent satellite observations of aerosols and cloud properties

      V B ARYA SAJANI SURENDRAN KAVIRAJAN RAJENDRAN

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      Association of higher (lower) rainfall with lower (higher) Aerosol Optical Depth (AOD) is consistent with the understanding that increased washout (build-up) and shorter (longer) life-time of aerosols occur in wetter (drier) conditions. Given the life-time of aerosols, it is imperative to examine how aerosols impact active/break (wetter/drier than normal) spells, prominent intraseasonal variability (ISV) of Indian summer monsoon (ISM), through their composite analysis using recent satellite observations of aerosols and cloud properties, circulation and rainfall. Dust aerosols can act as CCN and participate efficiently in cloud processes during active phase. During breaks, build-up of desert dust transported by prevalent circulation, is associated with lower cloud effective radius implying aerosols’ indirect effect where they can inhibit cloud growth in the presence of reduced moisture and decrease precipitation efficiency/rainfall. Correspondingly, correlation albeit small, between intraseasonal anomalies of AOD and rainfall is negative, when AOD leads rainfall by 3–5 days implying that indirect aerosols impact is effective during breaks, though it is not the dominant responsible factor. During breaks, lower shortwave flux at top of atmosphere hints at dust-induced semi-direct effect. As breaks are permanent features of ISM, incorporation of dust-induced feedbacks in models, is essential for improved ISV simulation and ISM prediction.

      $\bf{Highlights}$

      $\bullet$ Active (break) spell of summer monsoon is found to be associated with lower (higher) aerosol optical depth over India.

      $\bullet$ The build-up of desert dust transported to India by prevalent circulation during summer monsoon breaks, is associated with lower cloud effective radius which indicates the indirect effect of aerosols.

      $\bullet$ Predominant indirect effect induced by dust aerosols along with secondary semi-direct effect can lead to further rainfall reduction during intense and persistent breaks.

      $\bullet$ Proper incorporation of dust aerosol induced heating during breaks in models, is essential for simulation of intraseasonal variation inherent to Indian summer monsoon and thereby improving its prediction.

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