Tropical Pacific Ocean SST teleconnections for the vegetation photosynthetic activity in India
Authors: Varghese Roma , K. Behera Swadhin , Behera Mukunda Dev 
Published: February 2023

Sea surface temperature (SST) is a key physical attribute of upper ocean thermal conditions that provide crucial information on the earth&#8217;s climate system by playing vital role in air-sea interactions. Some regional-scale SST variations are linked to large-scale climate variability which has catastrophic consequences in the social-economic sectors of many countries. Such anomalous SST conditions in the tropical oceans causes severe impacts on the functioning of terrestrial ecosystems by altering the fluxes of heat and moisture on land, and thus threatens terrestrial carbon dynamics as well as global food security. Thus, monitoring the vegetation response to SST anomalies is fundamental to understand, quantify, and predict the effects of oceanic variability on terrestrial vegetation activity. Solar-induced chlorophyll fluorescence (SIF) is a promising plant biophysical variable that has been used for the continuous observation of global vegetation activity, especially the photosynthetic characteristics. Our study comprehensively evaluates the relationship between tropical Pacific SST variability and SIF anomalies across India to assess the spatial and temporal variability in the ocean-vegetation interactions. Overall, SIF anomaly over the Indian mainland shows negative association with SST variability in the eastern equatorial Pacific. The persistence of warm anomalies in this oceanic region forces the reduction of average SIF in all the Indian agro-climatic zones notably during the summer monsoon. While during the years of cold anomalies in the eastern equatorial Pacific, SIF appears to be enhanced. Similarly, the composite of SIF demonstrated negative (positive) anomalies during the years of positive (negative) SST anomalies. However, the implications of SST variability on the SIF anomalies are not uniform all over India even during the summer monsoon. There exist a high spatial and temporal variability in the observed SST-SIF interactions. Within the monsoon months, the influence of both positive and negative SST anomalies was predominant only during July and August across much of the Indian mainland. In addition, this oceanic influence was also significantly notable in March, particularly in the Deccan plateau. Overall, the impact of warm anomalies is comparatively stronger on the functioning of the terrestrial ecosystem in India than the cold anomalies with a limited influence mainly over the southern peninsular region. This difference in the implications of positive and negative SST anomalies is evident in all the months except during March, July, and August. Annually, SST variability in the eastern equatorial Pacific significantly contributes to the interannual variability of SIF anomalies in Gujarat plains and hills, Western plateau and hills, Southern plateau and hills, Central plateau and hills, Eastern plateau and hills, and Western dry region. The observed significant SST-SIF linkage between the eastern equatorial Pacific and the Indian vegetation was feasible through the atmospheric teleconnections. The present study provides the fundamental information that aids the early detection of possible vegetation growth anomalies to various climate extremes associated with the tropical Pacific region. This can be useful for planning long-term strategies and policies to improve precision agriculture and forest management practices in India.&#160;