EXAMINING THE ROLE OF GROUNDWATER IN THE SPATIO-TEMPORAL VARIATION OF WATER USE EFFICIENCY OF TERRESTRIAL ECOSYSTEM IN INDIA

Abstract

Terrestrial ecosystem (TE), a vital component of the global carbon cycle, plays an important role in carbon sequestration. Water is one of the important factors for the growth of plants and hence the availability of water and its effective utilization is of major concern. Ecosystem Water Use Efficiency (WUEe), an important ecohydrological indicator, represents the relationship between carbon and water exchanges at ecosystem level, and it is defined as net carbon uptake (represented as Net Primary Productivity, NPP) per unit of water consumed (represented as Evapotranspiration, ET). Since, groundwater is one of the important sources of moisture for the terrestrial ecosystem, it can also influence the spatial as well as the temporal variation of WUEe. This interaction can vary with the variation in the type of climate zone, Land Use Land Cover (LULC) and irrigation. Thus, this paper aims to study the interaction between groundwater and productivity of terrestrial ecosystem at different spatial scales. The role of irrigation in the productivity of croplands was also studied to deepen our understanding of the variation of WUEe. To quantify the effect of climate change on the variation of productivity of terrestrial ecosystem, the concept of elasticity was used. Here, climate change is represented by the change in Aridity Index (AI). The results showed that WUEe is higher in lower Himalayan ranges and northeastern India (value as high as 3.417 g C/kg H20) having shallow WTD, covered by forest and having tropical wet and humid subtropical climate, whereas it is lower (value close to 0) in northwestern India having deep WTD, covered by shrublands and having arid climate. In spite of occurrence of deep WTD, shrublands in arid regions were observed to be more dependent on groundwater and more sensitive to the conditions of aridity as compared to the vegetations existing in water surplus regions, as the results showed a declining trend of WUEe and an increasing trend of εWUE with increase in WTD. It was observed that there exists a high positive correlation of NPP, ET and WUEe with percentage irrigation in croplands present in water deficient regions and negative correlation was observed in croplands present in humid areas. This study gives us an insight into the interaction between the groundwater and the productivity of terrestrial ecosystem, thus supporting the reasonable management of groundwater across the country of India.