Remote sensing-based multi-scale characterization of ecohydrological indicators (EHIs) in India

Abstract

The carbon, water, and energy cycles play an important role in the terrestrial ecosystem's functioning. Climate change and hydroclimatic disturbances are primary factors that influence these cycles, yet little is known about the major ecohydrological indicators (EHIs) that characterize these cycles. In addition, it is essential to analyze spatiotemporal variations and driving factors of EHIs to comprehend how well terrestrial ecosystems can preserve their structure and function in the face of hydroclimatic perturbations. We assessed the three important EHIs, namely water use efficiency (WUEe), rain use efficiency (RUEe), and light use efficiency (LUEe), as well as their controlling factors, in India from 2002 to 2017 at various spatial scales (major river basins, climatic zones, and land cover types). In general, high EHI values were found in high productivity ecosystems (e.g., forest ecosystems) compared to low productivity ecosystems (e.g., cropland and grassland ecosystems). WUEe and LUEe have similar characteristics and were higher in mountain, tropical wet, and tropical wet-dry zones, whereas lower in arid zones. RUEe shows distinct spatial characteristics with higher values in semi-arid zones and lower values in arid zones. The drivers investigated in this study include CO2 concentrations, evapotranspiration (ET), humidity, leaf area index (LAI), normalized difference vegetation index (NDVI), precipitation (PRECIP), soil moisture (SM), solar radiation (SR), temperature (TEMP), vapor pressure deficit (VPD), and wind speed (WS). All three EHIs were found sensitive to TEMP and SR at a national scale, whereas CO2 was a significant driver in arid ecosystems. Other controlling factors (e.g., VPD, SM, and humidity) also played a significant role at smaller spatial scales. Further, this study finds that undisturbed ecosystems (only climate influenced) have slightly higher values of EHIs compared to disturbed (climate-human influenced) ecosystems. Based on the results, in future, it can be expected that an increase in the incident SR and TEMP will decrease the EHIs in India. This study helps understand the coupling of water, carbon, and energy cycles, and the findings from this research can be a reference for ecosystem conservation and restoration.