Intraseasonal variability of terrestrial biospheric CO2 fluxes over India during summer monsoons.

Abstract

AbstractThe intraseasonal oscillations (ISOs) in terrestrial biospheric fluxes of carbondioxide (CO2) over the Indian subcontinent were investigated for the summer monsoon season from June to September. We utilized two optimized datasets of Net Ecosystem Exchange (NEE) fluxes of CO2 at a spatial resolution of 1° × 1° grid and at daily time scale for the years 2000–2009. Seasonally, over the whole of Indian subcontinent, terrestrial biospheric CO2 fluxes were found to be a net source (sink) during June and July (August and September). Intraseasonal variability of CO2 fluxes for the two distinct time scales, 30–60 days and 10–20 days, was extracted with a spectral harmonic filter. The dominant ISO mode in the CO2 flux over India is at a period of 60 days or longer during weak monsoons years but at 10–30 days for strong monsoon years. The ISOs of CO2 flux show coherent structures along with corresponding rainfall ISOs at a 2–3 day lag (CO2 lags rainfall) and nearly 3–4 day lag with ISOs in surface air‐temperature (CO2 lags air‐temperature). The ranges of these lags are consistent in the two data products examined here. The apparent lags between CO2 flux and rainfall ISOs are found to be induced by the temperature effects on net primary production (NPP) and ecosystem respiration (RE). The terrestrial biospheric fluxes over the subcontinent are coherent with the northward propagating summer monsoon ISOs albeit as a combination of rainfall, available radiation, and air‐temperature. The study offers a mechanistic understanding of variability of terrestrial biospheric sources and sinks of CO2 over the Indian subcontinent, in tandem with the intraseasonal variability of the summer monsoon rainfall.