Investigation of scale interaction between rainfall and ecosystem carbon exchange ofWestern Himalayan Pine dominated vegetation

Abstract. Forests of the Western Himalaya, India, are impacted by the summer monsoon and winter seasonal rainfall events and associated changes in the meteorology. Here, we assess the scale interactions between observed forest ecosystem fluxes and meteorological parameters, particularly rainfall seasonality and extremes. The scale interactions were investigated using daily observed fluxes and meteorological parameters of 1080 days of 2014–2016 from a Pinus roxburghii dominated forest and using wavelet spectral analysis method. The mixed forest of this study was a sink of CO₂ having the average NEE −3.21 gC m⁻² day⁻¹ for the period of observations. Result of the wavelet coherence analysis from observed data indicated a statistically significant correlation (> 0.7 at 95 % confidence level) between daily average NEE and daily total rainfall having band periods of 70–120 days, 35–64 days and 60–90 days of monsoon periods of 2014–16, respectively, where rainfall leading to NEE. Impact of heavy rainfall events of monsoon periods over NEE of the forest patch was found to have average band periods of 4 days; whereas, the winter time heavy rainfall events were having average band periods of 15 days with very high local correlation (> 0.7 at 95 % confidence level) inferring that ecosystem exchange rate was mirroring rainfall events. Although CASA-GFDE3 model simulated daily NEE values of 2014–15 were found have a low fraction of explained variance (= 0.08) with respect to observations, modeled NEE-rainfall relationship of 2014 was found to corroborate well with the observed pattern; however for 2015, the phase relationship between modeled NEE and rainfall around band period of 100 days was opposite to the flux tower observations. Subsequently, heavy rainfall events and daily average air temperatures were also found to be coherent during monsoon period having wavelet coherences > 0.8 indicating a cause and effect relationship between both parameters, and rainfall events were mirroring temperature variations. Therefore, it is anticipated that the Pinus roxburghii dominated forest productivity of Western Himalaya, India, are expected to increase even with the increment of heavy rainfall events in the near 20 future.