The intra-seasonal variation in precipitation isotopes shows a characteristic declining trend over northeast India. As of now, no mechanism offers a consistent explanation of this trend. We have performed the isotopic analysis of precipitation (rain) and estimated net ecosystem exchange and latent heat fluxes using an eddy-covariance system in northeast India. Additionally, we have used a diagnostic model to determine the recycled rainfall in this region. We find a strong link between the enhanced ecosystem productivity and isotopic enrichment in rainwater during the premonsoon season. Subsequently, on the advent of monsoon, the Bay of Bengal generated moisture enters this region and depletes the isotopic values. Additionally, the regional-scale convective activities produce periodic lows in the precipitation isotopes. Contrary to the general understanding, our study shows that the internal factors, such as the local land-atmosphere interactions, rather than the external influences, play a significant role in governing the precipitation isotopes in northeast India.

印度东北部降水同位素的季节内变化呈现出特征性的下降趋势。到目前为止，没有任何机制可以对这一趋势提供一致的解释。我们使用印度东北部的涡度协方差系统对降水（雨）进行了同位素分析，并估计了净生态系统交换和潜热通量。此外，我们使用诊断模型来确定该地区的循环降雨。我们发现在季风季节增强的生态系统生产力和雨水同位素富集之间存在密切联系。随后，随着季风的到来，孟加拉湾产生的水分进入该地区并耗尽了同位素值。此外，区域尺度的对流活动产生了降水同位素的周期性低点。