Onset of summer monsoon in Northeast India is preceded by enhanced transpiration

Abstract

Variations in isotopic composition of water vapor in the atmosphere is an important indicator of the processes within the hydrological cycle. Isotopic signature of water vapor and precipitation can be helpful in partitioning evaporation and transpiration fluxes. It is well known that transpiration from forested regions supplies a significant amount of vapor to the atmosphere in monsoon and post-monsoon seasons. Here, we utilize observations from Tropospheric Emission Spectrometer (TES), Atmospheric Infra-Red Sounder (AIRS) and simulation models to ascertain that transpiration is dominant in the forests of Northeast India (NE) during pre-monsoon season. Our results show an increase in δD of 78.0 ± 7.1‰ and in specific humidity of 3.1 ± 0.2 g kg−1 during the pre-monsoon months of April-May compared to January-February. In the monsoon months of July-August, δD reduces by 53.0 ± 6.5‰ albeit the specific humidity increases by 3.4 ± 0.2 g kg−1. Using joint observations of specific humidity and isotope ratio in lower troposphere, we discern the moisture sources over NE India in pre-monsoon and monsoon seasons and posit the role of transpiration in continental recycling during pre-monsoon season.

Annually Resolved Monsoon Onset and Withdrawal Dates Across the Himalayas Derived From Local Precipitation Statistics

“…However, for water availability and management, the premonsoon period may have considerable importance, especially because it coincides with the start of the vegetative season. Previous work relates premonsoon rain to surface water availability and evaporation in the Indo‐Gangetic plain (Pradhan et al, 2019; Tuinenburg et al, 2012), consistent with the relative isotopic enrichment of premonsoon rainfall (Figure 1c). This has increased substantially in recent decades due to extensive irrigation (Cook et al, 2015; Rodell et al, 2009; Tuinenburg et al, 2014).…”

Interannual Variation of Transpiration and Its Modeling of a Larch Plantation in Semiarid Northwest China

“…Quantifying plant transpiration (T) variation is important for not only the estimation of a water budget but also the elucidation of the role of T in an energy budget, the effects of hydrological flows on vegetation production, and ecosystem responses to climate change [14][15][16][17]. Tree T, which utilizes a large proportion of forest evapotranspiration [3], is a key factor affecting the stability and services of forests, and the regional water balance, or even water supply security [13,[18][19][20].…”

Influence of climatic indices (AMO, PDO, and ENSO) and temperature on rainfall in the Northeast Region of India

“…The seasonal rainfall variability over this region is mainly due to the Indian monsoon system. The heaviest rainfall events during the pre-monsoon season over this region have suggested to associating with the thunderstorm or local convective activities [20,31]. The increasing heaviest rainfall events during the monsoon season are some extent associated with the Madden-Julian oscillation [21].…”

“…In the high-frequency area, phase difference at 12 months is almost 0°, i.e. the increasing temperature tends to enhance water vapour in the atmosphere, which arises from open water bodies and vegetation present over this region [31] and also due to glacier melting in the high Himalayas causes convective lifting leading to rainfall. However, the phase difference at 6 months is unstable, i.e.…”

“…Understanding the rainfall variability over this region is of particular interest to many researchers from the perspective of agriculture and water resources management. Several researchers reported that the low-pressure area during monsoon season [28][29][30], local thunderstorm activity [20], and western disturbances [31,32] are the primary weather system, which is responsible for rainfall variability over this region. Several studies have also noted the statistically increasing/decreasing rainfall trends in monthly and seasonal scale over this region [33][34][35][36].…”