Atmospheric Physics and Convection, NISER

Convective control from forests in the Himalayas with in-situ measurements and numerical atmospheric modeling

Hill communities in western Himalayas have reported the loss of their native broadleaved forests of Oaks to native but colonized forests of Chir pine. This transition is frequently related to both plantation and climate warming. This change has immense sociological impact because the Chir, in contrast to Oaks, is known to foster drier conditions which are related with reduced stream flows and eco-system services and loss of biodiversity.

In this project we are investigating the climatological impacts of Chir versus Oak forests. The study involves both intensive field data collection and numerical atmospheric simulations.

We have found a significant down-regulation of transpiration by the Oak forest in almost all seasons as compared to the Chir forests which transpire vigorously throughout the year in all age classes (figures below). This is supported by our hydrological measurements which also indicate a smaller evapotranspiration in the Oak forest (figure below).

The group is currently utilizing these observations to simulate the disparate impacts of these forests on local convection, clouds and precipitation in the region.

Doctoral and Post-Doctoral positions are available. Please get in touch!

AGU 2023 AGU 2024 Bowen Ratio Measurements AGU 2024 Transpiration Measurements

Banj Oak versus Chir Pine, western Himalayas

Numerical simulation of regional climate over the Himalayas using the Ocean-Land-Atmosphere Model

Evapotranspiration and heat flux from the Pine (top) and Oak (bottom) measured with the Bowen ratio method

Transpiration in Pine (top) and Oak (bottom) trees of various girth classes as measured using sap flux sensors

Cumulative progression of rainfall, runoff, baseflow and stormflow at the Pine (top) and Oak (bottom) forests

Indirect negative correlation between surface temperature and near surface humidity (blue shading)

Distribution of low, mid and high level clouds across the ITCZ and its correspondence with corr(T,q) (black curve)

Meteorological variables during the May 2016 severe heat wave in India. Highest surface temperatures (red curve) correspond to a period of lowest atmospheric humiidity (red shading)

An indirect counter-greenhouse effect of water vapor mediated by low-to-mid level clouds

Severe pre-monsoonal heat stress has become a routine occurrence in several tropical regions. During this season of high heat stress, we have found a surprising indirect, radiative surface-cooling effect of water vapor during periods of high ambient humidity in the pre-monsoonal season. This observation is contrary to the strong greenhouse effect generally associated with water vapor. We show that this radiative surface-cooling is associated with a previously unreported large positive correlation between lower tropospheric humidity and cloud cover in these regions. This indirect negative radiative effect of water vapor is particularly relevant for heat stress during the pre-monsoons, as demonstrated by a case study of May 2016 heat wave over the Indian sub-continent when this phenomenon is found dominantly active throughout the season and in its warming phase during the period of the heat wave.

Doctoral and Post-Doctoral positions are available. Please get in touch!

ERL Publication AGU 2023 poster EoS preprint

Convection triggered by deforestation in the Amazon rainforest

More than 20% of the Amazon rainforest has been cleared in the past three decades, triggering important hydroclimatic changes. Small-scale (a few kilometres) deforestation in the 1980s has caused thermally triggered atmospheric circulations that increase regional cloudiness and precipitation frequency. However, these circulations are predicted to diminish as deforestation increases. Here we use multi-decadal satellite records and numerical model simulations to show a regime shift in the regional hydroclimate accompanying increasing deforestation in Rondônia, Brazil. Compared with the 1980s, present-day deforested areas in downwind western Rondônia are found to be wetter than upwind eastern deforested areas during the local dry season. The resultant precipitation change in the two regions is approximately ±25% of the deforested area mean. Meso-resolution simulations robustly reproduce this transition when forced with increasing deforestation alone, showing that large-scale climate variability plays a negligible role. Furthermore, deforestation-induced surface roughness reduction is found to play an essential role in the present-day dry-season hydroclimate. Our study illustrates the strong scale sensitivity of the climatic response to Amazonian deforestation and suggests that deforestation is sufficiently advanced to have caused a shift from a thermally to a dynamically driven hydroclimatic regime.

Nature Climate Change publication, NCC News and Views, EoS Coverage

Clouds over deforested regions in 1980s and 2000s, Rondonia, Brazil

Simulated cloud cover over deforested areas in 1980s and 2000s

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