VEGETATION ATMOSPHERE COUPLING

Although not apparent, vegetation can significantly regulate its immediate climate through for example – atmospheric regulation of CO2 (photosynthesis), moisture (evapotranspiration) and energy (by absorbing solar radiation). However, under what conditions does this regulation become detectable on climatic scales? We investigate these questions in the forests of the Amazon and the Himalayas using numerical modeling and, since recently, field data collection.

Clouds over deforestation, Rondonia, Brazil

DEFORESTATION IN AMAZONIA

Deforestation in the Amazon rainforest has happened over patches of a few hundreds of kilometers – the size of Uttar Pradesh amidst a tropical rainforest the size of two Indias. Most of this deforestation is for cattle ranching fueled by the globally increasing demand for meat.
What impacts does this extremely large scale, patchy deforestation have on local climate? We ask this question because decades of research has shown that the rainforest produces at least one third of its annual precipitation through local evapotranspiration. Hence, clearing a large patch of forest can be consequential for local hydroclimate.
Surprisingly, the rainforest is so resilient that deforetstaion at scales even as large as contemporary scales does not have a statistically detectable impact on monsoon season precipitation. However I showed through my research that during the dry season there is a statistically significant impact on the spatial distribution of precipitation over the deforested patch – more precipitation in the downwind deforested regions and less precipitation in the upwind deforested regions. Numerical experiemnts with atmospheric models show that this observed redistribution of precipitation is due to the generation of atmospheric circulations over the deforested area owing to the reduction in vegetation height.


CLIMATIC IMPACTS OF NATURAL VERSUS COLONIZED TREE SPECIES IN THE HIMALAYAS (ONGOING)

Hill communities in Western Himalayas have reported the loss of their hydrological resources due to the replacement of broadleaved forests by native but colonized pine forests of Chir. The colonization is traced back to the British to utilize Chir for its various industrial uses. However, the Chir is now supposedly overtaking the once abundant broad leaved forests which anecdotally also conserve the local water table, unlike Chir.
In this project, in collaboration with hydrologists, we are investigating whether pine forests of Chir, as compared to broadleaved forests of Oak, have a negative impact on the local hydrology and hydro-climate.
The study will involve both field data collection and numerical investigations of the local hydro-climate as coupled with the local vegetation.

JRF and RA positions available. Please contact Dr Khanna at jkhanna@niser.ac.in

Banj Oak versus Chir Pine, native species in western Himalayas

Clouds over deforestation, Rondonia, Brazil

VEGETATION-CONVECTION COUPLING IN AMAZONIA (ONGOING)

Coming soon…


LARGE SCALE CONTROLS ON REGIONAL CLIMATE

Coming soon …

Natural Spring, Uttarakhand

GROUND WATER RESOURCES AND CLIMATE CHANGE IN WESTERN HIMALAYAS (ONGOING)

Anecdotal evidence suggests that underground water resources in the Western Himalayas are on a steep decline. This has specifically impacted ‘Natural Springs’, which are natural underground waters jutting out from the surface through fractured rocks which connect to the water aquifer. Hill communities, which dwell on higher slopes of mountains are specifically dependent on these mostly perennial springs for their fresh water needs. Declining or drying springs have posed a major challenge to these hill communities and local and state government bodies. This has triggered major initiatives from the Government to investigate and remedy this societal issue.
In this project we are investigating a variety of hypotheses which could lead to a degradation of these perennial water resources. At my lab we will be investigating the role of climate change induced precipitation changes as a potential cause for the decline or drying of spring waters in the state of Uttarakhand, India. The project has a major part of field data collection. At my lab we will analyze the field collected data and numerically investigate climate change signals over the hills.

Open Institute PhD positions available. Please apply.


REGIONAL GHG-INDUCED WARMING IN TROPICAL FORESTS

Do wet and dry climates respond similarly to Green House Gas induced climate warming? i.e. do such regions show the same amount of GHG-induced surface warming? Note that GHGs like CO2 and CO are quite uniformly distributed in space hence expecting a regionally different surface-warming response is quite counter-intuitive. Nevertheless, regionally disparate responses are robustly observed.
In this project we investigated if the presence of soil moisture can make a region less susceptible to GHG-induced surface warming due to the cooling action of evaporation. We found that this relation is true in most large dry areas within the subtropics – Sahara, southern Africa, Australia (blue colors in the figure). However, and very counter-intuitively, the wet regions within the tropics, like the Amazon rainforest, show an amplified warming in regions with higher soil moisture. We found that the governing process is possibly connected with the abundance of clouds in these high soil moisture regions, which results in a positive radiative effect, trapping the outgoing longwave radiation, hence amplifying the GHG-induced surface warming.

Increased surface warming (red) possibly due to high clouds in tropical forests

Severe heat wave that hit Hyderabad, India in 2015.

WATER-VAPOR, AEROSOLS AND HEAT WAVES (ONGOING)

Coming soon …

Open Institute PhD positions available. Please apply.

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