Rain in Darjeeling

The LOcal and Remote influences on Rainfall over India (LORRI) project is investigating the impacts of short-lived air pollutants on climate and rainfall in South Asia. 

Climate change and air pollution are closely linked issues, and understanding their interactions is central to Earth system research. Emissions of gases and aerosols not only degrade air quality, but also affect the radiative balance of the atmosphere, driving global and regional climate change.

What are SLCPs?

We measure the strength of different greenhouse gases by their contribution to what is known as 'radiative forcing'. This is a measure of the energy imbalance between the incoming solar and outgoing infrared radiation at the top of the atmosphere caused by the greenhouse gases and aerosols. Short-lived climate pollutants (SLCPs) such as ozone, sulphate and carbonaceous aerosols (small particles resulting from the buring of fossil fuels) have inhomogeneous distributions, and thus the radiative forcing that they exert is complex. Recent studies suggest that forcings from SLCPs can be of comparable importance to forcings from long-lived greenhouse gases (e.g. CO2), with a heavy dependence on the location and the type of the forcing.

Air pollution and the South Asian Monsoon

Monsoon rain in Kolkata The local climate in South Asia, and in India in particular,  is strongly influenced by SLCP emissions, especially anthropogenic aerosols. Furthermore, this region is one of the most highly populated parts of the world, while its economy, levels of human health, and ecosystem sustainability heavily depend on the amount of rainfall received annually.

Most precipitation in this area falls as part of the South Asian Monsoon, a phenomenon that is not just critical for human life and ecosystems, but also very challenging to study and understand. The South Asian Monsoon is also a central aspect of the global climate system, and so is key in understanding global and regional climate change.

Observations have shown that monsoon rainfall has decreased in the region over the past few decades. Some recent studies have discussed the possibility that anthropogenic aerosols may be the cause of such changes. However, this hypothesis has not been tested thoroughly, and it is still debatable whether local or remote sources of aerosols are more important.

Project aims

The main objectives of LORRI are:

  • To investigate the climate impacts of aerosol and tropospheric ozone precursor emissions over South Asia, and how they compare to the impacts of longer-lived species such as CO2. Particular focus will be placed on remote influences.
  • To understand the physical processes linking regional emissions with radiative forcing, and local and remote climate response, with a particular focus on rainfall
  • To suggest which combination of local and remote emission controls can have the optimum impact on Indian climate and air quality

UKIERI logo

 LORRI is a collaboration between Imperial College London and the Divecha Centre for Climate Change. It is funded by UKIERI

Publications

Chakraborty, A., Nanjundiah, R. S. and Srinivasan, J. (2014), Local and remote impacts of direct aerosol forcing on Asian monsoon. Int. J. Climatol., 34: 2108–2121.

Blog: It’s a small world: How air pollution in Europe can affect rainfall in India