Friday, January 6, 2017

Trend of Fires Over Northern India and Pakistan During The Last Decade 

The monsoon season (July – September) is the time when good rains aid rice cultivation in the northern states of India. Monsoon starts receding from North India in the beginning of October. Rice is harvested and then during October-November the crop-residue is burnt to clear the agricultural land and prepare it for the next crop. Fires set for clearing large portions of land results in huge amounts of smoke (or PM2.5) that gets transported to the Indo-Gangetic Basin (IGB) by north westerly winds. Air quality deteriorates significantly in the entire IGB region.

Smoke over IGB can be clearly seen in true color (RGB) satellite image (Figure 1) from October 30, 2016 taken over Northern India by VIIRS instrument. The red dots in the image are the fire locations, most of which are in the state of Punjab. Smoke transported over north indian states can be easily seen in the image. Mapping of all the fires observed by the MODIS satellite instrument (Figure 2) shows that majority of the fires during October 1 - November 18, 2016 are located in Punjab (see orange dots).

The number of fires over northern India and adjacent Pakistan region [23-35 N ; 70 - 85 E) during Oct-Nov months (Figure 3), as detected by MODIS between 2005 and 2016, shows some interesting features.  The total number of fires during the two months show some variability from year to year but there is no clear trend of increase or decrease in the number of fires. Fire count during 2016 are definitely higher than 2015. Note that 2016 fire count data are preliminary and only upto 18 Nov, 2016. More interesting is the shift in the crop residue burning month.  From 2005 to 2011 (barring 2010), the number of fires in October exceeded those in November. There is a substantial difference in October vs November fire counts between 2005-2008 ; the differences reduce thereafter. From 2012 to 2016, the number of fires during October are less than fires in November; with fire count differences increasing between the two months.

Increased fire activity points towards deteriorating air quality conditions that adversely impact human health conditions. The shifting pattern in the burning season, on the other hand, is an indicator of a shift in regional climatic conditions and perhaps the growing and monsoon season itself.