USA There have been many discussions recently on this website, in the scientific community, and in the more public arena about why the number of acres burned in wildfires has been increasing rapidly over the last several decades. From the mid-1980s through 2015 theaverage number of acres burned has grown from about 2 million acres a year to around 8 million. Some people like to claim that this was caused by climate change, environmentalists preventing timber from being harvested, or other factors. However, to complicate the issue,some data appears to indicate that between 1920 and 1950, 10 million to 50 million acres burned each year.
It is very difficult to say that one factor caused fire occurrence to change. While comparing acres burned in the early part of the 20th century to what we are seeing in recent decades, many variables need to be considered:
Weather and climate trends. This has been vigorously discussed in many venues.
The capacity to suppress wildfires. In the first two-thirds of the 20th century the ability of land managers to suppress wildfires was very different from what we have today. Fire engines now carry many times more water, and transportation systems enable quicker initial attack response. Helicopters and air tankers were brought into the equation. Heavy equipment became more prolific and capable. More efficient communication and dispatch systems were created. Fires are detected more quickly. Firefighters are routinely brought in from hundreds or even thousands of miles away.
The wildland-urban interface is growing. More people are living and recreating where previously there was less human activity. This can increase the number of fire starts, and the endangered structures often have an effect on the priorities of firefighters and where they are deployed, as opposed concentrating forces where they are most likely to contain the fire.
Changes in how timber is managed and harvested.
Fire suppression can result in longer fire return intervals and increases in the amount of fuel available for the next fire.
Fuel treatments: mechanical and prescribed fire.
Changes in the vegetation: non-native species, insects, disease.
Accuracy of the fire occurrence data. Can the data for 1920 be compared with the data from 2016? The fire occurrence data at NIFC for 1962 through 2015 shows a huge swing beginning in 1983 and 1984, with the number of fires overnight dropping by about 50%, a trend that continued through 2015. This leads one to lose confidence in the data. One would think that the more modern era, post 1984, would have more accurate information than previous decades.
Changes in wildfire management policy: full, limited, or no suppression.
Our readers will probably suggest even more factors that affect the number of fires and acres burned.
Considering all of these variables, I am skeptical of reports saying that just one is responsible for changes in the number fires and acres burned.
Winters have started approaching the northern region of India that also includes Delhi-NCR along with Punjab and Haryana. Due to this, minimums have also started dropping in many parts of North India including Delhi and NCR. In fact, as per the temperatures recorded on October 15 and October 17, the minimums ofDelhi and NCR went down to 17°C.
As per experts, an increase in the pollution level normally occurs during the winter months. However, there are a few reasons that could enhance the pollution level in Delhi and the adjoining areas. The very first reason that can be attributed to an increase in pollution level in the national capital is crop fires in the neighboring state ofHaryana andPunjab.
These two states lie in northwest proximity of Delhi and normal pattern of winds during this season is northwesterly. These winds drag the smoke and fine particles of the burnt crop and mix them with Delhis atmosphere. Moreover, the temperatures also start dipping, therefore, the air near the earths surface tends to condense leading to formation of haze.
Whenever the winds are light or calm, these air pollutants get mixed with the haze or mist and forms a blanket of smoke haze which remains suspended for few hours in the mornings. Thereafter, the haze disappears as the sun rises and temperatures increases during the day.
But as the winter progresses in the month of December and January, the duration of haze, mist or fog gets extended and these pollutants remain suspended in the atmosphere for longer duration of time. Other factors including the smoke emitting from vehicles and factories and dust from construction sites also add to the rising pollution levels.
Sometimes this situation can continue for days altogether. However, relief is expected only when a strong Western Disturbance gives rain over the region. It is then that these pollutants settle down for a few days.
Another criterion which reduces the pollution levels is the strong and moderate dry winds from northwest or west which carry away these pollution particles. In a nutshell, it can be said that in October, intensity and duration of pollution remain less though increases in November as winters sets in.
– See more at: http://www.skymetweather.com/content/weather-news-and-analysis/delhis-pollution-level-increases-as-winter-approaches/#sthash.FRlJsEib.dpuf