Monsoon Disturbance and Its Impact
[WTN-L World Tibet Network News. Published by The Canada Tibet Committee. Issue ID: 02/09/09; September 9, 2002.]
By Dr. Mirza Arshad All Beg Dawn
Pakistan has been facing drought conditions for the last six years. The following analysis shows that the combined effect of a number of factors has brought about a change of an irreversible nature in the monsoon system which governs the climate of the South Asia region.
According to Pakistan Meteorological Services, the drought conditions may continue till December 2002 or even later due to El-Nino and La-Nina factors and sub-tropical heights which could affect the wheat crop of this year. It has been argued that El-Nino and La Nina factors have upset the system of rains in India, Pakistan, Iran and Afghanistan. Incidentally El-Nino events are a local manifestation of a global phenomenon, which begins with the relaxation of the wind stress that drives warm water towards the west. In the case of the monsoons, which are also part of a global phenomenon, the atmospheric pressure at sea level at the south-west of the Indian Peninsula, the ocean temperature in the Bay of Bengal and the rainfall fluctuation across South Asia are inter-related critical factors.
Precipitation over major areas of Pakistan and snowfall in the catchment areas of the Indus and its tributaries has been low for the past six years, due perhaps to the adverse impact of the dominant La-Nina factor operating over the Bay of Bengal; it can be the reason for the flood flows in Brahamputra that inundates Bangladesh and for the Indus to run dry. The two rivers, it may be mentioned, bring snowmelt to Tarbela and Mangla dams respectively but both have been running with nominal flows until May over the last six years. The two events repeat themselves after three to five years with variable intensity. Since their duration in coming back to normal has been much longer, there have to be reasons other than just the selective heating of the seawater.
Some of the reasons that immediately come to mind are related to human activities that may have induced modifications in the monsoon pattern. This author had argued in these pages last year that the precipitation across the Himalayas in Tibet and over the catchment area of the Brahamputra is much larger than the Indus perhaps because the monsoon winds are able to cross over unrestrained by the high mountains. The Brahamputra has the same source as the Indus viz. Mansarower Lake over Tibet. It has received repeated flood flows for the last few years while the Indus has been running nearly dry. There was only one flood flow till late August this year and that too of low intensity.
Initiation of the monsoon in the first week of June at the tip of the Indian Peninsula followed by its crossing it over and entry into the Bay of Bengal has not changed during all these years. A major change was, however, noticed this year in the intensity and impact of storms over the Bay of Bengal. The entry of the monsoon winds into Bangladesh and the rainfall there otherwise followed almost the past pattern. Some drastic change has definitely occurred in the ecosystem in the north of Bangladesh since the monsoon winds instead of going west are, for the last four years, crossing over the Himalayas.
It is not just a coincidence that floods of high intensity were witnessed this year as well as in 1998 over vast stretches of mainland China from the far western province of Xinjiang, to Shaanxi, Sichuan and Guizhou provinces in the west, to the densely populated agricultural provinces of Hunan, and Jiangxi in the central region. The deviation is related to the formation of an extensive low pressure area in the north of Tibet. It may be pointed out that the ecosystem of the mountainous northwestern areas of Shaanxi has, during the years of development, been extensively degraded due to deforestation.
The heat engine of this extended area that governs the monsoon system in China has the enhanced capability to draw moist air from the system that is across the Himalayas at Bhutan and Nepal. This system forms at the same time as that in South Asia as is visible in the weather map of June 4, 2002. This explains the phenomenon that brings rains over the catchment area of Brahamputra in Tibet and contributes to flood flows of tributaries of the mighty Yangtse. It is this deviation that does not allow massive precipitation in the region west of Nepal.
The situation was grim in the east of Nepal, with nearly 42 million people affected in Assam and Bihar states in India. Most of the 250 rivers of Bangladesh originate in the Himalayas and run through India before draining into the Bay of Bengal. Incessant rains and overflowing rivers have engulfed vast areas, killing 157 people since June, 2002. Heavy monsoon rains in Nepal triggered flash floods and landslides. The latest occurred in August, when a huge landslide struck the remote mountain village of Thapra in Ramechap district in eastern Nepal.
It is more than likely that the main factor responsible for the deviation that has caused rains across the Himalayas and on the east of Nepal but not on its West, is the ecosystem change due to indiscriminate exploitation of forest resources in the eastern Himalayas. This has besides causing landslides in Nepal and the eastern states of India, set the stage for alteration of the monsoon pattern in South Asia. The monsoon winds are now crossing over the Himalayas into China, instead of travelling along the mountains and bringing rains to the Lower Himalayan region over Nepal, and Uttar Pradesh, the northern areas and later on to the southern areas of Pakistan.
This year all the six or seven monsoon storms, including the one that is visible from the satellite picture of June 4, 2002, that entered Bangladesh from the Bay of Bengal crossed over into China and aided to the flood flows of the tributaries of the Yangtse. On the contrary there was only scant rainfall in the Lower Himalayas, and northern as well as southern Pakistan. This change in the monsoon pattern, apparently caused by deforestation of the Himalayas is likely to have devastating consequences. It will reduce the precipitation over the northern areas and limit the flow in the Indus and Jhelum to less than 80 maf. The end result will be massive desertification of southern and western areas of Pakistan.
A change in pattern also appears to have occurred in the western system that brings moisture laden winds to the western and northwestern part of Pakistan during the winter for the rabi crops. At least five or six storms cross over into Pakistan during winter. Precipitation from this system is aided by the high pressure zones over the Pamirs and the north of Afghanistan. This year (November to February 2002) the high pressure area did not shift to the north of Afghanistan but remained right over this territory. This reduced the cross-over of the storms into Pakistan to only two and that is why the barani area of the north could not produce the winter crops. If our wheat target was short by a few hundred thousand tons, it was because this area could not contribute to crop production.
High pressure zones, such as the one that formed over Afghanistan, are formed when the concentration of particulate matter in air over land is high. Particulate matter in high proportion causes cooling of air and are cause for creation of high pressure zones that can push moisture laden winds away from the area. The particles being small in size tend to suppress rainfall because the water droplets that condense on them are light enough to remain upward. Carpet bombing was so intense in Afghanistan during the critical period when the winter storms cross over into Pakistan that the air over the entire territory must have raised the level of particulate matter beyond critical limits. As such the storms just could not reach Pakistan. The weather satellites were recording the diversion of the winds and the results were being telecast each night on PTV.
It might be interesting to note that climate change of similar nature was also noted when Hiroshima and Nagasaki were destroyed by atomic bombs. Temperature of the macro-environment recorded a rise and the macro-climatic conditions had changed.
Yet another factor that may be responsible for the observed climate change is the sulphate aerosol induced fog that is observed during winter over the area from Multan to Islamabad, There is an annual slow down of economic activity for at least five weeks due to the fog that has its origin in the said region in India. The Brown haze observed over South Asia reduces solar radiation over the concerned areas and thus reduces availability of moisture in the air. This has aggravated the impact of climate change. The root cause of the brown fog is sulphur dioxide, nitrogen oxides and particulate matter emitted by foundries and other industrial units using coal as fuel in the region extending from Bengal and Bihar to Uttar Pradesh and Gujrat in India. These emissions are likely to multiply with increasing use of coal towards intensification of industrial activity in India.
The factors just mentioned show that climate change has come to stay. Degradation of the Himalayan ecosystem does not appear to be reversible. Accordingly it will not be wise to depend on the eastern system of monsoon. It may be possible to cash on the system developing in the western coast of India that brought rains in late August this year and late July last year, but this will require intensive vegetation over the Nokundi-Sibbi-Jacobabad axis that presently forms the heat zone of the eastern system of monsoon.
In view of the half-hearted attempts at forestation, this seems to be a far-fetched idea. Moreover there is no likelihood of water being available for plantation of trees and hence the plan may not be implemented at the outset.
The impact of climate change on the economy, particularly agricultural activity, will nevertheless be highly disturbing since water availability will be reduced to below 90 MAF. The availability at canal head was, according to Economic Survey of Pakistan, 2001-02, less than 84 MAF. This will go down still further. Availability from tube wells will go down each year since the groundwater sources will not be adequately charged.
The above analysis paints a gloomy picture and presents a worst case scenario, which deserves serious consideration. Pakistan has already lost time in adopting conservation practices. It is now time only for crash programmes to save on water and to live with a limited budget of less than 90 maf.
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