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Dr. Mirza Arshad Ali Beg
IMPACT OF CLIMATE CHANGE ON WATER BUDGETPresented at SAREAA Conference, Dhaka, Nov. 2000 Dr. Mirza Arshad Ali Beg Former Director General (P&D) PCSIR 136-C Rafahe Aam Housing Society, Malir Halt, Karachi-75210
ABSTRACT
The process of recurrent failure of the monsoon system in completing the western segment of its cycle, incidence of heavy rains in its eastern segment each time accompanied by devastating floods, in the intensity of heat wave, erratic nature of precipitations, snowmelt and river flow since the early 1990s, and the drying up of Hub dam has been described and its impact on water budget examined. It has been observed that the year 1992 was erratic in being too wet, 1993 in being dry and that since the mid-1990s the monsoon system, though fully operational up to mid-August on the southern, eastern, and central regions of its cycle that include India and Bangladesh, loses its intensity as it reaches central India. Precipitation on the east of Lake Mansarowar, the catchment area for Brahamputra was heavy and either the winds slackened so as not to reach the catchment area of Indus on the west or there was not enough moisture in the clouds or snow cover left to contribute to the flow. The system besides failing this year also started to recede in Nepal around the same time. Heavy downpour in September in West Bengal flooded extensive areas, including Bangladesh, while Islamabad received only 22 mm rainfall from the same system.
Deforestation and desertification have extended the heat zone to the northern areas where the temperatures are now reaching 42oC during summer, and large dams and diversion of river flow into an intricate irrigation system have increased the losses due to seepages, evaporation and evapotranspiration and the consequent increased availability of water vapour, a greenhouse gas in the air. Explanations for climate change have, besides the above man-made interventions, been sought in terms of cycles of wetness and dryness as done by Shnitnikov’s analysis, and in the persistent domination of El Nino and La Nina factors that are a local manifestation of global events.
Key words: Climate change, Monsoon systemIntroductionClimate change issues emerge as a result of changes in the ecosystem caused by natural or man-made degradation that may have persisted in the microenvironment and macro environment during the course of several years. The change is noticed as an abnormality in (i) increase or decrease in the mean maximum and minimum temperature, (ii) rainfall and/or snowfall, cloud cover, and receipt of solar energy, (iii) availability of water from surface run off and groundwater extraction, and reduction in the water level of the aquifer, (iv) rise in sea level, or loss/gain of land area to/from the sea, (v) loss of natural habitat (vi) loss of vegetative/forest cover, (vii) loss of biodiversity, (viii) extent of production and consumption of greenhouse gases, including water vapour, etc. Such changes occur invariably in the arid regions of the earth that have a surplus heat budget and are worst affected by impoverishment of resources, mainly water. They have a short as well as long term effect depending on whether the changes are confined to the micro and macro environment, or to the global environment. They are of permanent nature if their impact is on the global cyclic events.
Some of the abnormalities just mentioned have appeared in the form of recurrent failure of the monsoon system in completing the western segment of its cycle and widespread precipitation of moisture in its eastern segment with heavy rains causing devastating floods each time. Abnormalities are being noticed in the magnitude and intensity of heat wave but not in the range in the mean maximum and mean minimum temperature and in the erratic nature of precipitation, snowmelt and river flow since early 1990s1.
It has been observed since the mid-1990s that the monsoon system is fully operational up to mid-August on the southern, eastern, and central regions of its cycle that include India and Bangladesh but it loses its intensity as it reaches central India. The system failed this year again to reach the northwest and western ends of its cycle and had also started to recede in Nepal around the same time. The western and northwestern regions of India and Pakistan received very little rainfall thereafter but heavy downpour in September in West Bengal flooded extensive areas and affected 17 million people there, including the low lying areas of Calcutta. Pakistan received only scanty rainfall from the same system, with Islamabad getting 22 mm and other areas in the vicinity receiving scattered showers. The rainfall was so scanty that it could not cause flood and this was the first year in the history of Sukkur Barrage that flood-flow was not received by the Indus. Scanty rainfall has adversely impacted the aquifers of water-starved regions all over Pakistan. Since it takes several years of adequate rainfall to recharge the groundwater resources and several hundred years if left to the natural process of surface water infiltration, it is likely that depletion of aquifers is a local manifestation of irreversible damage to the environment.
Changes in Ecological Balance Governing Water Resources
A mix of processes involving removal of forest cover, preparing the land and harnessing surface and ground water resources for irrigation and domestic purposes have modified the ecosystem in the area that is now Pakistan. Deforestation in this region has been extensive during the last two centuries when vast areas of the jungles were denuded, but the degradation processes became widespread and almost half of the vegetative cover was removed during the last 25 years.
Geographical location of the country between 24oN and 37oN places it in the heat surplus zone of the earth, which suggests high losses of water from land surfaces due to evaporation and evapotranspiration and large variations in atmospheric pressure from winter to summer is said to be the largest on the globe, with the result that the wind system is completely changed from the trade wind pattern. This has contributed to erosion of fertile soil and desertification. Heating of extensive areas of Kharan, Thal, Thar and Rajasthan deserts, with the intensity of heat focused on the area enclosed by the Nokundi-Sibbi-Jacobabad-Sargodha-Mianwali axis, creates low pressure zones that set the heat engine of the monsoons into motion by causing transportation of moisture laden winds from the surface of the Arabian Sea and Bay of Bengal. Extensive deforestation of the area has enlarged the heat zone and now it extends in the north to the Northern Areas, where temperatures of 42oC have been recorded in Gilgit and in the west to Iran where drought has taken the country into its grip for the last two years. The expansion of the heat zone has thus exposed the glacier areas and caused rapid melting of the snow cover.
A mismatch between availability of water and its extensive use that has increased by almost 250% during the last 50 years, has resulted in withdrawal from all sources viz. rivers, canals, wells, tubewells, karezes and springs1. This type of modification in the ecosystem has increased aridity in the region and has instigated losses of habitat, vegetative cover, biomass and biodiversity2. Construction of large dams, diversion of river flow into an intricate irrigation system and over harvesting of groundwater resources constitutes the greatest intervention of ecosystem of the region, and a large interference in the water cycle by increasing the losses due to evaporation and seepages and the consequent increased availability of water vapour, a greenhouse gas in the air.
Extensive harnessing of groundwater aquifers has assumed the status of mining and that too at an unprecedented rate. It is estimated that almost 10% of agricultural food production is now dependent on mined groundwater. Water tables that were falling at a rate of a metre a year have been going down in many areas at a much rapid rate of 0.5 to 2 metres per year. In Quetta valley, for example it has fallen by 40 metre during the last 30 years3. A similar situation is being faced in China, India, Mexico, Oman and Yemen.
Loss of storage in the aquifers and their mining already indicates that availability of water in Pakistan has decreased and aridity is on an increase. Fluctuations in water table are vulnerable to weather changes e.g. changes in temperature, humidity and rainfall. These changes affect the rate of evaporation and evapotranspiration and also the sub-soil flow. Aridity causes increased evaporation, which in certain cases is in excess of 3 cusecs per square mile in certain worse areas. Evaporation from soil surface is related to the depth of groundwater. It is very high, ranging up to 50% of the surface water evaporation; 20% for a depth of 5 ft and 33 to 55% for a depth of 10 ft .for a groundwater depth of 2 to 3 ft.
The annual rainfall and floodwater seepage constitute the ecological processes that balance the inflow and outflow of groundwater. They have been disturbed by extensive withdrawal and diversion into canals, which leave about 24 billion cubic metre (bcm) for Lower Sindh. The groundwater resources are not being replenished to help in building up the reservoirs of the areas adjacent to rivers and in filling up their sub-soil, or the deep zones of groundwater. The irrigation system has changed the inflow-outflow balance that was being maintained by river flow and flood flow and has been replaced by seepage from canals and distributaries. The losses being of the order of 15 to 25% of the irrigation water supplied have caused a reversal in the flow as groundwater current gets directed from canals to rivers and depressions.
The recharge in the delta area is restricted to area within the embankment system, whose construction was aimed at providing protection against flooding. This constitutes another set of interventions that has caused an irreversible damage to the ecosystem of the riverine and delta areas. The embankments have removed the floodplains and the aquifer there is not being recharged with the same frequency and intensity as in the 1950s. The ecology of floodplains and delta area changed after the mid-1960s, and its adverse and irreversible impacts have, besides depriving the delta area of its traditional rice crop, induced seawater intrusion through intensive harvesting of groundwater5,6.
Past Trend in Maintaining the Water Budget
Pakistan receives its 180 bcm or 145 MAF of surface flow from snow and glacier melt, and from the monsoon system as the main elements of its water budget4,5. The melting of perennial snow cover and glaciers in the Lesser Himalayas, which are the south oriented outer ranges of the Himalayas in the northern part of Indus Basin, starts when the sun moves northward after March each year. This constitutes a major source of river flow. The Kailas range holds key to supply of water to two main river systems viz. the Indus that drains its water to the west and southwest, and the Brahamaputra, which flows east and then via Assam to the Bay of Bengal. It is interesting that both the rivers rise from Lake Mansarowar.
The glacier melt and snowmelt in the upper Indus catchment area are the source of 80% flow during the summer. There is only minor variation in the timing and volume of annual flow of snowmelt. 95 bcm or 84% of the total mean flow measured for the Indus at Kalabagh takes place between April and September, which is the kharif season4. The rise in flow volume due to snowmelt starts from early May and attains its height between the last week of June and first week of July, which is the time for the first flood flow. This is either accompanied or followed immediately by a higher glacial melt combined with monsoon rains in the catchment area starting from mid-July to August. The water level in the river starts falling from September and reaches its minimum between mid-January and mid-February, whereafter the upper reaches beyond Skardu run dry. The driest month for the Indus is February, with an average annual winter flow recorded for the 1956 to 1997 period being 17.95 bcm, while July has the highest seasonal inflow, the annual average summer flow being 112.2 bcm4.
The snowmelt, according to observations from the satellite imageries, starts from April each year. By mid-April there is substantial flow of over 30,000 cusecs and by the end of June 50% of the basin is free of snow. The remaining 50% of the snow cover keeps melting through the summer4. A recession starts in the snowmelt hydrographs towards the end of August until it hits the base flow towards the end of October. However, 18% of the snow covered area remains unaffected and does not see the light of the day4,5. Not much of recession in the glacier area is reported to have occurred since the meteorologists have been claiming a large amount of snowfall on the catchment area.
The monsoon system, which is the other constituent of the water budget, comprises the following sequences: (a) an eastward push of the warm current that starts from the eastern coast of Africa, (b) intense heating of the desert area extending from Balochistan, and Rajasthan to Central India in the east and from the desert areas of Kharan and Thar in Sindh in the south to the Potohar plateau in the north of Pakistan, resulting in heat waves from March to mid-June, with sizzling temperatures of 43oC to 48oC that would create low-pressure zone over the region with its focus on the Nokundi-Sibbi-Jacobabad axis, (c) the westward pull of moist air by the low pressure zone created by heat wave, (d) breaking of monsoon in early June at the southwest of the Indian Peninsula, (e) causing the monsoon winds to travel across the Indian Peninsula and over the Bay of Bengal, (f) picking up more moisture to the point of saturation and supersaturation and causing a series of storms by the simultaneous entry of moist air from the Bay of Bengal and from the Arabian Sea, (f) plenty of rainfall following the breaking of monsoon in Bangladesh, Nepal, the eastern and northern provinces of India, the snow covered mountainous region comprising the Siwaliks and outer Himalayas and the catchment areas of Indus and Brahamputra, which is by this time left with 50% snow cover, (g) intense and heavy precipitation over the area and the adjoining plains initiating the flood flow in July, (h) bifurcation of the system on reaching Central India with one of its branches entering Pakistan from the east and the other from its north and (i) diffusion of monsoon current18.
The warm current from East Africa and the winds accompanying it have sufficient driving force when they strike the southwest of the Indian Peninsula to move past its eastern coast in early June. The winds shed their moisture at this point but when they emerge at the western side of Bay of Bengal, they find the water warmer. They pick up more moisture from the Bay of Bengal, get saturated and supersaturated as they proceed landward to the northeast. The velocity of winds is reduced due to over-saturation and their rising in the form of towering rain clouds. The driving force henceforth is the temperature gradient i.e. the intensely heated, low-pressure zone extending from Central India to Pakistan and cold front of snow cover of the Himalayas. If the winds are weak the system fails to push moisture laden winds to the zone past central India into Pakistan and there is heavy rainfall in the eastern zone However, if the winds are strong they push the system westward to low pressure zone after shedding the water content over the Bay of Bengal. The winds lose most of the moisture during their travel from Bangladesh to Central India and the rainfalls in Pakistan are only of medium intensity.
There are two flood flows in the Indus river system; one due to the early rains in mid-July when the snowmelt contributes its share and the other in mid-August when it is mostly due to precipitation There is widespread flood and large areas are inundated when the catchment area is overfull due to increase in flow volume beyond the absorption and drainage capacity of the system. The rate of run off increases rapidly after each heavy downpour in the catchment area as was observed in 1973, 1988, 1992 and 1997 when there was heavy precipitation in the catchment areas of the rivers of the Indus system and large areas were inundated6. The volume of discharge during the summer season exceeds 10 to 20 times the winter flow.
Departure from Past Trend
Variations mostly due to macro-climatic changes have been recorded in the river flow due to snowmelt, in the magnitude and intensity of heat wave and in the occurrence of rains and floods during the last five years. The pattern of water flow due to snowmelt, which brings the first flood-flow in the Indus and Jhelum was not followed during the last two years. The Indus did not receive the flow volume as in the past to the extent that the Sukkur Barrage did not receive the flood flow for the first time in its history of 68 years7. Kabul was the only river, which supplied snowmelt and there was some water to be found in the upper reaches of Indus; downstream, it was running dry. Precipitation on the east of Lake Mansarowar, the catchment area for the Brahamputra on the heights of Tibet, was heavy and either the winds slackened so as not to reach the catchment area of the Indus on the west or there was not enough moisture in the clouds or snow cover left to contribute to the flow.
The inadequacy of snowmelt in the Indus system did not raise the inflow at Tarbela or Mangla till mid-April and even on April 17 this year it was a mere 20,100 cusecs at the former and 26,300 cusecs at the latter dam. The low flow continued till past the first week of May 20008. The observed low flow has been attributed to lower rainfall during the preceding five months. Since a similar situation was faced in 1994 and 1997, it is quite likely that the process of degradation of the ecosystem of glaciers was not critically examined although it had set in 1994 and has worsened in the mean time.
Much larger area in the north and south is reportedly being affected by heat wave and the heat zone is no longer limited to Balochistan, Sindh, Rajasthan and Central India but extends to Northern Areas of Pakistan and to Iran9. The focus of the heat zone extends along the Nokundi-Sibbi-Jacobabad axis to Mianwali. The departure from normal, as observed may not be unusual but is so persistent in recurrence as to suggest that either the established monsoon pattern is not being followed or modification of some sort, may be due to global warming as manifested by the intensity of heat wave, has taken place. During the few years prior to 1997, Sindh was receiving its first share of rains much earlier than Punjab and the mountainous north. In 1992, the year that was extraordinarily cold and wet, snowfall continued beyond the winter months, which delayed the snowmelt to the end of March. Intensive snow melting started the moment the solar heat became dominant over the mountains. The channels and rivulets were running full in early July and were causing floods in the Northern Areas much before the onset of monsoon. Extraordinarily high rainfalls and floods followed from early July.
The system of push from the Bay of Bengal and pull from Central India and Sindh-Balochistan on the west and northwest has been erratic in following its past pattern, again since the last five years. The bifurcation of the monsoon system from Central India at Jhansi into two branches, one going west to Sindh and the other going northwest to the Northern Areas of Pakistan, is not being observed. This provides support to the earlier statement that in proceeding towards the west, the system either loses the driving force to push rain clouds to the west or the pull of the low pressure zone over Sindh and Balochistan diffuses and offers no attraction. The failure of the monsoon has thus been occurring with regularity in the western segment of the cycle while heavy rains in its eastern segment are each time accompanied by devastating floods. Bangladesh was witness to the worst floods in history in 1998 and West Bengal in September 2000.
Precipitations and river flow have become erratic since the early 1990s. 1992 was erratic in being too wet and 1993 in being dry1. What followed thereafter was lower or delayed precipitation over the western segment of the monsoon cycle. The impact of the change became apparent immediately after the wet year of 1997 when the monsoon system failed to reach Pakistan as suggested by the below normal rainfall from July to August 20 of the year 1998. The rainfall thereafter was heavy and floods played havoc. There was below normal rainfall in 1999 while that received from the northwesterly system in the northern areas were slightly above normal in July 2000, but well below normal during August and very little in September.
Recent Observations
The inadequacy of snowmelt in the Indus system did not raise the inflow at Tarbela or Mangla till past the first week of May 20009. Condensation and heavy precipitation over the east of Mansarowar lake provided heavy flow to Brahamputra but not to Indus which is on the west of the lake. The water flow on September 4, 2000 was 84,500 cusecs at Guddu barrage, 60,973 cusecs at Sukkur barrage and 23,000 cusecs at Kotri barrage, as against 10 times the flow observed during a normal year10. At Sukkur barrage the flow volume had to be decreased by up to 1000 cusecs, which resulted in decrease in inflow and in the water level in four canals and in reduced flow downstream Kotri.
The scarcity of water is being reported from all over the country. None of its cities was prepared to meet the eventuality with respect to shortage of freshwater. Islamabad was first hit in its 33-year history by the worst water crisis in 1994. The critical situation has continued and 43% of the people in Rawalpindi were without water in summer of 2000. This city needs 47 MGD but was getting only 25 MGD during the January-April period11.
The drought conditions are prevailing all over Sindh including Karachi, Balochistan and Punjab. The worst affected areas in Sindh were those from the backward areas of Kacho and Kohistan in Dadu district, particularly Johi, Mehar, Khairpur Nathan Shah, Sehwan and Thano Bula Khan as well as the western areas of Kotri. Drought like conditions have hit Cholistan again where 200 ponds and tobas have dried up due to return of ht weather. The ponds were filled when rain fell in July and people who had migrated to greenbelt areas of Punjab for water and fodder returned home. Over 200 of the 350 ponds had dried up by end of September while a small quantity was left in the others due to no rainfall in August and an intense heat, which evaporated the water earlier than expected12.
There was heavy rainfall in Jammu and Kashmir and for three consecutive days in Sialkot13. This raised the water level of Chenab, Jammu and Tavi and nallahs Bhed, Dek and Aik which pass through congested areas of Sialkot city. The water flow in Chenab was 125,656 cusecs. Lahore recorded above normal rains of 329.9 mm at airport during July 2000 against the average of 217 mm and 199 and 105.8 mm in 1998 and 1999 respectively. The rain during the entire monsoon season of 1999 was 316.2 mm while the average is 427.1 mm. The heaviest ever rain in July was recorded in 1981 when 477.9 mm was recorded and in 1980 it was 470.6 mm while the lowest ever was in 1945 when it was a mere 1.3 mm. The remaining monsoon season received below normal rains. Southern region received only nominal rains of 10 to 30 mm and of a few hours duration13.
Islamabad and Rawalpindi received 22 mm rainfall on September 20 and 21 while scattered rains occurred in Upper Punjab, NWFP and Kashmir14. Severe floods following torrential downpour earlier on in the region hit West Bengal. Nearly 17 million people were affected and 6 million rendered homeless by heavy flows in the Ganges and 56 other rivers sweeping into Bangladesh. Large parts of West Bengal state and 11 western districts of Bangladesh were in a deluge that was the worst in 22 years. In Calcutta the high tide turned the Hoogly river into a swollen torrent on September 2815.
It rained 77.4 mm on the night of August 18 in the Indian State of Assam and the Brahamputra river swelled once again, subsequently submerging fresh areas. The floods, which began from July in India, Bangladesh and Bhutan had already taken the toll of several hundred lives and had rendered an estimated 4.5 million homeless. Kathmandu Valley records an average 100 days of monsoon season every year and the rainfall ranges from 1425 mm in the Biratnagar valley to 3000 mm in the Pokhran valley, with the Kathmandu valley getting over 1000 mm. Just as much as the above rainfall occurs during the rest of the year and the average total ranges from 2800 to 5800 mm16.
The monsoon system started receding after the above heavy downpour, which occurred all over western India including Nepal. The monsoon trough line marking the excessive concentration of rain making clouds started shifting gradually in the year 2000 towards Bihar in the eastern-central province of India. In the first week of August the trough line was centred on the Terai or the districts on the slopes of the Himalayas in Nepal and there was record heavy rainfall of 98.6 mm in the Valley, on August 8, 2000, up from 92.8 mm in 1973. It was around the same time in August 2000 that huge landslides caved in on the Krishnabhir section of the Prithvi Highway. There was above normal rainfall during June when there was heavy downpour but July rains were below normal while August rains were above normal16.
Analysis and Explanations
Pakistan, incidentally is not isolated in the crisis of its water budget. Scarcity of water is looming large all over the arid regions of the earth. The crisis in the monsoon region is in the interruptions of the cycles of wetness and dryness and that has become prominent during the last five years. It is this crisis that is seeking answers on whether it is due to changes in climate resulting from the cyclic events that govern the climate, and if so, whether it is of permanent nature, or it is due to the ecosystem misbalance. Observations on the pattern of flow due to snowmelt, intensity of heat wave, precipitation data and occurrence and severity of floods in the region do suggest that some alteration has occurred in the system, in general and at the tail end of the monsoon cycle in particular. The monsoon system has, in not following its previous pattern, resulted in water scarcity and serious drought conditions over extensive areas, which are continuously expanding.
The failure of the monsoon system could be due to interventions in the cyclic processes that govern the water balance on the earth. Explanations can just as well be provided in terms of cycles of wetness and dryness as done by Shnitnikov’s analysis17, and in terms of El Nino and La Nina factors that are a local manifestation of global events taking due account of the persistent domination of these events19.
Shnitnikov analysis of the variation in ground and surface water, glaciation and changes in plant communities shows the existence of a general law of terrestrial humidity cycle, which repeats every 1800 to 2000 years. The results are confirmed by the cycles of snow cover and glaciation. The present erratic variations attributed to climate change may very well be following the terrestrial cycle by which the earth may be passing through a transitory period from highly humid to a dry phase. The droughts are becoming too frequent because continents are losing their share of land while oceans are gaining in volume of water and expanding in area. The above conclusions are based on the observations over the last century, which show that 430 cubic km of water are being lost annually from the land and the level of seawater is rising at a rate of 1.2 mm annually17.
Periods of greater and lower humidity affect vast areas of the earth but at no time do they involve the whole of the earth. The period of high humidity in one part is accompanied by reduced humidity elsewhere. The period of run-off in the drainage basins of the major rivers and the boundary of such areas is fairly constant and seems to follow a cycle extending over a certain number of years. For example, between 1926 and 1930 the run-off was abundant in Europe and North America, but it was reduced in the rest of the Northern Hemisphere. For the 1931 to 1940 period there was reversal; the area excluding Europe and North America received higher run-off. The peak and low discharges in the run-off occur at different times in the different well defined but large zones of the earth17.
Cyclic variations in stream flow of rivers, were analyzed by Kalinin who suggested that cycles that recur most frequently are with periods of 2 to 3, 5 to 7, 11 to 13 and 22 to 28 years. The 11 to 13 year cycles are regarded normally as being governed by solar activity17. Cycles of dryness and wetness have been well recorded for Karachi and they are adequately explained by Shnitnikov analysis. Long dry spells are not common in Karachi; the maximum period ranges from 7 to 9 months over a period of at the most one year. However, the drying up of Hub dam and reduced water flow in the Indus are indications that perhaps the persistent domination of La Nina factor has induced a climate change that has disrupted the cyclic process. The cycle of dry spells repeats in 47 to 53 years, the first one to be noted was from October 1857 to June 1858, the second from April to December 1904. This cycle repeated as expected in 1951 when there was low rainfall. The last ones that occurred were in 1987 followed by that in 1993 and now in 1999 and 2000.
The gap between heavy rain years in Karachi varies from 4 to 11 years with the longest one extending over 50 years. Records are available to suggest that there is the periodicity of 50 years e.g. 1863 (347 mm), 1913 (341 mm), and 1961 (610 mm); for 1866 (343 mm), 1916 (555 mm), and 1967 (713 mm); 1878 (605 mm), 1926 (509), and 1977 (207), and for 1894 (577 mm), 1944 (745 mm), and 1994 (450 mm). S.N. Naqvi had, in his analysis of the meteorological data, suggested the existence of a short cycle of 3 to 5 years, a medium cycle of 10 to 13 years, a Bruckner's cycle of 18 to 23 years and a long cycle of 50 years. The data indicate large fluctuations from year to year but there is genuine orderliness among them over a decade and still better correlations over a 30 year period18.
The available records apparently suggest that the natural process of compensating the deficit of one year with excess in the following year has been adequately maintaining the water balance in Karachi. The present crisis of shortage of water could therefore be considered as part of the natural system. The cycle of precipitation, if the data have any meaning, suggests that since the deficiencies of the past years are compensated, the two years following 1995 and 1996 should have been deficit years and that the next dry spell should have occurred in 199918. Incidentally this happens to be the case. Accordingly 2002 should be a very rainy year. The critical situation, which has precipitated in the form of drought, thus appears to be part of the natural repetitive cycles.
The change in the monsoon pattern had been felt in the early 1990s but the onset of a dry cycle became apparent in 1998 when the below normal rainfall from July to August 20 was followed by heavy rainfall and floods in the last ten days of the month. The abnormal rains and the prediction of above normal rains in Pakistan for the 1998 monsoon season was reviewed and it was observed that the opposite of the El Nino effect, the La Nina factor had not been taken into consideration by the Pakistan Meteorological Department. The El Nino factor, which causes warming of the waters was active from May 1997 to May 1998 and had, because of its high activity on the Eastern Pacific viz. the coast of Ecuador and Peru, caused record heavy rainfall in 1997 in Pakistan. After the cessation of its activity, the cooling of the ocean and dry weather due to the La Nina factor is routinely followed. It became active on Eastern Pacific in May 1998 and is responsible for the dry weather that is being witnessed in Pakistan from that time onwards.
Climate, ocean current, wind and vegetation being critical components of the global system, disturbance in one part of the sequence or succession of events inevitably impacts the other part and quite frequently at unexpected places, the El Nino effect being the result of such a disturbance. The unusually high frequency of the inception of El Nino weather effect during the past few years has possibly been triggered by the rise in ocean water temperatures in the eastern Pacific, and it is accompanied by drought in Australia, western India, Indonesia, Pakistan, Iran and Africa and for flooding in South America, eastern India and Bangladesh19.
The La Nina factor produces the rain generating cyclonic circulations in the Bay of Bengal. The development of low pressure over the Bay of Bengal in mid-1998 was too weak and too localized to respond to the low pressure zone in the west or to cause rains in Pakistan. The cooling effect of the La Nina factor dampened the warming effect of the high temperatures that sizzled many parts of Central Pakistan. The La Nina effect related to cyclonic circulations is caused by warm sea surface, and deep portion layer, low-level rotation and mid-level moisture in the air. It surfaced up in May 1998 and not in March 1998 when the above normal rains had been forecast. The below normal rainfall in 1999 was also attributed to the La Nina effect.
It appears that the rains received from the northwesterly system in the northern areas in July, well below normal during August and September 2000 and very little in the southern region during the entire period are again to be attributed to the La Nina effect. The low pressure over the Bay of Bengal was again too weak to allow the system to travel past West Bengal and as such there was heavy rainfall, the like of which was witnessed 22 years back. The precipitation took away the critical amount of moisture that can cause rains in the region over which the system was to travel. When it ultimately reached Central India and Pakistan, much of the moisture had been diffused into the aridity prevailing there and there was very little rain capacity left in it, and hence the scattered rains in Islamabad.
The above analysis only partly explains as to why the monsoon system is not following its past pattern for the past five years at the western end of the cycle, although it does operate as usual and brings plenty of rainfall in Bangladesh, and the eastern and northern provinces of India. It also does not explain why the above normal rains in Pakistan and Nepal in July are each time followed by well below normal during August and very little in September. In both countries the system apparently started receding in mid-August after the usual heavy rains at the start of the season.
The crisis of below normal rainfall all over, drought conditions prevailing in the southern region for the past five years, inadequate snowmelt and the consequent lack of flood-flow in the Indus and Jhelum during the last few years as well as in 1994 and 1997 may suggest an ecosystem misbalance in the glacier area of concern to the Indus system. It could, if it is real, be related to the impact of global warming, which is being increasingly reported during recent years to be responsible for shrinkage of glaciers, recession of the snow cover on the coastline of Greenland, and for the finding that the ice at the North Pole was in molten condition in June this year. However, when a giant iceberg of the size of Jamaica, close to being record size with a length of 295 km and width of 37 km, was broken free from Antarctic’s Ross Ice Shelf, in March this year, no alarm bell rang. It was considered a normal phenomenon since the ice sheet has to maintain a balance20. The chip-off may then be related to cycles of wetness and dryness noted and explained by Shnitnikov analysis.
Conclusion
The unusually high frequency of the damaging El Nino weather patterns in recent years, triggered by the rise in ocean water temperatures in the eastern Pacific, has been held responsible for the drought in Australia, India, Indonesia, Pakistan, Iran and Africa and for the flooding in South America. The abnormal events that may have led to the persistence of La Nina factor and recurrence of drought are taking place at the same time when Pakistan is facing the low flow in its rivers. The Shnitnikov and Kalinin analysis do suggest that the observed visible disturbances in the succession of events regulating the water balance in Pakistan may be related to the cyclic events. This analysis seems to be valid in the case of abnormal rainfall in Karachi and in the onset of drought conditions towards the end of the millenium18.
The incidence of the El Nino event followed by the La Nina factor also provide suitable elucidation but the La Nina factor is expected not to be persistent. These odd events and the resultant climate change may as well be attributed to expansion of the heat zone from the Kharan-Thar-Rajasthan to include Iranian Kharan in the west and the Northern Areas of Pakistan in the north. This possibly restrains the monsoon winds to flow past central India and diverts it northward. This may explain as to why Pakistan receives scanty rainfall while the eastern segment of the monsoon cycle and the catchment area of Brahamputra and not Indus receive the maximum precipitation.
References
1. Economic Survey 1999-2000, Government of Pakistan, Finance Division, Economic Advisor’s Wing, Islamabad, 2. The Pakistan National Conservation Strategy, Environment & Urban Affairs Division, GoP, and IUCN, 3. Balochistan Conservation Strategy, IUCN, 2000,
Karachi harbour, Pakistan Journal of Marine Sciences, 4(2), 159-74, 1995, 6. H.T. Sorley (1964) The Gazetteer of West Pakistan: The Former Province of Sind, Government of West Pakistan, Lahore, pp-11, 7. Dawn October 20,2000, 8. Dawn daily, Karachi, April 18 and May10,2000, 9. Dawn daily, Karachi, May 25,2000, 10. Dawn daily, Karachi, September 6,2000, 11. Dawn daily, Karachi, August 3,2000, 12. Dawn daily, Karachi, September 25, 2000, 13. Dawn daily, Karachi, July 24, 14. Dawn daily, Karachi, Sept 24, 15. Dawn daily, Karachi, September 29, 2000, 16. Kathmandu Post, August 19, 2000,
Ecology of Man: An Ecosystem Approach, ed. R. L. Smith, Harper & Row Publishers, New York, 1972,
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