Of all the natural disasters, drought whether Meteorological, Hydrological or Agricultural has the greatest potential impact as compared to other disasters like floods, tropical storms etc. as the latter are mostly of short duration and geographically limited and droughts, by contrast, affect large geographic areas often covering the whole of the countries or even parts of continents. Droughts may last for months and in some cases several years.

DEFINITION OF DROUGHT

Drought is commonly associated with periods of reduced precipitation of sufficient duration to cause insufficient water resources. The loss of these water resources, in turn, disrupts natural ecosystem and human activities. However conditions that initiate drought in one region of the globe may go unnoticed in another. For example a few consecutive months without precipitation over Cholistan, Thar and Nokkundi deserts constitute a drought whereas over other regions like the plains of Punjab where surface water making part of the perennial flows and ground water are available may not suffer from drought under similar conditions. There is as such no precise definition of the word “Drought” that can be universally applied to all the regions.

However the definition given in the Meteorological Glossary, printed and published by Her Magesty’s stationary office, London in 1972 is produced below: -

“Dryness due to lack of Rainfall. Drought and partial drought were defined in British Rainfall 1887 in order to obtain comparable statistical information for inclusion in each annual volume of this publication. “An absolute drought was a period of at least 15 consecutive days to none of which was credited 0.2mm, or 0.01 inch, or more of rainfall.” A “partial drought” was a period of at least 29 consecutive days the mean daily rainfall of which did not exceed 0.2 mm, or 0.01 inch. A “dry spell” was first defined and used in British Rainfall 1919, a dry spell being a period of at leat 15 consecutive days to none of which was credited 1.0 mm, 0.04 in, or more of rainfall.”

TYPES OF DROUGHTS

There are three types of droughts namely Meteorological, hydrological and Agricultural. The first two types describe physical events where as the third describes the particular impact of the first two types on an area of human activity. The three types are briefly described as under:-

Meteorological Drought:

Meteorological drought involves a reduction in rainfall over a region for a specified period (day, month, season, and year) below a specified amount, usually defined as some proportion (percentage) of the long term average for the specified time period. Its definition involves only the precipitation statistics.

Hydrological Drought:-

This involves a reduction in water resources (stream flows, reservoir levels, ground water, underground aquifers etc) below a specified level for a given period of time. Hydrological drought occurs when a lengthy meteorological drought causes a sharp decline Hydrological drought occurs when a lengthy meteorological drought causes a sharp decline in the levels of ground water, rivers and lakes. For example, lack of winter snowfall over the mountains of northern areas and failure of monsoon rains during the monsoon period has a serious impact on water availability for the country in the subsequent months.

Agricultural Drought:

This emerges due to the impact of Meteorological and Hydrological droughts on a particular area of human activity. In order to achieve the optimum growth, crops have particular temperature, moisture and nutrient requirements during their growth cycle. If the moisture availability in particular falls below the optimum amount during the growth cycle, the crop growth will be impaired and yields reduced.

CAUSES OF DROUGHT

Drought conditions appear over any of the vulnerable zone when the rain producing systems fail in succession. Winter rainfall generally fails when the tracks of western Distrubances which move on to our area from the west, remain at a latitude of 35° N or higher. Under such a situation, no secondary western disturbances form below 30°N and consequently Sindh province and parts of Balochistan can completely go dry. This situation has been found to occur quite often. The situation get aggravated if the subsequent months of April and May also go completely dry and temperatures become very high which is a normal feature of these months. Evapotranspiration tremendously increases and results in perpetual drought. During the summer months June to September, if a monsoon low or monsoon depression which forms over Arabian Sea or over Bay of Bengal fails to reach our areas, the monsoon rains are very scanty and that too in the northern parts of the country which include northern divisions of Punjab, parts of NWFP & northern areas. Infact the rains over these areas occur due to the incursion of South West winds from the Arabian Sea when these are accentuated due to the passing western disturbances. Conditions further aggravate if the failure of summer rains is further supplemented by no rains during October & November as was the case this year in Cholistan region from where tribes and nomads had to shift to other places and Government had to take emergency measures during the drought period.

El-Nino and La-Nina phenomena are the recent discoveries in the science of Meteorology. These are abnormal weather phenomena. Whenever they appear, they change the weather patterns over the globe. For instance, the strongest El-Nino on record occurred in 1982-1983. The monsoons in 1983 failed badly. Again 1997-98 was the strongest El-Nino year on record and was comparable to the one in 1982-83. The year 1998 also recorded no significant flood events like that of the year 1983. Such a striking resemblance is something thought provoking and needs to be further examined. Similarly La-Nina at times becomes a source of abnormal weather and may bring drought conditions.

AREAS VULNERABLE TO DROUGHT IN PAKISTAN

In order to mark the areas vulnerable to drought, a study of the rainfall activity over the country in different seasons and then on the basis of that marking of the areas remaining dry for more than 50% of the time, is required. There are two marked rainfall periods namely winter (December to March) and summer monsoons (June to September). If the seasons go dry, they are apt to bring drought conditions. “April to May” and “October to November” are the transition periods. Very little rainfall occurs in Sindh, Southern Punjab and Balochistan during these periods.

RAINFALL PATTERN OVER PAKISTAN

Pakistan is a country, which comprises of the arid, semiarid & hyper arid regions and a belt of humid climate along the foothills of Himalayas. In view of the drastic changes in climate, rainfall pattern and amount of precipitation falling on different regions vary considerably. Pakistan which has the mighty Indus River System flowing with its tributaries, has a great amount of variability in terms of when and where the water is available. Indus is more a snow fed river than its other tributaries viz Jhelum, Chenab, Ravi & Sutlej rivers. Most of the annual flow may come a flood following snowmelt or heavy rains and unless captured by reservoirs, the water flows to the seas, at times, causing seasonal flooding. Later in the year, the same or other areas may suffer droughts.

1. RAINFALL PATTERN DURING WINTER SEASON

Western disturbances or the low pressure systems which have their origin in the Mediterranean Sea or Atlantic Ocean travel eastwards in higher latitudes within 30° to 60° N. These systems have frontal properties. However a complete frontal system seldom exists in Pakistan. Whenever these disturbances induce secondaries in the lower latitudes (25-30° N), these pull moisture from the Arabian Sea and produce reasonably good amount of rainfall over the northern parts of the country and comparatively less over southern Punjab and Balochistan parts of the Central, Southern and Eastern Sindh which do not fall within the domain of winter rains, remain more than 50% of the time completely dry and as such is termed as a zone vulnerable to drought during this season. A comparative statement of weighted precipitation (1961-90) over different provinces reflect the drastically low precipitation over Sindh which on the average is 4.9, 5.7 & 16.1 times less than the precipitation over the provinces of Balochistan, NWFP & Punjab respectively.

Table-1

COMPARATIVE STATEMENT OF WEIGHTED PRECIPITATION OVER DIFFERENT PROVINCES DURING WINTER PERIOD (DEC. TO MAR.).

(1961-90)

PERIOD	NWFP	PUNJAB	BALOCHISTAN	SINDH
Dec to Mar (Winter) No. of times higher than Sindh	228.8 16.1	81.1 5.7	69.3 4.9	14.2 1

Precipitation over Sindh province as compared to other provinces is drastically less in winter months.

The aridity increases towards the Southeastern Sindh. Unfortunately, the transition zone of April to May follows the winter season when the temperatures increase rapidly and enhance the drought conditions because of high evapotranspiration & very less rains. Sindh is under the influence of the Indus River and mostly areas in the province are canal irrigated. The depth of ground water (Irrigated Agriculture of Pakistan, Dr. Nazir Ahmad) available in the province saves it to a greater extent from the Meteorological drought. It is observed that the depth of ground water along the river within a reach of 5 to 20 miles always remained at a high level.

2. RAINFALL PATTERN DURING SUMMER SEASON

The rainfall in summer (June to September) either occurs due to the monsoon systems coming from the Arabian Sea called SW monsoon systems or due to the intense lows called monsoon depressions coming from the Bay of Bangal which originate in the China Sea or adjoining region of he pacific ocean. The South western parts of Balochistan & some central portions of Balochistan and a portion of North West Sindh around Jacobabad, Sukkur, Rohri & Larkana which do not fall within the monsoon rains, remain more that 50% of the time dry and are termed vulnerable to drought. The conditions get more severe towards SW Balochistan around Dalbandin, Nokundi, Zahidan & Jiwani. Comparison of rainfall over the drought vulnerable parts with that of other provinces in summer (June to Sep.) is given in Table 2.

Table-2

COMPARATIVE STATEMENT OF WEIGHTED PRECIPITATION OVER DIFFERENT PROVINCES DURING SUMMER PERIOD (JUN. TO SEP.)

(1961-90)

PUNJAB	NWFP	BALOCHISTAN	SINDH	AVERAGE RAINFALL OVER THE VULNERABLE AREAS OF BALOCHISTAN*
260.3 12.2	252.9 11.8	64.2 3.0	137.5 6.4	21.4 1

* The area include Nokundi, dalbandin, panjgur, Jiwani, Pasni, Ormara, Kalat, & Quetta. (Mean normal precipitation over these areas is given).

3. RAINFALL PATTERN DURING APRIL & MAY

Western Disturbances while moving across the higher latitudes above 30°N, shed out sufficient moisture in northern areas. Beyond 30°N in south, the rainfall drastically drops and the whole of Sindh, part of Northeast Balochistan, around Sibi & Kalat, coastal areas of Balochistan and western limb of Balochistan around Nokundi become vulnerable to drought. During these months, temperatures are quite high. Maximum temperature often ranges from 105°F to 112°F. Jacobabad is one of the hottest places of the world which attained the highest temperature of 127.4° F (53°C) on 12^th June, 1919 and temperatures usually remain around 50°C during these months which can aggravate the situation by excessive evapotranspiration. Here again province of Sindh is not that vunerable to drought as sufficient ground water availability can reduce the impact of meteorological drought in some areas where ground water can be exploited easily. However the areas in Balochistan are always at risk with regard to the drought conditions as even during the summer months (June-September), these areas remain apt to the drought conditions. Comparison of rainfall in different provinces during these months (April to May) is given in Table 3.

Table 3.

COMPATATIVE SATATEMENT OF WEIGHTED PRECIPITATION OVER DIFFERENT PROVINCES DURING APRIL & MAY.

(1961-90)

NWFP	PUNJAB	BALOCHISTAN	SINDH
36.5 6.6	106.5 19.4	20.1 3.7	5.5 1

The rainfall over Sindh is 4, 7 & 19 times less as compared to Balochistan, Punjab & NWFP. The drought vulnerable areas in Balochistan receive similer type of precipitation as in Sindh. If the summer rains too fail, the conditions may get aggravated. However the drought conditions in this region get considerably subsided as groung water availability is there in the province.

4. RAINFALL PATTERN DURING OCTOBER & NOVEMBER

Comparitively higher rainfall received in the northern half of Pakistan whereas it declines drastically in Southern Punjab, Sindh & Balochistan causing these areas vulnerable to drought conditions. Similer conditions persist in Sindh province even in winter months from December to March. A Comparative statement of precipitation over different provinces during these months (Oct-Nov) is given in Table 4.

Table 4.

COMPARATIVE STATEMENT OF WEIGHTED PRECIPITATION OVER DIFFERENT PROVINCES DURING OCTOBER TO NOVEMBER

(1961-90)

NWFP	PUNJAB	BALOCHISTAN	SINDH
37.7 8.6	11.3 2.6	4.8 1.1	4.4 1.0

RAINFALL DURING LAST THREE YEARS (1998-2001)

Rainfall affects the lives and economies of a majority of the Earth's population. Rain systems, such as hurricanes, typhoons, monsoons, and fronts are crucial to sustaining the livelihood of many countries. Excess rainfall can cause flood, property and crop damages. A deficiency causes drought and crop failure

Rainfall plays another important role besides sustaining our crops and ourselves. It is the major source of energy for driving the circulation of the atmosphere since changes in the phase of water from liquid to vapor and back to liquid permit the storage of latent heat. Latent heat plays a major role in atmosphere circulation, making tropical rainfall an important determinant of circulation and short-term climate changes.

The rainfall during the last three years (1998 to 2000) over Pakistan was occurred in great deficiency. Following chart shows that during these years the rainfall were over all significantly below normal and largely below normal in some parts of the country In Sindh and Balochistan provines some of the areas got no rainfall or very little rainfall. This deficiency of rainfall has caused severe drought conditions, crop failure, and shortage of water in rivers & reservoirs and depletion of under ground water.

DROUGHT HIT AREAS.

Almost all the semi-arid and arid areas of Pakistan experienced current drought with varied intensity. The severity of drought reached its climax in low rainfall zones including most of Balochistan, southern parts of Sindh and southeastern parts of Punjab as shown in the figure.

The annual total rainfall ranges between 35mm and 110mm whereas the annual loss of moisture through evapotranspiration reaches 2000mm. The climate of these areas ranges from arid to hyper-arid where ratio of precipitation to evapotranspiration vary from only 1% to 10%. The mean annual rainfall fails to meet 75% to 90% of mean annual evaporation in these areas. In arid zone crop production is uneconomical under rain fed conditions. The plains located in the south of 33° N latitude are arid in nature, the agricultural production is not possible unless supplementary irrigation is made available. Luckily the world’s famous canal irrigation system exists to irrigate most of the arid plains of Punjab and Sindh. At present due to continued low precipitation over the river catchment areas. The available water for irrigation purpose is also under stress & sufficient water supply is not possible to meet the crop needs & civic like resulting hydrological drought conditions over the country.

DROUGHT PREDICTION

No known method exists to reliably predict the occurrence, continuation, cessation or recurrence of drought, although experimental forecasts are being issued in some parts of the world and accuracy does not contain encouraging results. Active research programmes are under way to understand the causes of droughts and hence lead to better predictions, but scientific problem is difficult so it may take some years to obtain a solution. However, analysis of climatological data can help to prepare probability assessments of the occurrence, cessation or recurrence of droughts, thus helping farmers and planners.

Remote sensing technology is widely being used to monitor impacts of drought on agriculture, water sector and related fields. Pakistan Meteorological Department in collaboration with international agencies had been monitoring the progress of current drought since its emergence during the persistence of El-Nino event of 1997-98. Drought advisories were regularly issued with specific emphasis on the current status of surface and ground water resources along with the outlook for the next month. SPOT image of 2^nd decade of May 2001 depicts large decrease of vegetation over northern half of country due to the failure of winter rains as compared with 1998.

HISTORY OF DROUGHT IN PAKISTAN

Droughts have been occurring in Southern Asia in the past too. Areas now comprising of Pakistan experienced several drought years 1899, 1920, 1935 etc. NWFP areas in 1902 and 1951 whereas Sindh experienced its worst droughts in the year 1871, 1881, 1899, 1931 etc.