Pakistan is suffering from a severe drought for the last three years. A regional workshop on water management was held recently at Lahore which was organised by the Pakistan Council of Research in Water Resources (PCRWR), in collaboration with the South Asia Association for Regional Cooperation (Saarc) and it was attended by experts from various countries. Five of the experts from Pakistan spoke on various aspects of water management.

The major emphasis of these experts was on defining drought, its forecasting and suggesting water management strategies mainly of surface and groundwater for mitigation of drought, while the vital subject of rain water harvesting technology as followed in many countries was hardly referred. Therefore, the writer has taken up this issue in the national interest.

Water harvesting is the process of collecting and storing water from areas that have increased run-off of rainfall and snow melt. Once rainwater run-off has been harvested from slopes, it can be used for crop production. The combination is called as run-off farming. It is recognized that harvested water is a scarce commodity and has rightly been termed as liquid gold.

Collecting surface run-off during periods of excess rainfall and using it during subsequent dry periods in rainy season or early in dry season, markedly decreases risk involved in rain-fed farming system. A wide-range of modern technologies have been developed in the USA, China, Australia, Mexico, Israel, Syria, Turkey,India, etc; for rain water collection and its utilization for crop production, range improvement, livestock and human consumption in otherwise non-productive areas.

Potentials: Although rain does not fall frequently, especially in arid and sub-arid regions of Pakistan, yet it brings considerable amount of water when it falls: 10mm of rain equals 100,000 litres of water per hectare. Harvesting this water can provide water for regions where other sources are too distant and costly. Rain water can be harvested in areas receiving 50-80mm of average rain which seems to be the lowest limit. Fortunately, in Pakistan the annual rainfall varies from less than 100mm to over 1000mm with an average of 400mm suggesting that there is good potential of water harvesting and run-off agriculture.

The estimated average annual rainfall in the country is 180 million acre feet (maf) and 50 per cent of which is lost as run-off. Even if the run-off is taken at 20 per cent, the average annual run-off loss of water comes to 36 maf which is a huge loss which the nation can ill afford. The existing conventional water harvesting practices in the arid and semi-arid regions hardly collect 20 to 30 per cent of the precipitation while more elaborate technology may permit to collect up to 90 per cent of it thus significantly increasing the yields of our rain-fed crops.

Keeping in view the increasing population and declining water resource base, policy makers and planners should give serious consideration to modern water harvesting and run-off farming system in Pakistan. The various water harvesting techniques which have a good potential of conservation of water and its subsequent use for increasing yields of rain-fed crops, increasing availability of water for human and livestock consumption are given as under:

Techniques: These techniques have two components; the run-off area and the run-on area. Run-off may be harvested from rooftops of residential and commercial buildings and other ground surfaces as well as intermittent, semi-perennial and perennial streams. Run-on area is where water is stored until needed which may be in the form of small cisterns, tanks of steel, concrete, fibreglass, earthen ponds or artificial recharge of groundwater. Some of the practicable rain water harvesting techniques that can be adopted in Pakistan are discussed below.

Land alteration: A simple water harvesting is to clear some of the vegetation upland and collect the runoff resulting in natural drainage. Smoothing and compacting the runoff area will increase the runoff on to the run-on area. Another simple method in low rainfall areas is collection and concentration of runoff water in the cropped area from the modified soil catchment area.

For example, at Avadat in Negev Desert in Israel, each hectare cultivated land receives runoff from 20 hectares of slopped land made impervious by the use of sealants as well as direct rainfall. Thus, the cultivated area receives water roughly equal to rain fall of 300-500mm from actual rainfall of 100mm.

Under this runoff agriculture fair yields of crops are being obtained. In Arizona, in an area receiving 250mm of annual rainfall, this water harvesting technology enabled to achieve rain-fed crop yields comparable to those from conventional irrigated crops. Similarly 50 mm of additional water harvested in addition to the incidental rainfall enabled to increase the yields of rain-fed maize, sorghum and pearl millet by 95, 97 and 107 per cent, respectively.

In India where nearly 70 per cent of their cultivated area is rain-fed and contributes nearly 50 per cent of their total food grain production. These land alteration methods have good potential of increasing yield in arid regions of Pakistan, especially in Balochistan, where initial studies enabled to take good crop yields of wheat, barley, lentil and vetch.

Terraces: Terracing is a method most commonly used to control water erosion and to intercept rain water on agricultural and wastelands by constructing broad channels across the slope of rolling land. Contouring of cultivated land is always combined with terracing. The function of terracing is to decrease the length of hillside slope thereby reducing sheet and rill erosion, preventing the formation of gullies and increasing water infiltration in the soil by retaining runoff and provide a built in safety factor for rains of high intensity.

If terraces are built with a wide channel having gradual front and back slope than the entire surface may be farmed. However, terraces are not recommended on slopes over 20 per cent. In some regions slopes 10 to 12 per cent are considered maximum. Different types of terracing (stone, broad based and bench type) can be constructed according to slope, soil type, crops to be grown and other topographical parameters. They can be designed for the control of runoff in high rainfall areas and for the conservation of water in low runoff areas.

Contour farming: In this method runoff is reduced by trapping water in furrows or stone bunds, thereby increasing retention and infiltration of water into the soil. Well defined contour furrows are recommended in all sloping lands where water is limiting. In some areas where water deficit is a major obstacle for agricultural development, stone bunds in conjunction with contour furrows, can be effectively used to trap water and maintain soil furrows.

The terrace and contour farming has a good potential in mountainous, hilly and upland areas of Pakistan. Micro-catchment farming: Of all runoff farming systems micro-catchment provides the highest percentage per unit catchment area. A plant can grow in a region with too little rainfall for its survival if a rain water catchment is built around it. This practice is called micro-catchment. The basin stores runoff from micro-catchments. However, the size of basin is designed according to the expected yield of water, topography and spacing between the plants.

Grape vines, pomegranate and other fruits are grown in Negev Desert receiving only 100mm of annual rainfall suggesting that this technology should be tried initially in our sandy deserts receiving over 100mm of rainfall. Again, olive micro-catchment is practised in Tunisia suggesting potential of similar olive farming in Pothwar plateau, Parachinar and Quillah Sufaid areas of Pakistan.

Inter-dunal water harvesting: In our sandy deserts areas receiving 100 to 250mm rainfall in Cholistan, Thal Deserts, water may be harvested by using compacted and shaped slopes of sand dunes as natural catchments and using the inter-dunal depressions or basins as cultivated areas. The catchment to cultivated area ratio should be 50:50 or may be designed according to the situation. The compacted catchment treated with a thin pond sediment or other sealant materials and slope of 3 to 6 per cent will increase runoff efficiency. Pearl milet, sorghum, guar, sesame or fruit and forest trees and range species best adopted to desert environments should be tried. It will also be desirable to set apart a portion of land for harvesting rain water in cemented pond or tank and using it as life saving irrigation to crops during prolonged droughts. India has already successfully adopted this sand dune culture in their adjoining Rajisthan Desert.

Hill torrent water harvesting: There are 14 hill torrent areas with an average water conservation potential of 18.6MAF of water at 1204 conservation sites. Of which 60-70 per cent can be used for the development of 6.35 million hectares of culturable wasteland lying in these hilly areas. Presently the major part of these flows go waste. The potential areas for the development of hill torrent agriculture are Hazara, Bannu, DIKhan, DG Khan, Kachi Basin, Kirther Range, Karachi area, Sehwan and Petaro area hill torrents. The previous conservation structures mostly failed as they were not based on sound engineering principles. This mistake may not be repeated while building new torrent water conservation structures.

Lift Irrigation: Surface irrigation may not be feasible everywhere. On high mountains and hilly areas in the country rain water flows from mountain and hill slopes to deep streams and rivers. This water can be harvested for irrigation of areas along the high banks of these streams and rivers by lift irrigation by water power driven water turbines and hydra-ramp pumps. This mountain technology developed by China is very successful for crop production on mountain and hilly areas. A water turbine may lift water to over 30 meter height at 60-70 litre per second besides producing 5 kw of hydro power. These turbines do not need diesel or electricity for their operation. In upland rainfall areas where such streams are non-perennial, intermittent or ephemeral, there water may be lifted and stored in ponds and tanks during rainy or short flood season and used as supplemental irrigation during the closing or post monsoon season for increasing the yields of rainfed crops. This technology has already spread in the mountain and hilly areas of several countries in South East Asia.

Harvesting of glaciers: Due to severe drought in Northern Areas, the Agha Khan Rural Support Programme engineers successfully tested harvesting of patches of ice glaciers and transporting them to a few drought stricken villages to meet their domestic and agricultural requirements from the melted water of these glaciers. This technique of harvesting natural glaciers needs careful evaluation of its impact on environment and natural supply of water to the Indus River system and its tributaries in the long run.

Roof-top water harvesting: Runoff is being harvested from the roof tops of residential, commercial and industrial buildings in many countries of the world to meet the declining groundwater requirements for domestic and industrial purposes as rain water is the only fresh water alternative. The system comprises of roof top rainwater collection and recycling device. The system has been made mandatory in many Indian cities to reduce ground water exploitation. Even the annual requirements of Indian President’s Palace are met from its roof top water harvesting and recycling it. The Indian government had earmarked Rs45 crores in its 9th plan for rain water harvesting and has given directives to the state and municipal bodies to undertake roof top rainwater harvesting and its recycling for domestic use and its recharge to groundwater mandatory for every dwelling unit by amending city bye-laws.

On the other hand our big cities like Rawalpindi, Islamabad, Karachi and Lahore are facing serious water shortages but there is no plan of utilizing fresh roof top rainwater harvesting. Instead water from Khanpur Dam is being diverted to meet the domestic water requirements of the twin cities of Islamabad and Rawalpindi which could be saved for agricultural purposes. Nevertheless, the roof top water harvesting technology is now expanding in USA, Cyprus, and many other countries in the world to meet their domestic, agricultural, lawn, fish pond requirements and groundwater recharge.

Drought episodes have increased over the last two decades. According to the World. Watch Institute, 1.1 billion people lack access even to potable water. Again, nearly 1.4 billion of the world’s population including that of Pakistan lives in regions that would face severe shortages of water in the first quarter of the new millennium according to an international research study.

Thus keeping in view the impending shortage of water the policy makers should also give top priority to rain water harvesting in its water development projects. A rainwater harvesting authority be established to make rainwater and roof top water harvesting mandatory to reduce groundwater exploitation and meet the increasing water needs of the urban and rural communities in the country.