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Geography and population

The Philippines is a tropical country consisting of more than 7 000 islands. It is one of the largest island groups in the world covering a total area of 300 000 km2, 92 percent of which is accounted for by the 11 largest islands. The archipelago is bounded by the South China Sea in the west, by the Philippines Sea (Pacific Ocean) in the east, by the Sulu Sea and Celebes Sea in the south and by the Bashi Channel in the north. Its northernmost islands are approximately 240 km south of the island of Taiwan, and the southernmost islands lie 24 km off the coast of Borneo (Malaysia). Of the 7 000 islands, only 3 144 are named. There are also thousands of small islets grouped with the larger islands. The Philippines is divided into three major island groups: Luzon, with an area of 142 000 km2; Visayas, with an area of 56 000 km2; and Mindanao, with an area of 102 000 km2. These three groups are further divided into regions, provinces, cities and municipalities, which are further divided into barangays. In 1996, the country had 12 regions plus 3 specific regions, namely the Metropolitan Manila (national capital region), the Cordillera Administrative Region, and the Autonomous Region of Muslim Mindanao. There are 76 provinces, 60 cities, 1 544 municipalities and 41 921 barangays.

The Philippines has a varied topography with highlands and numerous valleys. Its four major lowland plains are the central plain and the Cagayan valley in Luzon, the Agusan valley and the Cotabato valley in Mindanao. These lowlands contrast sharply with the adjacent high mountain areas of the central and east Cordilleras and the Zambales mountains. The highest peaks reach almost 3 000 m above sea level at less than 30 km from the sea.

The total cultivated area is estimated at 9.5 million ha, of which 56 percent for annual crops. The average farm size is 2.2 ha.

In 1996, the total population was estimated at 69.28 million (45 percent rural). The average population density is 231 inhabitants/km2, ranging from 46.9 inhabitants/km2 in Agusan del Sur (Region X - northern Mindanao) to 348 inhabitants/km2 in Region IV - southern Tagalog, a region in Luzon south of Manila, and more than 13 000 inhabitants/km2 in Metropolitan Manila. The average annual population growth is estimated at 2.4 percent.

Agriculture is the prime mover of the country's economy, being at present the least import-dependent activity. From 1988 to 1990, the agriculture sector's contribution to GNP varied around 17 percent. It provided about 30 percent of GDP and generated more than 60 percent of total export earnings. It employed about 41.5 percent of the labour force in 1996.

Climate and water resources


The climate of the country is tropical and monsoonal. It is characterized by uniformity of temperature (average temperature of 27C throughout the year), high relative humidity (above 70 percent everywhere throughout the year except in southern Tagalog where it falls to 65 percent in March/April), low solar radiation, diversity of rainfall and high frequency of tropical cyclones. The main air streams that affect the Philippines are the northeast monsoon from late October to March, the southwest monsoon from May to October and the North Pacific trade winds, dominant during April and early May. Many of the larger islands of the Philippines have high mountain ranges, most of which lie along a generally north-south axis across the paths of movement of the important air streams. Thus, apart from temperature effects due to elevation, the orographic effects of mountains have important influences on regional rainfall patterns by causing increased precipitation on windward slopes and rain shadows in their lee during the monsoon periods.

The average annual rainfall is estimated at 2 348 mm/year as observed from 1961-1990, but this figure varies from 961 mm (General Santos City in southeast Mindanao) to more than 4 051 mm (Infanta in central Luzon). The extreme annual rainfall events ever recorded are 94 mm at Vigan in Ilocos Sur (northern Luzon) in 1948 and 9 006 mm in Baguio City (northern Luzon) in 1910.

The rainfall pattern and annual amount are influenced mainly by altitude and wind. The northwest of the country has a dry season from November to April and a wet season during the rest of the year, i.e. the southwest monsoon. The southeast receives rainfall all year round, but with a pronounced maximum from November to January during the northeast monsoon. In the areas not directly exposed to the winds, rainfall is evenly distributed throughout the year, or there are two seasons but not very pronounced; from November to April the weather is relatively dry while it is relatively wet the rest of the year. The lowest rainfall occurs in the provinces of Cebu, Bohol and Cotabato in the centre of the country.

The archipelago lies in the typhoon belt, and many islands are liable to extensive flooding and damage during the typhoon season from June to December. The frequency of typhoons is greater in the northern portion of the archipelago than in the south. Usually, two or three typhoons reach the country each year.

River basins and water resources

There are 421 rivers in the country, not counting small mountain streams that sometimes swell to three times their size during rainy months. The rivers are an important means of transportation and a valuable source of water for irrigation for the fields and farms through which they pass. There are also 59 natural lakes and more than 100 000 ha of freshwater swamps.

The five principal river basins (more than 5 000 km2) are: the Cagayan River basin in north Luzon (25 469 km2); the Mindanao River basin (23 169 km2) in Mindanao island; the Agusan River basin (10 921 km2) in Mindanao island; the Pampanga River basin (9 759 km2) near Manila in Luzon island; and the Agno River basin (5 952 km2) in Luzon island. Only 18 river basins have an area greater than 1 000 km2: 8 of them are in Mindanao island, 7 in Luzon island, 2 in Panay island and 1 in Negros island. The smallest river basins are frequently under 50 km2.

In order to have manageable units for comprehensive planning of water resources, the National Water Resources Council divided the country into 12 water resources regions. Major considerations taken into account in this regionalization were the hydrological boundaries defined by physiographic features and homogeneity in climate of the different parts of the country. However, in fact, these water resources regions generally correspond to the existing political regions in the country. Minor deviations dictated basically by hydrography affected only northern Luzon and northern Mindanao.

The country's annual average runoff is estimated at 444 km3. In nine years out of ten, the annual runoff exceeds 257 km3.

Groundwater resources

There are four major groundwater reservoirs (Cagayan, 10 000 km2; Central Luzon, 9 000 km2; Agusan, 8 500 km2; Cotobato, 6 000 km2) which, when combined with smaller reservoirs already identified, would aggregate to an area of about 50 000 km2.

Private wells are extensively used in rural areas for domestic purposes. Municipal waterworks wells are drilled by the Local Water Utilities Administration for domestic purposes and deep wells have been drilled by the National Irrigation Administration (NIA) for irrigation purposes.

The groundwater resources are estimated at 180 km3/year, of which 80 percent (145 km3/year) would constitute the base flow of the river systems. The total internal water resources would therefore amount to 479 km3/year. (Detailed water resources information for the Philippines.)


The total dam capacity in 1995 was 4 753 million m3, consisting of about 54 small dams (for a total capacity of 80 million m3) and 6 large dams. In the Philippines, a dam is considered large when the storage capacity exceeds 50 million m3 and the structural height is more than 30 m. Three of the large dams are managed by the National Power Corporation (NPC) (Angat, Ambuklao and Palangui IV for a total capacity of 1 426 million m3), the two largest dams being managed by the NIA (Magat - Magat River Integrated Irrigation System (MRIIS) and Pantabangan - Upper Pampanga River Integrated Irrigation System (UPRIIS) for a total capacity of 3 196 million m3). One large dam (La Mesa, 51 million m3) is managed by the Metropolitan Waterworks and Sewerage System, which is also responsible for the management of a small dam (Ipo with a capacity of 36 million m3). The NPC is also in charge of three small dams (Agus II, IV and V for a total capacity of 27.7 million m3) while all other small dams have been created with various objectives within the framework of the small water impounding management (SWIM) projects, which are implemented by several agencies.

A survey of surface water storage potential has identified sites for 438 major dams and 423 smaller dams.

Water withdrawal

The total water withdrawal was estimated on the basis of the water rights issued by the National Water Resources Board (NWRB) to 55 422 million m3 in 1995, of which 88% is for agricultural purposes, 8% for domestic and 4% for industry (figure 1). Other water withdrawal (non-consumptive use of water) included hydropower (89 000 million m3), fisheries (498 million m3) and recreation (93 million m3).

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Production of wastewater in the national capital region and nearby provinces is estimated at 74 million m3, while the volume of treated wastewater reached 10 million m3 in 1994 at the Ayala and Dagat-Dagatan pond. Disposal of wastewater is expected to increase as new sewer lines are being built every year.

Irrigation and drainage development

The irrigation potential was estimated at 3.1 million ha in 1990. It corresponds to the area where irrigation facilities can easily be provided by the Department of Agriculture or the NIA. The primary definition of irrigation potential in the Philippines is land on slope less than 3 percent (this criterion might be violated by including somewhat steeper land if it is already terraced for paddy cultivation and water could be easily delivered). A World Bank survey has proposed the reassessment of irrigation potential as the figure of 3.1 million ha was obtained without considering new settlement on agricultural lands, water resources availability, water resources development cost, need of flood control and drainage facilities, etc.

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Although irrigation development in the Philippines was undertaken by rural communities (Banawe terraces, cooperative irrigation societies (zinjara) and lowland schemes near Manila) in earlier centuries, the major irrigation investment periods have been the 1920s, the post-war period and the 1970s and early 1980s when public involvement in the irrigation subsector was at its maximum. In this respect, the creation of the NIA in 1964 has been decisive.

In 1992, the area of land equipped for full/partial control irrigation was estimated at 1 532 751 ha. Irrigation water is generally supplied by river diversion (Figure 2).

An inventory refering to 1993 reports that the area equipped for irrigation for the 12 regions adds up 1 550 000 ha. Information regarding the distribution of irrigated areas as established for the Map of Irrigated Areas for South East Asia can be found here.

There are three types of irrigation systems in the Philippines (Figure 3): national irrigation systems (NIS), communal irrigation systems (CIS) and private schemes.

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NIS schemes (646 519 ha in 1992) have been constructed and are operated and maintained by the NIA. The cost of the system is borne entirely by the NIA; farmers have to pay fees to cover O&M expenditure. There are about 150 NIS schemes spread throughout the country. Three main sub-types coexist, differing by water origin:

  • Three large schemes (Magat, for a total area of 80 977 ha; Upper Pampanga, 94 300 ha; and Angat Maasim, 31 485 ha) are backed by multipurpose reservoirs. Although classified as single entities, they are actually conglomerates served by multiple diversion structures which also utilize supplies from uncontrolled rivers crossing the irrigated area. Parts of the service area may be too high to be commanded by the reservoir and are commanded by pump schemes. In 1989, the cropping intensity on these schemes was about 89 percent during the wet season and 78 percent during the dry season.
  • Run-of-the-river diversion schemes, most of them relatively small. These diversion schemes can be fairly complicated in detail, with several intakes and re-use systems which often develop over time in response to observed drainage flows. The largest schemes are located in the alluvial plains. In 1989, the cropping intensity on these schemes was about 72 percent during the wet season and 54 percent during the dry season.
  • Pump schemes. There are seven schemes irrigated only by pumps (about 10 200 ha are equipped), and five large NIS schemes served mainly by gravity flow but which use pumps for a part of their equipped area (about 12 800 ha).

CIS schemes (734 104 ha in 1992) have been created either by the farmers themselves over the centuries, or more recently by the NIA and then turned over to the irrigation associations for O&M. There are about 6 200 communal schemes, 46 percent of them in the province of Ilocos (northwest Luzon), which reflects a long history of irrigation through private initiative in this area. These schemes are predominantly diversion schemes, although a few are served by small reservoirs built within the framework of the SWIM projects. The average size of the communal schemes is about 115 ha, but ranges from 40 to 4 000 ha. The smallest schemes are found in north Luzon, while in Mindanao island these schemes are generally large, many of them being implemented by the government settlement programmes and then transferred to farmer groups. The association bears 10 percent of the direct cost of construction, and pays back the balance within 50 years at a 10 percent interest rate.

Private schemes (about 152 128 ha in 1992) are generally supplied through pumping. They find their origin in publicly assisted river lift and groundwater development projects. In the past, private sugar cane plantations used sprinkler irrigation, but the figure for the total area equipped with sprinkler irrigation is not available. In 1980, public involvement in this sector ceased because of the high cost of energy needed to operate these systems. Most of the schemes have been abandoned or are now inoperable. Of the 379 public tube-wells constructed in 1971, only 22 were still in operation in 1990. Private development of shallow groundwater which started in the 1980s has proved more successful in favourable locations. These schemes are generally devoted to vegetable production during the dry season and to supplementary irrigation to paddy during the wet season. Pump schemes located along rivers have also been developed by private owners serving up to about 20 ha. Although this can be successful when supporting high value crops, many are no longer used largely due to the high cost of O&M, particularly for paddy. Figures on the total area of private schemes are generally unreliable as they are based on the last inventory of pump schemes in 1980. The figure of 152 128 ha should therefore be considered with caution. It is known that this figure includes areas which have been abandoned since 1980, but it does not include new private schemes developed along rivers or using pumped groundwater.

There are two cropping seasons in the Philippines. In principle, all schemes have been designed, both in terms of equipped area and canal capacity, to provide supplementary irrigation to the entire irrigable area during the wet season. The area actually irrigated during the season should thus be 100 percent. In practice, this level is never reached due to many reasons (optimistic design of service areas, flooding and waterlogging in the wet season, complexity of the irrigation system, pump performance, and conflicts between water supply, power and irrigation). The actual irrigated area varies significantly from one season to another, but it is always much lower than the area equipped for full/partial control irrigation.

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Between 1979 and 1992, the area equipped for irrigation increased substantially. It increased by 36 percent in the NIS, and by 33 percent in the CIS (Figure 4). However a survey on the cropping intensity in the NIS schemes shows that the percentage of the area actually irrigated during that period remained approximately constant (70-80 percent for the wet season, and around 60 percent in the dry season). The cropping intensity is known to be even lower in the CIS schemes. The table below shows the cropping intensity in 1992 in the different schemes.


The development of irrigation has resulted in substantial increases in crop yields, as it has coincided with the introduction of HYVs, particularly for paddy. The main irrigated crop is paddy, which is cultivated throughout the country during the wet season, and in some areas during the dry season when other crops with higher added value are also grown. In 1992, almost 45 percent of the total paddy harvested area was irrigated, generating about 57 percent of output (Figure 5). The yields are much lower (30-40 percent) in the communal schemes than in the national schemes, because the water supplies are more uncertain in the small catchment areas where communal schemes are located. On average, the 1992 yield for irrigated paddy was estimated at 3.34 t/ha/season, which was 2.9 times the average yield of irrigated paddy in 1961. For rainfed paddy, the 1992 average yield was estimated at 2.07 t/ha, which is twice the 1961 average yield.

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On all NIS schemes, the fees collected by the NIA should cover the costs for operation, maintenance and even the investment cost within a reasonable period of time to an extent consistent with government policy. However, in practice, capital cost recovery is confined to the communal sector and the fees collected covered only 80 percent of O&M expenditure in 1989. The average cost of O&M varies significantly: using the large schemes as an example, it was about US$31 in the Magat scheme and US$18 in the Upper Pampanga scheme in 1992.

The fees are expressed in kilograms of paddy, calculated by season and differ according to the origin of water. In diversion schemes, the fee is 100 kg/ha for the wet season and 150 kg/ha for the dry season. In reservoir systems, it rises to 125 and 175 kg respectively, and in pump schemes the fees are 190 kg and between 250 and 600 kg respectively. The fees can be paid either in paddy or in cash. For crops other than paddy, the fees are calculated on the basis of 60 percent of the rate of rice fees.

Under the NIS schemes, the average cost of irrigation development is estimated at US$3 800-7 600/ha for new schemes, while the cost for the rehabilitation of existing schemes varies from US$1 000 to 1 600/ha.

In most schemes, drainage water from one field goes into another field downstream either through the irrigation canal or directly. It is, therefore, difficult to estimate the drained areas in the Philippines. As drainage facilities have been installed only on irrigated schemes, the figure of 1 532 751 ha can be considered as a maximum for the drained area.

The main area subjected to floods is the central region of Luzon, namely the Pampanga, Zambales and Tarlac provinces. About 1 069 000 ha have been identified as flood-prone areas.

The population affected by water related diseases in 1989 was 782 193. These water related diseases include gastro-enteritis, schistosomiasis and hepatitis.

Institutional environment

The NWRB coordinates the activities of the different agencies involved in the water sector (irrigation, hydropower, flood control, navigation, pollution, water supply, waste disposal, watershed management, etc.).

The others main agencies involved in water resources management are:

(i) in water supply and wastewater:

  • the Metropolitan Waterworks and Sewerage System (MWSS) of the Department of Public Works and Highways (DPWH), which is responsible for water supply, storage, treatment, research, design, construction and maintenance of water supply and sewage systems in the national capital region and outlying service areas in nearby provinces;
  • the Local Water Utilities Administration (LWUA) of the Department of Public Works and Highways (DPWH), which is responsible for the development and improvement of water and sewerage systems in areas not covered by the MWSS.

(ii) in water resources monitoring and development:

  • the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA), which conducts monitoring, data gathering and maintenance of information on rainfall and evaporation;
  • the Bureau of Research and Standards (BRS) of the DPWH, which is engaged in monitoring and studies of water resources as well as water research and quality standards. The DPWH is also responsible for flood control;
  • the NPC, which conducts water resources monitoring, research and hydropower generation.

(iii) in irrigation:

  • the NIA of the Department of Agriculture, which was created in 1974 with the mandate to initiate an 'irrigation age'. Its tasks include the development, operation and maintenance of irrigation systems throughout the country. In particular, it has been responsible for the construction of NIS schemes, and is now responsible for the recovery of irrigation fees.
  • the Bureau of Soils and Water Management (BSWM) of the Department of Agriculture, which handles, through its Project Management Office (PMO), the construction and maintenance of SWIM projects.

The SWIM projects have been implemented by the Government to mitigate damage brought about by insufficient water supply during the dry season and the frequent floods during the rainy season. The objectives might differ from one project to another, and the following agencies are involved: the DPWH, for water supply, inland fishing and mini-hydropower; the NIA, for irrigation; the Forest Management Bureau (FMB), for watershed management with an incidental purpose of flood control; and the National Electrification Administration (NEA), for mini-hydropower generation.

The 1976 Water Code of the Philippines revised and consolidated the laws governing the ownership, appropriation, utilization, exploitation, development, conservation and protection of water resources which are subject to government control and regulation through the NWRB.

Trends in water resources management

The majority of the population depends on agriculture for its livelihood and irrigation is considered a crucial element in agricultural production. With the potential irrigable area of 3.1 million ha, irrigation development is only at the halfway stage. Self-sufficiency in food has been set as a target by the Government. Agricultural development through irrigation, therefore, still remains a priority on the Government's agenda.

The Irrigation Crisis Act (Republic Act No. 6978) signed into law in January 1991, mandated the NIA to develop the remaining 1.5 million ha of irrigable lands within ten years through the construction of irrigation projects including other related project components. Irrigation, soil and water management have been set as a priority on the agenda of the Department of Agriculture. The Medium Term Philippine Development Plan (1994-98) also envisages a fast pace in irrigation development.

However, there are numerous economic and environmental problems.

There is growing water competition among the users: water supply, hydropower, environment, fishing and watershed management are competing with irrigation for water. The NWRB was established in order to coordinate the use of water for the different purposes, but its action is hampered, in part, by a lack of reliable data on present water resources and water use.

Erosion and siltation of the canals have resulted in high costs for the O&M of irrigation schemes, and many are thus in need of frequent rehabilitation. The conversion of agricultural lands to industrial or residential use has significantly reduced the area equipped for irrigation which can actually be used for irrigated agriculture.

The high cost of energy hampers the development of pump irrigation systems. The present pump systems are no longer economically viable if devoted solely to paddy.

In addressing these challenges, the NIA, together with the Department of Environment and Natural Resources, is expected to:

  • fully enforce existing laws on environmental protection and conservation, in order to reduce erosion;
  • establish institutional arrangements with the NPC, the NEA and the electric cooperatives to reduce power rates for pumps as a government subsidy to small farmers;
  • work with the Department of Agrarian Reform, under the Comprehensive Agrarian Reform Law, to approve or disapprove the transfer of agricultural lands to non-agricultural uses.

Main sources of information

Galvez, J.A. 1990. Management arrangements for diversifying the inherently rice crop-based irrigation systems in the Philippines. In Management arrangements for accommodating non-rice crops in rice-based irrigation systems. Proceedings of the First review and coordination workshop of the research network on irrigation management for crop diversification in rice-based systems, held in Quezon City, 10-14 September 1990. Miranda and Maglinao editors. Quezon City, Philippines.

Metropolitan Waterworks and Sewerage System. 1994. Annual report. Quezon City, Philippines.

National Irrigation Administration. 1991. Annual report. Quezon City, Philippines.

National Irrigation Administration. 1993. Corporate plan 1993-2002. Quezon City, Philippines.

National Statistics Office. 1995. Philippine yearbook 1994-1995. Manila.

National Water Resources Council. 1976. Philippine water resources, first assessment. Report No. 19. Quezon City, Philippines.

National Water Resources Council. 1980. Groundwater of the Philippines. Quezon City, Philippines.

World Bank. 1992. Philippines, irrigated agriculture sector review. Report 9848-PH (in two volumes). Washington, D.C.