Home Articles El Nino damage assessment in central Luzon using multitemporal remotely- sensed images

El Nino damage assessment in central Luzon using multitemporal remotely- sensed images

Juanito G. Berja Jr.
Department of Geodetic Engineering
University of the Philippines
1101 Diliman, Quezon City, Philippines
E-mail: [email protected]

Abstract
In the Philippines, as in other Southeast Asian countries, adequate supply of water for irrigation is significant for ensuring consistent high yields. This phenomenon becomes even more significant with the occurrences of El Nino-related droughts in the region. Using multi-temporal remotely-sensed images (MOS-1 and ADEOS), the study looks into the effect of El Nino-related drought on agricultural productivity in Central Luzon.

Introduction
Central Luzon is the rice granary of the Philippines with an economy that is propelled mainly by agriculture (1998 Philippine Yearbook). With a total rice land area of 530, 463 hectrares, the region produces about one-third of the harvest of the country (Salita, 1997, Huke and Kuke, 1997). In 1990, the total rice production of the area was 1,875,909 metric while in 1994, rice production was reduced to 1,197,855 (Provincial Rice Statistics, 1995).

In Central Luzon, as in other parts of the country, the biggest problem faced by farmers is the lack of adequate control of water, both in the amount available and in distribution throughout the growing season. It is the most serious physical constraint to consistently high yield (Huke and Huke, 1997). One reason for this problem is the lack of systematic irrigation network in the area. These phenomena led to the development of several water control-based schemes. Based on these schemes, agricultural lands in the area were classified as (a) irrigated wet and dry season and (b) non-irrigated wet and dry seasons.

According to Huke and Huke (19997), an irrigated wet season refers to areas to which water may be added using a source other than local rainfall or local runoff while an irrigated dry season refers to areas subject to the addition (or removal) of water during the local dry period. On the other hand, non-irrigated wet and dry seasons will be referred in the study as areas that are rainfed or watered by deep well either during the wet or dry seasons.

The effects on agricultural yields of the lack of adequate water supply for irrigation are aggravated whenever El Nino is experienced in the area. In 1997, Central Luzon was one of the hardest hit regions of El Nino-related drought events in the country. Lack of rain since the supposed onset of the rainy season in the month of May delayed the planting season. In other cases particularly in the rain fed areas farmers have not planted rice. This situation was also experienced during the 1990 El Nino occurrence (Morales, 1997)

Objectives
The study utilized multitempral MOS-1 and ADEOS images to map the extent of irrigated lands affected by the El Nino phenomenon.

Specifically, the study aims to: (a) present the conditions in the study areas when El Nono was severely felt and when it was not; (b) measure the extent of El Nino damages and the relative decline in productivity of the agricultural land in Central Luzon: and (c) provide valuable information about El Nino to policy makers which can be used in formulating appropriate plants and programs to avoid or mitigate the impact of this hazard.

Study Area
San Fernando is the capital of the province of Pampanga. It has a total farm land area of 635 hectares. It is fast developing area that for a long time has served as the administrative capital of Central Luzon. It is approximately 60 kilometers away from Metro Manila.
  

The El Nino Phenomenon
El Nino is a large scale oceanographic phenomenon that develops in the pacific Ocean, and which is associated with extreme climatic variability. It is the invasion from time to time of warm surface waters from the western equatorial Pacific Basin to the eastern equatorial region and along the coasts of Peru and Ecuador. This condition can prevail for more than a year causing anomalous atmospheric circulation in the tropical Pacific; thus, resulting to heavy rains or strong winds in some areas and drought in other. It can adversely affect the economy in both the local and global scale.

In the Philippines, the effect of El Nino has always been associated with droughts. But the expected second and third order impacts include a number of environmental, social and economic effects. Examples of environmental effects include degradatin of soil which could lead to desert-like conditions if persistent effect on water quality like salt-water intrusion, high forest/grass/bush fire risk and domestic water supply shortage.

Based on the records of the Philippine Atmospheric. Geophysical, Astronomical Services Administration (PAGASA), the pattern of El Nino recurrence in the country is at least every three to five years from 1968-1987. During this period there were five drought events recorded (1968-1969; 1972-1973; 1976-1977; 1982-1983 and 1986-1987).

The frequency of recurrence intensified starting late 1980s, with the earlier interval of three to five years trimmed down to just tow years and one year of the following decade. For instance, it took a two-year respite before El Nino recurred in 1989 following the 1986-1987 drought event, the last warm episode to happen within a two-decade period from 1969 to 1989.

The worst El Nino event to hit the country in terms of areas affected was during the 1982-1983 period but the longest and worst (in terms of damages) El Nino event happened in 1990-1995. The drought, which started in late 1989, actually took off in 1990 as a separate episode which later baffled climatologists because of its protracted lifespan.

The said event lasted up to 1995, lying dormant for a shore while in 1993 when the country experienced a record-breaking number of tropical cyclonesentering the Philippine area of responsibility. That year, there were a total of 33 tropical cyclones, way above the normal, which is 20 per annum. But to note, this was this was the first time that an El Nino related drought was prolonged. The 1990-1995 warm episode had some similarities in terms of duration to an El Nino event that occurred in 1935.

Some climatologists think that the 1997-1998 warm episode would likely to follow the 1982-1983 drought events in terms of intensity and areas covered because of the high positive anomaly of the sea surface temperature.

Methodology
Two multitemporal remotely-sensed images (MOS -1 and ADEOS) were acquired to assess the impact of El Nino on the agricultural lands of San Fernando, Pampanga. The images were taken during the wet and dry seasons, respectively, of the years when El Nino affected these areas.

Based on a 1:50,000-scale map, the images were rectified using the ER Mapper software. To generate a map showing the agricultural and non-agricultural lands of the study area for 1990 and 1997, the images were classified using the unsupervised classification technique. Then to show the irrigated and non-irrigated areas of each image, both images were classified using the supervised technique. To determine the relative changes in land use between 1990 and 1997, the images were overlaid. The accuracy of the information generated was checked through ground truthing.

 

 

 

Analysis and Interpretation of Data
An analysis of the classified images revealed the different land uses of the study area. The 1990 and 1997 images showed substantial agricultural land uses. Most agricultural lands were planted by rice. Most of the lands can be considered as irrigated wet and dry.

As for the non-agricultural land uses, the most prominent in the 1990 and 1997 images is the built-up areas surrounding San Fernando.

In both years (1990 and 1997), the effects of El Nino on the agricultural lands were obvious. The images showed that a large part of the agricultural lands were not cultivated because of the lack of rain and water from irrigation systems. The 1997 images show that rainfed lands and most of irrigated lands were not planted with rice. For the irrigated supply from the water dams servicing the area. For instance, water level in the Pantabangan Dam in Nueva Ecija dropped to 181:7 meters above sea level, or 39.3 meters below the desired level. Likewise, water in the Angat Dam in Bulacan dropped to 185.58 meters from its normal level of 212 meters (Reuter, 1997). Both dams supply water to irrigate agricultural lands in Central Luzon.

In terms of the changes in land use, the effect in agricultural lands in 1990 was greater in area than for non-agricultural lands. In 1997, there was a relative decrease in area of cultivated areas in San Fernando. This meant decrease in agricultural production. Also, there was a decrease in the volume of fish catch because most ponds dried up (Morales, 1997).

While the images reflect a minimal increase in built-up areas between 1990 to 1997, cultivated areas decreased because of the entry of lahar from Mt. Pinatubo in portions of the study area. Another factor is the destruction of irrigation systems in the area due to flooding. A third factor is the reduction of the volume of water supplied by the dams for irrigation.

Conclusion
The study generated up-to-data land use maps showing affected and non-affected agricultural lands of the study areas. Based on the maps, it can be concluded that the agricultural lands of San Fernando decreased in area from 1990 to 1997.

The factors that affected the decrease in the areas of agricultural lands include the lack of adequate water supply, especially during the occurrence of El Nino, encroachment of lahar and land conversion. The decrease of cultivated agricultural lands translates to a corresponding decrease in agricultural production. Other factors that led decrease in agricultural production include lack of systematic irrigation network and lowering of water levels in most dams.

Acknowledgement
The author gratefully acknowledges the kind assistance of NASDA RESTEC of Japan for the availability of the MOS-1 and ADEOS images.

References

  • Balababa, L. et. al. Identification of Rice Cropping Areas in the Mekong Delta using Radar Imagery. Earth observation Quarterly. European Space Agency, December 1997.
  • Huke, Robert E. and Eleanor H. Huke. Rice Area by Type of Culture: South, Southeast and East Asia. Manila: International Rice Research Institute, 1997.
  • Morales, Leticia. Warms weather ahead as El Nino returns. Manila chronicle. Manila, 27 July 1997, pp. 10-11.
  • Philippine Atmospeheric, Geophysical, Astronomical Services Adminstration. EL NINO Pamphlet. Quezon City: DOST-PAGASA, 1994.
  • Reuter. Levels of five major dams dip due to “below-average” rainfall. Business World. Manila, 14 August 1997, p. 16.
  • Salita, Domingo C. Geography and Natural Resources of the Philippines. Quezon City: JMC Press, Inc. 1997. 1998 Philippine Yearbook.