The Southeast Asian Regional Center for Graduate Study and Research in Agriculture (Searca) has warned over the increased risk of groundwater supply depletion by 2050.
The study, which was funded by Searca, was conducted by Dr. Victor Ella of the University of the Philippines-Los Baños (UPLB) simulating the effects of a high temperature and low precipitation regime in Bay, Laguna—an existing shallow aquifer that has supplied water for irrigation and domestic use for hundreds of years.
Searca noted that the Bay aquifer was an ideal site since it had five alternating layers of clay, fine sand, clay, coarse sand and with the total thickness of the five layers at 15 meters.
Searca Director Gil Saguiguit Jr. said that the study was the first of its kind in the country, and added that the method used by Ella was the most advanced computer-aided analysis of the flow, discharge, recharge and the impact of precipitation on the rows, layers and other groundwater sources.
Saguiguit stressed that the Ella study on groundwater was a significant contribution to the ongoing campaign by government to conserve water or use it responsibly.
The study also has a direct impact on the use of shallow tube wells (STW) for irrigating farms, he explained, and should offer policymakers an empirical basis for formulating a policy on the sustainable extraction of groundwater.
For his part, Ella said that studies of groundwater depletion have been scarce and argued that the Bay, Laguna, analysis will provide the empirical basis for a judicious policy for sustainable water supply now and in the future.
In the face of increasing population and economic development coupled with unreliable water sources like rivers and streams especially in the dry season, Ella pointed out that the Philippines is a heavy user of groundwater for domestic, agricultural, industrial and other purposes.
During the assessment, Ella said that he used the US Geological Survey Three Dimensional Modular Finite-Difference Groundwater Flow Model that was developed by M. G. McDonald and A. W. Harbaugh in 1988.
He explained that the higher and lower air temperature scenarios from the Intergovernmental Panel on Climate Change (IPCC) that he used gave him the opportunity to predict groundwater losses.
“In a low temperature condition, the model showed that groundwater levels will decline at average rate of 0.10785 meter, 0.11286 and 0.11294 meter per decade of zero [percent], 10 [percent]and 20-percent decrease in annual precipitation, respectively,” he said.
“This could mean that by the end of 2050, groundwater levels are likely to decrease by 0.43138 meter, 0.45143 meter and 0.45177 meter if rainfall decreases by zero [percent], 10 [percent]and 20 percent, respectively,” Ella added.
“Using the high temperature increase scenario, the model predicted a 0.43924 meter, 0.45 meter and 0.45439 meter decrease in annual precipitation reduction scenarios, respectively. This corresponds to a decadal groundwater decline of 0.10981 meter, 0.11250 meter and 0.11360 meter,” he said.
Ella also noted that the data he had collected showed rising minimum and maximum temperatures in Bay from 1960 to 2008.
The local temperature pattern hews closely to the IPCC temperature trends published in 2007, he added.
“The trend in annual precipitation also appeared to be erratic on a yearly basis. However, decadal trends indicate a general decrease in average annual rainfall. The average annual precipitation decreased by 6.2 percent from the 1970s to the 1980s and by 13 percent from the 1990s to the present decade,” Ella said.
For the current decade, the average annual precipitation is lower than the three previous decades, he stressed.
The study has policy implications on STW irrigation in the country as well, noting that declining groundwater levels due to climate change affects not only the pumping rates, but also the design and installation of STWs and pumping units.
“Lower groundwater levels are further aggravated by other factors such as land use change, improper well sitting, well interference and excessive unregulated pumping, all of which increase the operation and maintenance costs shouldered by the farmers or private operators,” Ella concluded.
The study was funded by the Searca’s Seed Fund for Research and Training (SFRT), a competitive grant that provides up to $15,000 to promising researchers and trainers with limited funds to enable them to carry out initiatives that support agricultural and rural development. Of the 65 SFRT grantees to date, 24 are Filipinos.
James Konstantin Galvez