22/10/2026
The Effects of El Niño and the Importance of Deep Well
For groundwater projects in the Philippines, El Niño is particularly important because it can reduce groundwater recharge, lower water levels in wells and cause existing wells to produce less water or dry up temporarily.
However, a deep well is not automatically better than a shallow well. The best choice depends on the local geology, the depth and thickness of water-bearing formations (aquifers), groundwater recharge and the required water supply.
1. What are the effects of El Niño on groundwater?
El Niño is a climate phenomenon associated with changes in Pacific Ocean temperatures that can cause hotter and drier conditions in the Philippines, particularly during affected seasons.
Its effects on groundwater include:
💧Reduced groundwater recharge. Less rainfall means less water infiltrates the soil and replenishes aquifers.
💧Declining groundwater levels. The water table may fall as groundwater discharge and pumping exceed recharge.
💧 Reduced well yield. Pumps may produce less water, and shallow wells may run dry.
💧 Increased pumping costs. A deeper water level may require more energy to pump water.
💧 Worsening water quality. Lower groundwater levels can concentrate some dissolved contaminants. In coastal areas, excessive pumping may also increase the risk of saltwater intrusion.
💧Greater competition for water. Households, farms and businesses may depend more heavily on groundwater when surface-water supplies decline.
One important distinction: groundwater levels may respond to drought over weeks or months, while deeper aquifers may respond more slowly. Deep aquifers can also decline during prolonged drought, especially where pumping is heavy or recharge is limited.
2. Why a deep well may be more advantageous during El Niño
A properly designed deep well can have three important advantages:
💧Greater drought resilience. If it reaches a deeper aquifer that is less directly affected by seasonal rainfall, it may continue supplying water while a shallow well's water level declines.
💧 More reliable water supply. A productive aquifer with adequate saturated thickness and permeability may sustain pumping more consistently.
💧 Potentially better protection from surface pollution. Thick, low-permeability layers above the aquifer can reduce the movement of some contaminants from the surface.
3. What should be done when planning a well during El Niño?
For a groundwater development project, we recommend the following approach.
1. Conduct a geophysical survey. Use electrical resistivity surveying, such as Vertical Electrical Sounding (VES), to identify subsurface layers that may be favorable for groundwater.
2. Interpret the local geology. Distinguish potentially water-bearing formations from clay, compact rock, and other formations that may have limited groundwater productivity. Resistivity alone cannot confirm a productive aquifer.
3. Determine the target depth based on the survey and nearby well records. Do not select a drilling depth based solely on the assumption that deeper is better.
4. Conduct a pumping test after drilling. Establish the sustainable pumping rate, drawdown and recovery characteristics.
5. Test water quality. Check suitability for the intended use, particularly drinking, domestic supply or irrigation.
6. Monitor groundwater levels. Record static water level, pumping water level, and seasonal changes to help assess the well's resilience during drought.
PAGASA's October 7, 2026 advisory indicates that El Niño is expected to persist into the first half of 2027 and may peak before the end of 2026. This makes groundwater assessment and responsible pumping particularly important.
