Groundwater, which is found in aquifers below the surface of the earth, is one of our country’s most important natural resources. 70 percent of the drinking water that Santa Ana supplies to residents comes from groundwater.
Why Groundwater Reserves Are Important
While the state of emergency is officially over in most of California, the effects of the drought will take years to recover. Why? Unlike surface water (rivers, lakes and reservoirs), which can recover during a heavy rain season, groundwater sources recover far slower, often taking years or decades to be replenished.
What are groundwater sources and why does it take so long to replenish them? To answer this question, it’s important you understand our earth’s water cycle, also known as the hydrologic cycle.
It describes how water evaporates from the surface of the earth, rises into the atmosphere, cools and condenses into rain or snow in clouds, and falls again to the surface as precipitation. The water falling on land collects in rivers and lakes, soil, and porous layers of rock (aquifers), and much of it flows back into the oceans, where it will once more evaporate.
You can refer to the illustration above to read more about the five processes that makeup this cycle:
- Evapotranspiration: Surface water that accumulates in lakes, ponds and oceans is heated by the sun and evaporates, returning moisture to the atmosphere, while plants return water to the atmosphere by transpiration.
- Condensation: As water vapor cools, it condenses to form clouds, which can result in precipitation.
- Precipitation: Clouds lose their water as rain or snow through precipitation, which falls to the earth’s surface.
- Runoff: Precipitation is either absorbed into the ground or flows overland as runoff into streams, lakes and the ocean. Runoff can also come from snow packs that thaw and melt in the spring.
- Infiltration: Some water moves downward or infiltrates through cracks and pores in soil and rocks until it reaches the water table where it becomes groundwater and replenishes the aquifer. The infiltration is measured as inches of water-soaked by the soil per hour. Groundwater is pure and drinkable.
The water cycle provides a reliable supply of water by annually replenishing or recharging surface and groundwater sources. The winter storms certainly benefited some Southern California reservoirs like Castaic Lake, which rose to about 96% of capacity, and Diamond Valley, which more than doubled its capacity from about a year ago.
However, heavy rainfall doesn’t necessarily translate into more water for aquifers. With shorter, intense rainfall like our last winter storms, there is less of an opportunity for water to infiltrate into the ground. Rather, it runs off fast into rivers and out to sea. Our groundwater supply is far from recovered, and many of Southern California’s groundwater reserves are severely depleted.
As such, all Californians are encouraged to make water conservation a way of life by not wasting this precious resource. In doing so, we will help build up our reserves and meet future demands.