This article is part of The Conversation’s series on drought. You can read the rest of the series here.

As California suffers its fourth year of drought, much of the attention is focused on the state’s groundwater – a critical source of water and one that is being stretched.

What’s happening to the state’s groundwater resources during this drought, and how can scientists and policymakers manage it effectively?

New era of water scarcity

One way to think about groundwater is to compare it to dark matter, which is invisible yet accounts for most of the matter in the universe. Similarly, groundwater is invisible yet accounts for about 95% of all circulating freshwater on earth. While the science of groundwater is mostly well-known and tested, the effective management of it, in concert with management of surface water, remains a frontier, like dark matter.

For an analogy closer to home, consider the world of finance. Imagine that all of your money, including retirement funds, is in two bank accounts. The balance, deposits and withdrawals from account A are known, but are largely unknown for account B. Then here’s the kicker: when the balance in account A gets depleted, things change: uncontrolled, largely unknown amounts of cash are withdrawn from account B. How would this financial management strategy work for you? Of course, it would be disastrous, yet this is how we commonly mismanage our interconnected accounts A, surface water, and B, groundwater.

Robert Galbraith/Reuters

Such mismanagement will cause crises, except when account B is flush with cash or water. Indeed, for the last half-century many groundwater systems have been flush enough to cover for lack of water resources management.

Now, however, it is clear that we have moved into a new era of water scarcity driven by growing world population and water demand that is exposing more groundwater crises across the globe, including the North China Plain, India, the Middle East, Australia and California.

To further complicate matters, our climate already seems to be fulfilling the projections of climate models that indicate futures with more extreme dry and wet periods.

Multiple time scales

The good news is that, like in finance, most water crises are avoidable if we truly manage both surface water and groundwater.

Why has this largely not happened and why is there so little progress in dealing with water crises? I believe a big part of the explanation lies in lack of motivation and lack of transparency about the “accounts.”

There is little motivation to live within our means unless the consequences of our overconsumption are sufficiently clear.

In finance, the obvious consequence is account overdraft and unsustainable debt. Similarly, we refer to excessive groundwater depletion as overdraft, but unlike the finance case, there are multiple negative consequences that emerge over time, some of them more or less immediately, and others on time scales of decades to centuries.

Unfortunately, the short-term consequences are either not sufficiently damaging or not sufficiently noticed to serve as deterrents. By the time the most damaging, long-term consequences occur, however, it can be too late.

Here is a typical sequence of phenomena as groundwater development and overdraft proceed in the thick, alluvial aquifer systems that are common to California and elsewhere:

Groundwater levels decline over a period of months to years, causing somewhat higher energy costs to pump the water. Groundwater levels continue declining year after year, causing still higher energy costs, drying up shallow wells, depleting rivers, lakes and wetlands, and perhaps inducing land subsidence, or sinking, as any silt and clay beds in the aquifer system depressurize and compact irreversibly. In coastal areas, saltwater from the ocean intrudes into the fresh aquifer system, contaminating wells near the coast. Meanwhile, most of the wells in the basin are still able to pump large amounts of potable groundwater. Similarly, severely depleted inland aquifers may begin to draw in poor-quality groundwater residing in the non-aquifer media (ie, the silts and clays that commonly make up a large percentage of the geologic media that compose what we call aquifers) and from deep, saline groundwater systems that underlie the fresh groundwater. After a period of decades, the ongoing overdraft effectively converts the groundwater system into a closed hydrologic basin in which the predominant exit for water is evaporation, resulting in salt accumulation and salinization, likely on a century time scale. (For examples of what happens in closed hydrologic basins, one need look no further than places like Mono Lake and the Salton Sea in California and Great Salt Lake in Utah, all of which are saltier than seawater.) Eventual emptying of the fresh groundwater from the basin.

Is sinking land enough to motivate change?

Now let us return to the issues of motivation and transparency. The negative consequences often do not motivate change because they unfold somewhat complexly on multiple time scales and because the links between our land and water use practices and these consequences are not very transparent or obvious.

For example, consequences one through three on the above list tend to be the most immediate, unfolding on time scales of years or a couple decades. But with the possible exception of seawater intrusion and excessive subsidence, we are often willing to tolerate these.