Lack of fresh drinking water poses a serious problem for the one million residents of the Gaza Strip, who live and grow food in an area one-tenth the size of Rhode Island. They draw water for drinking and agricultural irrigation from aquifers on the Mediterranean that are becoming saltier each year.
The United Nations Development Programme and United States Agency for International Development currently recommend that Gaza can maintain its freshwater supply by using only an amount less than or equal to that of its usable annual rainfall. But a study presented by MIT researchers at the December meeting of the American Geophysical Union shows that even if the residents stay within those quantity guidelines, the quality of the water will continue to deteriorate rapidly.
Because of saltwater intrusion from the sea into the aquifer, and recirculation and evaporation losses of pumped groundwater, the quality of the water is deteriorating faster than fresh rainwater can desalinate it. This means that Gaza residents must acquire water from beyond their borders, which are closed at present; build a large desalination plant; or eliminate agriculture within the next two decades, said the two researchers, Assistant Professor Charles Harvey and Dr. Annette Huber-Lee of the Department of Civil and Environmental Engineering.
"We're not talking about a hundred years into the future," said Dr. Huber-Lee, lead author of the study. "I can show numbers that say it's a problem very soon. It's reaching a point where you have to decide what you are willing to impose upon people, and without additional sources of water, you finally have to eliminate agriculture."
Agriculture is about 30 percent of Gaza's gross domestic product. While this percentage hasn't decreased in the past 20 years, the increasing salinity has affected the types of food grown, eliminating most citrus fruit -- which is sensitive to saline -- in favor of salt-tolerant vegetables and flowers.
The aquifer acquires salt in several ways. One way is seawater intrusion, which occurs when water is overpumped from the aquifer, allowing seawater to seep in underground to fill the emptying reservoir. Another is from brackish upstream sources, and another way is from the evaporation of irrigation water and wells that recapture irrigation water, preventing it from flowing back into the Mediterranean. (As some of the water used to irrigate fields evaporates into the air, salt is left in the soil. That salt is then carried by irrigation water back into the aquifer, increasing the salinity of the aquifer with each cycle.)
"Families send kids out with two-liter Coke bottles to get water that is less salty for drinking. When they give you a cup of this water, you can certainly taste the salt, but it's drinkable," said Dr. Huber-Lee. "Still, the older people say to me, 'When I was younger, all this water was fresh.'"
Dr. Huber-Lee and Professor Harvey built optimization computer models to predict freshwater availability in the Gaza Strip by incorporating numerical modeling of groundwater flow and salt transport in the region with a quantitative economic model of the region's domestic and agricultural water use.
Assuming that the Gaza regional government followed international agencies' recommendations of using only the amount of water renewed by annual rainfall (10-20 inches), the population of the Gaza Strip still would run dangerously low on fresh water within a decade, the researchers said.
"Our simulation models indicate that current water use in Gaza is unsustainable with the current population. The steady-state sustainable model shows an extreme solution: eliminating irrigated agriculture and reducing household water use," said the researchers.
The steady-state model, a type of model used more frequently by environmentalists than economists, calculates what actions can be taken that will be sustainable in the long run. The MIT model shows that the irrigation of crops would have to be stopped immediately and household water use curtailed to sustain water use into the future.
The researchers' "transient" model looked at how to use the water effectively from year to year. This type of model is the standard approach for evaluating the costs and benefits of water management plans over time, and it places a higher value on agricultural use of water today, regardless of what effect that has on the future.
"The 75-year transient model shows that irrigated agriculture can remain, but leaves the groundwater too saline for future generations to use," the researchers said in their paper.
"The solution is desalination or other new sources of freshwater, together with infrastructure to transport and treat water," said Drs. Huber-Lee and Harvey. They estimate that a desalination plant large enough to do the job -- one that could process 50 million cubic meters per year -- would cost at least $100 million per year to build and have operational costs on the order of $0.70 per cubic meter of water.
The researchers used data obtained from scientific literature and the Palestinian Ministry of Agriculture. The research was funded by grants from the Dutch Foreign Ministry and the US Environmental Protection Agency. Dr. Huber-Lee, who earned the SM at MIT in 1987, began working on the Gaza water project while doing her doctoral work at Harvard. She completed the project while working at MIT with Professor Harvey, who was on her doctoral committee.
A version of this article appeared in MIT Tech Talk on January 10, 2001.