In Jerusalem, it was a sunny, cool weekend, and in the upper Galilee and the Golan Heights, rainfall was light. But closer to the Mediterranean Sea, in coastal cities like Ness Ziona and Haifa, heavy downpours caused severe flooding, causing firefighters to rescue dozens of trapped or threatened people. Intense rainfall has become more and more common over the past few years.
Israel has reduced ability to deal with rainfall compared with other weather-related issues such as drought, mainly due to rain’s relative infrequency. For water shortages, Israel has developed agricultural irrigation techniques that are imitated widely around the world, as well as desalination plants that turn seawater to drinking water, thus reducing dependency on the Sea of Galilee. But floods stemming from intense rainfall devastate Israel’s coastal regions, leading to many incidents of people being swept away and drowning. The recent increased intensity of rainstorms only exacerbates the problem.
“The answer lies in the Mediterranean,” Dr. Amir Givati, a hydrology expert and former director of Israel’s Water Authority, told Davar. He explained how the warming sea temperatures create more intense rainstorms.
According to Givati, the Mediterranean is warming faster than average. “On average, the earth has warmed less than one degree Celsius,” he explained. “[By comparison], in the Mediterranean Sea, the water temperature has risen two degrees above average for November.”
“The mixture of warm seawater with cold air coming from Eastern Europe creates immense instability,” Givati said. “The air rises very quickly, and storm clouds develop. The result is lightning, thunder, hail, and lots and lots of rain over a short period, near the coast.”
A once-in-a-100-years event has become commonplace
The total amount of rainfall in Israel is declining, as is the number of rainy days per year. The result is shorter and much more powerful rain events.
According to Dr. Givati, instead of measuring precipitation over the course of a season or even over the course of a particular storm, researchers need to examine the hourly rate of rainfall. The hourly rates give clear evidence of the trend toward shorter, stronger storms.
Rainfall this past weekend was highest at Ma’agan Michael, a kibbutz in the north of Israel. A measurement station there recorded about 220 millimeters of rainfall. That measurement, recorded in a single weekend, marks 40 percent of the total rainfall recorded at that station in most years.
Even before the strong rains last weekend, some stations have measured rains of up to 67 millimeters in just an hour or two.
“As someone who has been doing this for two decades, there is no doubt that this trend is due to global warming,” Givati said. “If you look at data from the last 50 years, a rainfall of 50 millimeters in a single hour would have been considered very unlikely, a likelihood of one in a hundred. In the past two years, it’s become commonplace.”
Climate change requires appropriate infrastructure
Climate change will require Israel to build and maintain drainage systems that can cope with more frequent, more intense flooding, said hydrologist and environmental consultant Gilad Sapir. According to Sapir, Israel is not prepared.
In an article published on the website of environmental consulting firm AVIV AMCG, Sapir writes that most planning authorities in Israel do not spend time reviewing new developments’ drainage plans.
“Most authorities do not check the drainage plans submitted to them. Usually it’s because they are understaffed, so they don’t have enough people to actually test out the plans,” he wrote.
Sapir points to an “unholy trinity” of understaffing, underfunding, and a lack of enforceable laws governing drainage as the root of the planning problem. He warns that it is getting riskier and riskier for Israel to continue to deal with floods as they arise, instead of planning ahead.
In recent years, the Water Authority has been working on new ways to mitigate the risk of floods. They now recommend that new buildings be constructed with holes through which rain can seep directly into the water table, without needing to travel through drainage pipes.
This solution, however, will do little to prevent flooding in coastal cities, where the vast majority of buildings are not constructed that way.
Dr. Givati emphasizes how important it is to properly maintain the drainage systems that do exist.
“It's critical," he said. “Tel Aviv, Rishon Lezion and Ness Ziona received about the same intensities and amounts of rain, but the results were much worse in Rishon LeZion and Ness Ziona.”
Still, he said, some cities are already working more proactively to reduce the risk of floods. Following the floods in January this year, the Tel Aviv municipality hired Givati as a consultant.
“Now in Tel Aviv, there is a warning system for drainage problems. The municipality prepares in advance and responds very quickly to any malfunction,” he explained.