Local rainfall stats defy global warming fears
Despite warnings that global warming is already impacting precipitation quantities, local rainfall statistics have remained essentially unchanged in the 60 years they have been tracked.
"While models project gloom and doom for climate change, field observation of rainfall indicates a grayer stability," according to Haifa University's Noam Halfon. The institute's geography department recently completed research that found no substantial change in rainfall quantities.
Over the past two years, Halfon examined all the monthly rainfall data amassed by the Meteorological Service since the establishment of the state. In addition, researchers looked at daily rainfall statistics from 30 meteorology stations and reports of unusual climatic events. The research covered the area of the country north of the desert line (north of the Negev) to preserve the reliability of data over years.
According to the research, rainfall in the examined area has remained stable. Average monthly rainfall data showed no clear trend change for any particular month, nor was the rainfall distribution between seasons different over time.
Average annual rainfall has not changed in the period Halfon examined. "Data from certain stations showed increased localized precipitation - mostly in the eastern and southern coastal plain," he said. "In other areas, figures showed a slight drop in rainfall quantities, mostly in the North and East. No area showed a clear change."
Frequent warnings of future extreme climatic phenomena like drought years and diminishing rainfall, have not been fulfilled in Israel. The deviation from multi-year rainfall averages has not increased in either direction in recent decades.
The longest drought in the past 60 years was a six-year period in the late '50s and early '60s and not in the last decade. The longest sequence of rainy seasons that approached the multi-year average were the past four winters (2003-2007) although all four deviated slightly underneath the average.
Additional concerns regarding fewer rainy days and a parallel increase in rainfall on individual days also were not found accurate, with no change in light rain versus heavy rain days. Halfon noted it is therefore not surprising that the single-day rainfall record in Israel is from 1921.
"The common belief that weather events are becoming more extreme can therefore be attributed to greater press coverage of weather events, in particular extreme events, and not to an increase in these events," Halfon said.
According to Dr. Daniel Rosenfeld of Hebrew University's Earth Sciences Institute, Halfon's findings demonstrate the fact Israel is impacted by different mechanisms than those influential in the northern Mediterranean region - from Turkey to Italy - where diminishing rainfall is already clearly evident.
However, Rosenfeld emphasized that in northeastern Israel in the Lake Kinneret basin area there is a multi-year downward trend in rainfall. "The annual amount of water reaching Lake Kinneret today has dropped by 100 million cubic meters compared to quantities recorded 40 years ago," Rosenfeld said. "There are a number of explanations for this, and one of them is climate change."