Research notes increase in frequency of especially hot nights in past 30 years, as well as a decline in number of days with precipitation of 10 millimeters or more
Zafrir Rinat | Jun. 25, 2019 | 9:09 PM

A new study points at a warming trend in Israel over the past 70 years, which has strengthened in the past three decades. At the same timeת a trend toward a decline in the amount of precipitation, mainly after a small number of very powerful climate events, was also noted.

The findings are based on an analysis of extreme weather events measured in 30 stations throughout the country for measuring temperature, and 60 for measuring rain. It was found that in one of the stations, which operates in Kibbutz Ein HaHoresh in central Israel, the rate of temperature increase is not 0.1 degrees centigrade per decade – according to a previous estimate – but 0.26 degrees.

It was also found that the average minimum temperature increased each decade at a rate of 0.24 degrees, while the average maximum temperature increased at a rate of 0.19 degrees per decade. The analysis of the findings took into account various factors that could have affected the accuracy of the measurements, including a change in the surroundings of the weather stations, equipment or location, among other things.

The study also demonstrates that in the past three decades there has been a clear increase in “periods of high temperatures” – at least six consecutive days on which the maximum temperature is in the range of the highest temperatures for that year. Their number increased by eight days a decade in the past three decades, as compared to years between 1961 and 1990.

There was also a seven percent increase in the frequency of especially hot nights, and a decline in the number of especially cold ones. In the past three decades, with the exception of five years, the winter was hotter that the multi-year average between 1961 and 1990.

According to Yitzhak Yosef, a researcher in the climate division of the Israel Meteorological Service who led the study, the increase in the number of nights defined as especially hot created a heat index that also has a significant effect on energy consumption and the development of agricultural crops.

Yosef conducted the study as part of his doctoral dissertation at Tel Aviv University and presented the findings last week at the annual conference of the Israeli Society for Ecology and Environmental Sciences which was held at the Porter School of Environmental Studies at TAU. The findings were also published in the International Journal of Climatology.

The study also indicated a decline in the number of days with precipitation of 10 millimeters or more. Each decade saw a decline of a day in the overall number. When we examine the changes during the period of the study from a spatial point of view, the conclusion is that in recent decades the heat index increased at night in Israel’s coastal region, while in the mountainous regions it increased mainly at noontime.

The study did not directly address climate changes, and focused on a more accurate analysis of the findings from the measuring stations. At the conference in which Yosef took part, another study conducted by Assaf Hochman of TAU, indicated an anticipated trend of a decline of up to 30 percent in the frequency of Cypriote low pressure systems – a weather system that creates most of Israel’s precipitation. Hochman used a model of various weather forecasts in Israel for the coming century, based on several scenarios of climate change.