Aircraft Measurements of Surface Albedo in Relation to Climatic Changes in Southern Israel

Summary Recent studies imply that significant climatic changes over the central and southern coastal plain in Israel may be due to changes in land usage, which have taken place since the National Water Carrier operation in the early 1960’s. Such changes are reflected in the spatial distribution of the surface albedo pattern, obviously resulting in changes in the surface radiation balance and, subsequently, modifying the surface heat fluxes and the stability conditions of the Planetary Boundary Layer (PBL). An Eppley PSP Pyranometer facing downward was mounted on a small Cessna aircraft and flown along the coastal plain from Tel Aviv to the northern Negev south of Beer Sheva, at an altitude of approximately 500 feet, measuring surface reflection. The incoming solar radiation was measured simultaneously, at several surface radiation stations of the Israel Meteorological Service, along the flight path. The results show large differences in surface reflection distributions, between the cultivated areas in southern Israel (as low as 0.15), and the adjacent arid regions (with values of up to 0.35). Historical albedo maps were reconstructed according to land utilization maps of the 1930’s and the 1960’s. A comparison between recent albedo map and the reconstructed maps, indicates temporal changes in the surface albedo pattern during the last decades. Received January 15, 1998 Revised June 23, 1998     

The distribution of snow in Israel

The area researched is characterized by changes in the weather according to fluctuations in the world pressure belts throughout the year. The temperature climate in this region is typified in winter by changes in the pressure system from cyclonic to anti-cyclonic conditions in spells of about 5 days.When Israel is under the influence of a low pressure system, and the 500 mb surfaces are approximately 250 m lower than average, the temperatures along the vertical cross-sections are 6° – 8° C lower than average on rainy days, then snow may be expected in various sections of the country.This paper investigated the 35 years period from 1938/9 to 1971/2, concentrating on two mountain stations — Jerusalem in the centre of the country and Mt. Kena'an in the north —because of the high snow incidence and its greater regularity than other stations.The conclusions are as follows: The maximum number of days of snow (between 2/3 and 3/4 of the annual total) is noted at all stations during January and February, although there are also years in which there was snow but not during those months. Regional devision of the snowy days indicates that the number increases with altitude, and decreases from north to south.Snowfall in regions which have lower incidence is less stable and given to greater fluctuations. There was no indication of periodity of the number of days of snow per season, nor did it appear that a very snowy year followed a dry one.Investigation of the lenght of the snowy and the number of days of snowfall does not indicate any connection between them, and there may well be a long season with few days of snow, or a short one with relatively many snowy days.Comparison between the shorter period of readings — from 1938/9 till 1971/2 — and the longer one — from 1860/1 till 1971/2 (111 years) — at the Jerusalem station shows the same trends, which reinforce the conclusions presented above.     

Long-term change in October rainfall patterns in southern Israel

Summary A comprehensive study of long-term changes in October rainfall patterns in southern Israel, a semi-arid fringe zone between the Mediterranean coastal plain and the Negev Desert, was carried out. It was earlier postulated that the observed positive trend in October rainfall amounts may result from land-use changes in the area following the installation of the National Water Carrier (NWC) in the early 1960s. The purpose of the present study is to delineate the anticipated local effects, as well as their spatial extent, in order to investigate the possibility of climatic change over a larger synoptic scale.In the study region, a total number of 51 rainfall stations with long-term records up to 55 years, were analyzed, along with six control stations in other parts of the country. All stations were analyzed for trends in early seasonal rainfall, spatial variability during the two reference periods before and after the 60s, and for the ratio between rain per day (RPD) and number of rain days (NRD) during the two periods.The results of the analyses point to a well defined localized climatic change in October rainfall patterns within the study area, that is traceable to intensive and extensive land-use changes following the installation of the NWC.With 5 Figures     

Lake Kinneret (Sea of Galilee) and its exceptional wind system

From 1973–1976, research was performed around the Sea of Galilee, aimed at examining the wind regime in the area and whether the area develops a land-sea breeze despite its particular topographical location.

The main conclusions were:
1. During the summer mornings a lake breeze develops, blowing towards the shores of the lake. It ceases at the peak of its development when a westerly wind, originating in the development of a breeze along the Israeli Mediterranean coast, plunges towards the lake.
2. Late at night, a wind flow develops from the land towards the lake, which combines with the katabatic winds that blow along the steep slopes surrounding the Kinneret.
3. The stations at the upper level, at a height of 400–500 m above the Kinneret, are not affected by the lake breeze during the day or by the land breeze at night.
4. In winter, the Kinneret lake breeze is almost as developed as in summer, because the westerly winds, originating in the Mediterranean sea breeze which hardly develops in this season, do not plunge into the Kinneret.

     

Planning and climate — The case of Di-Zahav

Climate is one of the important factors which must be taken into consideration in all levels of planning. Despite its importance many planners are still unaware of it. An excellent example of such a situation is the case of Di-Zahav, a new settlement located about 130km south of Elat, on the alluvial fan of Wadi Dahab, which flows to the Gulf of Elat.In addition to its extreme hot and arid climate, the region suffers from very strong winds blowing throughout the year from the northerly direction. Heavy rainfall on the 19—20 February 1975 caused a considerable flood in the Wadi Dahab. Because of a mistake in the construction of the road leading to Di-Zahav, the settlement was inundated. After the water dried up, the strong north winds blew sand and dust into the village and dunes accumulated between the buildings. The strong winds are also a negative factor in human comfort and are an obstacle in the development of tourism which is the economic basis of Di-Zahav. Therefore, it seems that the location of the settlement on the southern part of the alluvial fan instead of on the north-eastern edge was a mistake. Also the detailed plan did not take into consideration the negative effects of the climate. It was therefore necessary to plan and carry out a peripheral and internal protection system consisting of planted and artificial windbreaks. It was also suggested to carry out some modifications in the buildings in order to prevent the strong winds blowing into them.     

Climatological aspects in locating settlements in arid regionsKlimatologische aspekte bei der standortwahl für neue siedlungen in ariden regionenAspects climatologiques dans l'emplacement de villages dans des régions arides

In arid and semi-arid regions it is important to pay attention to climatic factors in locating and planning new settlements. Physical factors such as large differences in elevation over short distances, proximity to a large lake or the combination of the two factors, cause improvement of the climate.The central Jordan Valley and the Dead Sea could be a suitable area for proving these assumptions. A topo-climatological research has been performed in this region to help the planners in finding the best locations for new settlements. By using a “discomfort index”, which is based on temperature and humidity, the influence of the above mentioned physical factors on local climate modification has been verified. Also, its importance in the improvement of the location of new settlements has been shown.     

Easterly Wind Storms over Israel

Summary Continental wind storms are common along the Mediterranean coast. Along the northern coast they are mostly cold, similar to the Bora or the Mistral, and along the southern coast they are mostly warm, e.g., the Ghibli or the Shirocco. At the eastern Mediterranean basin and the Levant region, these storms are intermittently warm and cold during the same season and often even during the same event. Quasi-stationary systems, as well as moving disturbances, are the cause of such wind storms. Accordingly, the resulting weather conditions may be extremely converse due to the characteristics of the advected airmass. Specific regions in Israel, sensitive to easterly storms, are influenced by these wind storms for about 10% of the year (e.g., the westerly slopes of the mountains and valleys with west-east orientation). The frequency, however, of widespread storms covering the entire region is only approximately 1.4% of the entire year. These wind storms are therefore classified in the present study according to their climatological and synoptic characteristics; indicating that the dominant synoptic situation is the Red-Sea trough and the warm advections. These storms appear only from October-May and are most frequent during the cold season. The diurnal course is characterized by a strengthening in the morning hours and a weakening at noon and in the afternoon hours, due to the opposing effect of the westerly sea breeze, suppressing the easterly winds and the effect of katabatic winds. Nevertheless, synoptic conditions may contribute to this tendency as well. Accordingly, a significant increase in the frequencies of easterly storms, in relation to distance from the seashore has been identified. Although most of the stormy days are with westerly winds, the easterly wind storms has vast environmental implications, creating damage especially to agriculture and occasionally also to property and life; coastal flooding, potential air pollution, intensifying of forest fires and occasionally dust and sand storms. Received September 9, 1996 Revised March 6, 1997