MODIS image of the central Libyan Desert
29th August, 2005 (Source: NASA)
Click on image for larger version
Jebel Uweinat

Aftermath of the rains
of 29th August 2005




This page has been updated
with our observations of October 2006,

March 2007, and October 2007,
including evidence for a small
localised rainfall in September 2006


I owe many thanks to Alessandro Menardi-Noguera and Norbert Brügge, who provided information on their observations in the western part of Uweinat, and allowed their photos to be reproduced here. Alessandro also spent many hours pouring over MODIS and Eumetsat data to pinpoint exactly the date of the rains.

I am also indebted to Nadia and her lovely website, www.sahara-nature.com, that made the identification of several of the never before seen species possible.

When we arrived to Karkur Talh on the afternoon of the 17th October, 2005, everything appeared normal, that is dry and lifeless as usual. The following morning we drove from camp to the rock island containing the first rock art sites in the main valley, and while going around, I noticed something green on the far side of the valley. On approaching, we could see several green shoots, then as we reached the little dip marking the watercourse, we were amazed to see a green carpet covering the bottom of the wadi. The fresh vegetation was stricly limited to the bed of the watercourse (the transition zone was less than one metre wide), and we soon saw, that the water flow ended close to our position at the confluence of the main and south branches. Very clearly the source of the water was rain at higher altitudes of the mountain, and we chanced upon the fresh vegetation very near to the end of the flow.

   
Fresh growth in the lower section of Karkur Talh (18th October, 2005). New vegetation is limited to the watercourse meandering accross the wadi bed, and ends where the runoff stopped.
   
Fresh growth is limited to the areas touched by flowing water. Areas left unmoistened even a few centimetres away remain barren.

The majority of the fresh growth was Tribulus pentandrus, creating a thick carpet of green sprinkled with bright yellow flowers. Tribulus dominated practically all of the area moistened by water, with only a few intermingled other species. Along the border of the flow, there was a thin zone of about half metre, where wrinkled Tribulus shoots attested to the marginal conditions, insufficient to complete the full life cycle of the plant. Closer to the center, all shoots were flowering. It was noted later, that the flowers closed as sunlight faded, and opened again the following morning.

   
   
Growth of Tribulus pentandrus near the end of the water flow in Karkur Talh.

The second most common species, Cassia italica grew intermingled with Tribulus, but in much fewer numbers. The larger individuals all bore fruit at the time of observation, and there were already dried pods lying on the ground under some of the plants. Interestingly, there were many vigorous young shoots, especially along the border of the green zone, where the Tribulus shoots were all withered.

     
Cassia italica intermingled with the more abundant Tribulus pentandrus near the end of the water flow in Karkur Talh.

All the tufts of the normally dry Panicum turgidum in the watercourse supported abundant fresh growth, while those unaffected by water remained dry, even in the close vicinity.

     
Green and flowering tufts of Panicum turgidum in the bed of the watercourse in Karkur Talh,
in the area dominated by Tribulus pentandrus and Cassia italica.

Towards the end of the watercourse, numerous Citrullus colocynthis plants were seen, some already bearing full sized fruit. This helped time the rain event to at least five to six weeks prior to our arrival. Near the edge of the waterflow, Citrullus became as abundant as Tribulus, spread out among tufts of Panicum.

   
   
Citrullus colocynthis in sandy wadi bed alongside Tribulus pentandrus and
Panicum turgidum at the end of the water flow, Karkur Talh.

Along the edge of the waterflow, several eaxamples of another species was noted. On first look, they appeared similar to the withered and underdeveloped Tribulus in the same area. However close observation revealed small white flowers and clusters of small air filled pods. The species was subsequently identified as Astragalus vogelii.

   
Astragalus vogelii along the edge of the moistened area in middle Karkur Talh.

In the same general area near the end of the waterflow, single individuals of two further species were noted, Farsetia ramosissima and Zygophyllum simplex. Both specimens were unique examples, neither species were noted elsewhere.

     
Farsetia ramosissima in the bed of the watercourse in Karkur Talh, in the area dominated by Tribulus pentandrus.
  Zygophyllum simplex in the bed of the watercourse in Karkur Talh, in the area dominated by Tribulus pentandrus.

A young Acacia raddiana was also noted in the area. It is unlikely, that in six weeks the germination - growth cycle would have produced such a large plant, more likely the growth of an already existing shoot was accelerated by the water. In the vicinity of the young Acacia an Indigofera sessiliflora was noted, which appeared sporadically in the whole area. A single Aerva persica was also noted near the end of the water flow, it is unclear whether it was fresh growth, or a rejuvenated existing plant. A little further upstream another Aerva was noted, this time clearly a fresh shoot that grew following the rains.

     
Young Acacia raddiana in the watercourse, Karkur Talh (note unidentified species in background).
  Indigofera sessiliflora in the bed of the watercourse in Karkur Talh

  Aerva persica near the end of the water flow, Karkur Talh

  Young Aerva persica among Tribulus terrestris in Karkur Talh

Walking a short way upstream from the end of the water flow, a large fleshy leaved plant was seen, sporting small purple cruciform flowers on long stems. This was the first example of Schouwia thebaica, which progressively became more abundant as one moved upstream. Schouwia was the largest plant noted among the fresh growth.

     
Schouwia thebaica in the bed of the watercourse in Karkur Talh, among Tribulus pentandrus and tufts of Panicum turgidum

Following the watercourse upstream, the composition of the vegetation remained unchanged. Tribulus pentandrus continued to be the dominant species among the rejuvenated Panicum turgidum tufts, intermingled with Cassia italica and a few of the already noted species. The first new species was noted about one kilometre upstream, in the centre of the Acacia raddiana grove occupying the upper and central area of the middle course of Karkur Talh (prior to the confluence of the two main western branches). This new species was a fleshy leaved, pale green plant with cruciform white flowers. It took some time to positively identify it as Morettia philaeana (first it was misidentified as Malcolmia africana, a species not recorded by others at Jebel Uweinat).

     
Tribulus pentandrus among tufts of Panicum turgidum in the central part of Karkur Talh
  Morettia philaeana intermingled with Tribulus pentandrus in the central part of Karkur Talh

There were many insects flying in the air surrounding the flowers, but the only new species noted on account of the rain was a large beetle, flying through the air with a characteristic rattle. The species was identified as Julodis fimbriata, a member of the jewel beetles family (Julodinae). It begins its life cyce as a larva burrowing inside a host plant, Acacia raddiana, and emerges to mate and reproduce only fllowing rains.

   
Julodis fimbriata in middle Karkur Talh

Throughout the green area, the surface was completely dry, and the sand continued to be dry as far as one could excavate by hand. In the middle section, the centre of the watercourse was investigated to a greater depth using a shovel. The sand remained dry up to a depth of approximately 80 centimetres, when moisture first appeared. At a depth of one metre, the sand was distinctly wet, however no standing water collected at the bottom of the hole up to 1.2 metres.

Further upstream, at the densest part of the Acacia grove, the green area expanded to a width of about 20-50 metres, and the ground was covered with a thick green carpet of Tribulus pentandrus.

   
Tribulus pentandrus forming a continuous green carpet in the Acacia raddiana grove in Karkur Talh

Reaching the confluence of the two main western branches, it became clear that the source of the water was the northern of the branches. The south branch, draining the Hassanein Plateau, was completely dry as usual (and subsequently confirmed to be so in the upper reaches as well). (Note: In October 2006 we have found some evidence suggesting that there may have been some smaller rain on the slopes of the Hassanein plateau)

The vegetation in the northern branch became densest near the end of the drivable section, where a series of basins must have held water for a considerable time. There was a lush growth of Tribulus pentandrus, however no longer dominant, mixed with Schouwia thebaica, Morettia philaeana, Citrullus colocynthis, and abundant fresh growth of Aerva persica.

     
     
     
Vigorous growth in dried up pools at the beginning of the rocky upper section of Karkur Talh

In the dried silt of the shallow pools, a fresh Acacia raddiana shoot was noted, that clearly germinated following the rains. In the same area a new species was noted, Fagonia indica.

 
Young Acacia raddiana shoot in upper Karkur Talh

  Fagonia indica in upper Karkur Talh

The next morning (19th October) a side excursion was made into Karkur Murr, starting along the footpath from Karkur Talh. The south western branch was dry, as noted the day before, as was the beginning of the small side wadi that leads to the start of the trail. However close to the beginning of the ascent, a dry pool was seen in the side wadi bed, that supported some fresh growth. Apparently there was some very localised rainfall, and the runoff collected in this pool which enabled some plants to take hold. The majority of the shoots were young Aerva persica, plus a single shoot of Astragalus vogelii, flowering Convolvulus prostratus, and a strange ground hugging plant that was subsequiently identified as Euphorbia granulata. No further live vegetation was seen until reaching Karkur Murr, which showed it's usual dry state, with green vegetation limited to the vicinity of the springs.

   
   
Young Aerva persica, Astragalus vogelii, Convolvulus prostratus and Euphorbia granulata in dry pool in side wadi of south western Karkur Talh

The following morning (20th October) an excursion was made to the upper north western branch of Karkur Talh, to the rock art sites discovered by the Belgian expedition in 1968. The vegetation between the area seen two days earlier and the rock art sites remained essentially the same, dominated by a mixture of five species, Tribulus pentandrus, Schouwia thebaica, Morettia philaeana, Citrullus colocynthis, and Aerva persica. A few Fagonia indica were also noted among the rocks.

     
     
Tribulus, Schouwia, Morettia, Citrullus and Aerva vegetation in the upper section of Karkur Talh

In a few spots among the rocks a short grass species, Stipagrostis plumosa was noted. It was short (max. 20cm height) and slender, with fully formed garlands. In the same area, a second smaller grass species, Aristida mutabilis, was noted.

 
Stipagrostis plumosa in upper Karkur Talh

  Aristida mutabilis in upper Karkur Talh

Near the rock art sites a few individuals of two plants were noted that were not seen in the lower courses of the valley. One, bright green with little yellow flowers, was identified as Cleome crysantha. The second, spread out and closely hugging the ground, was identified as Boerhavia coccinea. Cleome was only seen in this location.

     
Cluster of Cleome crysantha in upper Karkur Talh

  Boerhavia coccinea in upper Karkur Talh
(note unidentified (2) species in bottm left)

Near the Boerhavia specimen, two Indigofera species were noted. Indigofera sessiliflora was already familiar from near the end of the runoff, however Indigofera disjuncta was not noted elsewhere. It was a bright green plant with shiny leaves, and clusters of long pods radiating from the stems where the leaves joined.

     
Cluster of Indigofera sessiliflora in upper Karkur Talh

  Indigofera disjuncta in upper Karkur Talh

On our return walk, instead of following the main valley, we set out to explore the area to the north of Karkur Talh. We noted with some surprise, that some of the shallow wadi beds on the plateau above the main valley showed signs of recent water flow, however there was no vegetation whatsoever. It appears that there was a small localised downpour in the area of the conspicious flat topped hill to the north of Karkur Talh, however insufficient to start any new growth. In the largest of the northern tributaries we did chance upon two green plants, a pair of Euphorbia granulata, in an area that was otherwise completely void of any fresh vegetation. (This is the same valley that contains further downstream the largest known Maerua crassifolia individual, which showed it's usual state.)

 
Euphorbia granulata in a nothern tributary of Karkur Talh, which showed signs of recent running water, but supported no other fresh vegetation

On the late afternoon of the same day (20th October) we set out to explore Wadi Handal, a small wadi a few kilometres to the west of the mouth of Karkur Talh, not explored on any of the previous visits. It was a great surprise to see upon entering the wadi, that it was lush green, with denser vegetation than that noted in Karkur Talh. As the Wadi Handal basin is fairly small, and lies to the north of Karkur Talh, this suggested that the source of the water was not rain on the high plateaus of Uweinat, but rainfall to the north of the sandstone plateaus, which flowed partially north into Wadi Handal, and south into the north western branch of Karkur Talh. (As time was short, the wadi was re-visited for a longer period on the 23rd October. The following description is a combination of both visits.)

   
   
Entrance of Wadi handal (Jebel Uweinat), where Cirullus colocynthis (Handal) is the dominant vegetation, alongside Tribulus pentandrus

In the lower section of Wadi Handal there is a broad flat basin that is blocked by a large dune at its end, containing a small grove of Acacia. This basin was completely green, supporting a mix of Citrullus colocynthis (Handal, after which the wadi was named by the Belgian theam on account of it's abundance), and Tribulus pentandrus.

   
   
Entrance of Wadi handal (Jebel Uweinat), where Cirullus colocynthis (Handal) is the dominant vegetation, alongside Tribulus pentandrus

The smaller Acacia trees were densely packed with mating Julodis fimbriata. These large beetles appeared to be much more abundant here in Wadi handal than in Karkur Talh, and all the smaller acacias were filled with them in both the lower and upper reaches of the wadi.

     
Julodis fimbriata on Acacia in Wadi Handal

On the sandy lower course of Wadi Handal, aside the dominant Citrullus and Tribulus, only a few other species were noted. A few individuals of fresh growth Crotalaria thebaica (in Karkur Talh no fresh growth was noted), Cassia italica (much fewer than in middle Karkur Talh), Fagonia indica (few scattered individuals), and Boerhavia coccinea (single specimen).

     
Cirullus colocynthis, Crotalaria thebaica, Fagonia indica and Boerhavia coccinea in the sandy bed of lower Wadi Handal.

About two kilometres from it's mouth the wadi narrows, and becomes a rocky winding gorge. About two kilometrs upstream, we found a small rock pool that was in almost perpetual shadow, still containing water.

   
   
The narrow rocky middle section of Wadi Handal, with the guelta (rock pool) near it's upper end

The vegetation in the rocky gorge, became thinner but essentially the same species, dominated by Citrullus and Tribulus, with sporadic Fagonia indica, Crotalaria thebaica and Cassia italica.

   
Fagonia indica and Crotalaria thebaica in middle Wadi Handal.

Near the middle of the gorge, a large flowering specimen of Pulicaria incisa was seen. In the vicinity there were many young shoots just emerging from the dried-out bed of a large basin.

     
Single flowering and numerous sprouting Pulicaria incisa in middle Wadi Handal.

Above the rock pool, the wadi flattened out, and eventually became a shallow rocky ditch in the surrounding plateau. The species remained the same as noted in the lower course, with the addition of Morettia philaeana and Schouwia thebaica. Boerhavia coccinea became noticeably more common, including several very large specimens. Cassia italica also became more frequent, and a few individuals of Indigofera sessiliflora were noted.

   
The upper section of Wadi Handal


     
Pulicaria incisa intermingled with Morettia philaeana, Boerhavia coccinea, Cassia italica, and Indigofera sessiliflora in upper Wadi Handal.

On the 22nd October our party went to the southern side of Jebel Uweinat, to visit the rock art sites of Wadi wahesh. No further fresh vegetation was seen anywhere along the eastern periphery of the mountain, and the bed of Karkur Murr out on the southern plain was as dry as the upper reaches. Wadi Wahesh was similarly dry, in both the lower and upper reaches. While half of our party explored upper Wadi Wahesh, the other half visited some sites further west. On returning, they have reported that the bed of the first major wadi to the west of Wadi Wahesh was full of green vegetation for a considerable distance out on the plain.

Returning from Uweinat, contact was made with Alessandro Menardi Noguera and Norbert Brügge, both of whom have been to western Uweinat on separate trips. In October 2005, Norbert reported seeing fresh green vegetation in the upper-middle reaches of Karkur Idriss, and in the middle section of Karkur Ibrahim. In both cases the fresh vegetation identifiable on Norbert's photos (taken 11th October) is Tribulus pentandrus, clearly indicating the presence of rain runoff in those sections of the wadis.

     
Middle Karkur Idriss
(Photos by Norbert Brügge)
  Middle Karkur Ibrahim
(Photos by Norbert Brügge)

In the period 25-28 April 2006, Alessandro Menardi noguera and companions visited the Emmeri plateau and other parts of western Uweinat. There was ample green vegetation in the valleys on the Emmeri plateau, apparently the remnants of rain induced growth from the previous year. The noted species were Cleome crysantha, Aerva persica, Cassia italica, Fagonia indica, Tribulus pentandrus and Schouwia thebaica, all species noted in eastern Uweinat the previous October. Though all were flowering, some (especially Schouwia) were clearly reaching the end of their life cycle.

   
   
   
Cleome crysantha, Aerva persica, Cassia italica, Fagonia indica, Tribulus pentandrus and Schouwia thebaica (note semi-dried state) on the Emmeri highland (Photos by Alessandro Menardi Noguera)

In a small ravine along the western side of the mountain, Alessandro and party noted a large cluster of Citrullus colocynthis growing from a basin among the granite boulders. The plants leaves were still green, however all the colocynths were dry.

Citrullus colocynthys among granite boulders,
western Uweinat
(Photo by Alessandro Menardi Noguera)

Browsing through MODIS satelite images provided by NASA, the only date when the cloud cover was sufficient to provide the rain of this magnitude was on the 29th of August, 2005. This matches well with our own assessment in October, that the vegetation was six to eight weeks old.

In October, 2006 we have re-visited Jebel Uweinat, and quite unexpectedly have found that much of the 2005 growth was still green, and there was plenty of new vegetation that has sprung up following our October, 2005 visit.

At the end of the runoff of the 2005 rains, the tufts of Panicum turgidum were green and flowering, practically in the same state as the year before. They were surrounded by green, flowering and fruit bearing Citrullus colocynthis, covering a much larger area than a year before. However the green carpet of Tribulus pentandrus and Cassia italica as well as the other rarer species were all gone, shrivelled and dried up.

     
     
Karkur Talh, October 2006, near the end of the 2005 rain runoff.
Green tufts of Panicum turgidum and flowering and fruit bearing Citrullus colocynthis.

A single other green plant was noted in the area, a Brassicaceae that was first taken to be a new species as it was not seen before. However it was subsequently identified as Morettia philaeana, but in a form very different from the observations of October 2005 further upstream. Instead of the characteristic large serrated leaves of the fresh growth, the leaves on this plant were tiny and very closely spaced, yet it was still bearing the small white cruciform flowers.

     
A solitary green Morettia philaeana in Karkur Talh, October 2006, near the end of the 2005 rain runoff.

One previously unseen species was noted in this area, a cluster of the parasitic Cistanche phelypaea that grew on an Aerva persica host plant. Both the Cistanche and the host plant were completely dry, however the host was observed in a fresh green state a year earlier.

     
A cluster of Cistanche phelypaea in Karkur Talh, October 2006 (on Aerva persica host plant)
  The host plant in October, 2005

It was interesting to observe that the water has clearly percolated underground further downstream in the elapsed one year. The tufts of Panicum turgidum that in October 2005 were only green up to the end of the runoff were now showing sporadic fresh growth up to one kilometre further downstream, and the cluster of Crotalaria thebaica that were mostly dry with a few green offshoots were now all green, supporing vigorous new growth.

   
Green Panicum turgidum and Crotalaria thebaica in lower Karkur Talh, October 2006
(observed to be dry in October, 2005)

The south western branch of Karkur Talh showed no sign of any recent rain, however there was a noticeable change in the vegetation. The tufts of Panicum turgidum all had a tinge of green, with a little new growth in their centre. In the upper courses we have found several grazed tufts of fresh growth, one supporting flowers, something only seen before near the springs of Karkur Murr or in the watercourse of the 2005 rain runoff. There were several other fresh plants, including a conspicious Pergularia tomentosa that was definitely not there a year before, several new Aerva persica, and in the upper courses a single Cleome crysantha which hitherto has only been associated with rain runoff. All the signs indicate that there may have been some small local rain on the slopes of the Hassanein plateau (supported by finding the trace of raindrops in dust and sand) that did not produce a surface runoff, but the water percolated along the wadi bed through time. This was probably associated with the other 2005 rain events, as all observed new growth was in a similar state as the ones in the north western branch of Karkur Talh which carried the main runoff.

     
South west branch of Karkur Talh, October 2006. On first appearance completely dry, but a close look reveals some fresh growth.

     
Post october, 2005 growth of Pergularia tomentosa, Aerva persica and a single Cleome crysantha in the middle course of the south west branch of Karkur Talh (October 2006).

   
Green and grazed tufts of Panicum turgidum in the upper reaches of the south western branch of Karkur Talh (October 2006).

As we explored the upper reaches of the main (North western) branch of Karkur Talh, we encountered more surviving vegetation from the year before. Practically all the more abundant species were noted in a green condition, however their proportions were very different. Only a few individuals of Tribulus pentandrus and Cassia italica were noted, all in areas where the growth was most vigorous in the previous year, and probably some lingering moisture remained underground. Morettia philaeana was abundant (in it's arid conditions form already noted in the lower valley) in the middle and upper sections of the valley, together with Aerva persica. The Citrullus colocynthis plants that were noted a year before were mostly green and bearing fresh fruit, and even a few new shoots were observed in the middle section of the valley, however the species was noted to be completely absent from the upper section. A couple of Schouwia thebaica were noted with a few small green leaves and flowers, though the majority of the noted examples of the species were completely dry.

   
   
Remnant vegetation in the middle section of the north west (main) branch of Karkur Talh, October 2006. Tribulus pentandrus (the only flowering specimen seen), Cassia italica (one of a handful examples), Morettia philaeana (increasingly abundant going upstream), Aerva persica (common throughout), Schouwia thebaica (one of a few still green examples) and Citrullus colocynthis (young shoot, several older green and fruit bearing plants noted).

Passing the furthest upstream point visited the year before (the rock art sites discovered by the 1968 Belgian expedition) two species which were only noted sporadically in 2005, Cleome crysantha and Fagonia indica became very common, gradually becoming the dominant vegetation together with Morettia philaeana and Aerva persica.

     
     
Remnant vegetation in the upper section of the north west (main) branch of Karkur Talh, October 2006. Dominant species are Cleome crysantha, Fagonia indica, Aerva persica and in lesser numbers Morettia philaeana.

   
   
Cluster of vigorous growth of all four dominant species around large boulders, upper section of the north west (main) branch of Karkur Talh, October 2006.

   
Remnant vegetation in a dry mudpan in the upper section of the north west (main) branch of Karkur Talh, October 2006. Predominantly Fagonia indica and Cleome crysantha, with a few Morettia philaeana, Cassia italica and a single Tribulus pentandrus.

Aside the four dominant species, only sporadic other plants were seen in the upper section of the valley. A couple of mature Pulicaria incisa were noted, which species was not observed in Karkur Talh a year before, and which was at the early stages of it's life cycle in Wadi Handal (however Karkur Talh was not explored in 2006 up to the point where the Pulicaria were noted). A single Boerhavia coccinea was observed, as well as a young Cleome droserifolia that probably sprung up following the rains of a year ago. Some tufts of heavily grazed green Panicum turgidum were also seen, much in the same state as in the south western branch unaffected by the rains.

     
Remnant vegetation in the upper section of the north west (main) branch of Karkur Talh, October 2006.
Pulicaria incisa, Boerhavia coccinea, Cleome droserifolia and heavily grazed Panicum turgidum.

Reaching the fork of the two main branches of the main north western valley, it became evident that both contributed to the 2005 runoff. The same Fagonia - Cleome - Aerva - Morettia vegetation continued upstream in both branches, in essentially the same state. This enables a more precise localisation of the area of rainfall in 2005, likely to have happened along the continuous western edge of the high sandstone plateaus making up the high mass of the mountain.

Confluence of the two main branches of north western Karkur Talh (October 2006). Remnant vegetation continues upstream in both valleys.

Approximately one kilometre upstream from the fork in the right (northern) branch, we encountered several patches of very fresh growth Morettia philaeana, not in the arid conditions phase, but as fresh as a year before. In the same area, several Euphorbia granulata were observed, some in the very young phase. A couple of vigorous, fresh looking Boerhavia coccinea and Aerva persica were also noted, as well as Indigofera sessiliflora and a single Stipagrostis plumosa. All the plants appeared as young and fresh as those observed one year ago, it seemed incongruous that such growth could have been spurred by the rainfall of 2005. However the patches of fresh growth were separated by longer stretches of clearly remnant vegetation, and there was no conclusive evidence for recent moisture.

     
     
Fresh growth in the upper section of the north west (main) branch of Karkur Talh, October 2006.
Pulicaria incisa, Boerhavia coccinea, Cleome droserifolia and heavily grazed Panicum turgidum.

A few hundred metres upstream further fresh growth Morettia philaeana was encountered, covering the floor and perimeter of a dried shallow basin. This time the evidence was overwhelming that the basin was wet recently, and sure enough a few metres on we found a deep basin in the smooth bedrock of the valley floor, still filled with water. It must have rained sometime in late September 2006, as the plants were generally much smaller than those observed a year ago (when the rain event was dated to late August). The MODIS satelite images (NASA) were less helpful this time, there were several cloudy days in September, and any one of them could have produced the small local rain.

   
   
Fresh Morettia philaeana and the rock pool above in the upper reaches of the north western branch of Karkur Talh (October 2006).

It was clear that any surface runoff did not reach more than fifty metres downstream from the pool, as fresh growth ceased beyond that point. Probably the patches of new growth were due to some of the runoff traveling further underground among the rocks and gravel making up the wadi bed, and emerged at some points spurring growth. Above the pool, the wadi bed was smooth bedrock with occasionally a thin lazer of gravel and silt, where fresh growth was continuous. Morettia philaeana was the most abundant, mostly in the young shoot stage, but also several young Cleome crysantha and Fagonia indica, essentially the same as the remnant vegetation with which the new one was intermingled. In addition, single individuals of Euphorbia granulata, Indigofera sessiliflora, Indigofera disjuncta, Crotalaria thebaica and Pulicaria incisa were noted above the pool, surrounded by earlier mature vegetation.

   
   
Fresh growth above pool, predominantly Morettia philaeana with Fagonia indica, Cleome crysantha and single individuals of Euphorbia granulata, Indigofera sessiliflora and Pulicaria incisa.
Upper north western branch of Karkur Talh (October 2006).

   
Fresh growth Indigofera disjuncta and Crotalaria thebaica beside a remnant growth Cleome crysantha in upper north western branch of Karkur Talh (October 2006).

About a kilometre above the pool, a small side wadi joins the main valley from the north. We were surprised to see this ravine filled with fresh growth, it was at least a partial source for the runoff. Fresh growth continued further upstream in the main valley too, intermingled with mature remnant vegetation, however we did not have the time to investigate further upstream. The side valley provided good opportunity to observe the new vegetation without the sometimes hard to distinguish older plants. in addition to the species already noted, in the side valley we observed young Schouwia thebaica and Astragalus vogelii.

     
     
Fresh growth in the northern side valley of upper north western of Karkur Talh, October 2006. Schouwia thebaica, Euphorbia granulata, Pulicaria incisa, Morettia philaeana, Boerhavia coccinea, Astragalus vogelii and Cleome crysantha.

   
Fresh growth Cleome crysantha intermingled with Euphorbia granulata, Morettia philaeana and Astragalus vogelii in northern side valley of upper north western Karkur Talh (October 2006).

A couple of days later a visit was made to Wadi Handal, the northern valley of Uweinat adjacent to Karkur Talh, a few kilometres further west. We were astonished to see the whole lower part of the valley densely covered in green vegetation consisting of Crotalaria thebaica and Citrullus colocynthis (Handal). There was no sign of any fresh vegetation, so all observed plants have survived on the reinfall of the year before.

   
   
     
Crotalaria thebaica and Citrullus colocynthis in lower Wadi Handal (Jebel Uweinat), October 2006

Many of the Crotalaria thebaica shrubs were host to bright green spotted caterpillars, and adults of the same moth species, Utetheisa pulchella were fluttering about in large numbers. This species was only noted at Uweinat during this time and location.

     
     
Utetheisa pulchella caterpillars and adult moths on Crotalaria thebaica, Wadi Handal (Jebel Uweinat), October 2006

The basin with a grove of trees at the side of the valley, that was so lush green a year before has returned to it's normal dry state, only the hundreds dry colocinths remained.

     
Lower Wadi Handal (Jebel Uweinat), October 2006
  Same spot a year before, October 2005

The dominant vegetation in the remainder of the lower course of the wadi was Citrullus colocynthis intermingled with Crotalaria thebaica in lesser numbers, and a few thriving Cassia italica. Near the point where valley narrows to a gorge, we saw an exceptionally large Fagonia indica (about one metre accross).


     
Citrullus colocynthis, sometimes intermingled with Cassia italica in lower Wadi Handal (Jebel Uweinat), October 2006


   
Exceptionally large Fagonia indica in lower Wadi Handal (Jebel Uweinat), October 2006

In the narrow middle part of the valley the same vegetation was noted as the year before, in a more mature state and in differing proportions. Numerous Pulicaria incisa were seen in a mature but flowering state, together with Aerva persica, Cassia italica, Citrullus colocynthis, Fagonia indica, Morettia philaeana and heavily grazed Crotalaria thebaica.

     
     
Middle section of Wadi Handal (Jebel Uweinat), October 2006. Crotalaria thebaica, Cassia italica, Pulicaria incisa, Aerva persica and Morettia philaeana.

Above the gorge the wadi flattens and broadens out. A couple hundred metres beyond the point reached in October, 2005, the valley broadens further, into a large flat bottomed basin several kilometres accross. The main watercourse meanders accross the plain, supporting a grove of Acacia tortilis trees. In the basin the wadi bed was full of remnant vegetation from the year before, including still green Cassia italica, Citrullus colocynthis, Fagonia indica and Morettia philaeana.

   
   
Basin in upper Wadi Handal (Jebel Uweinat), October 2006. Grove of Acacia tortilis with remnant vegetation of 2005 rains (Cassia italica, Citrullus colocynthis and Morettia philaeana).

The rain runoff clearly came from the upper reaches of the main watercourse, placing the source of the rainfall close to the north western branch of karkur Talh. We did not have time to explore further upstream, however we did explore a little side wadi that entered the basin from the hills to the north west. Much to our surprise, after climbing a steep scree with no vegetation, we found a dissected plateau above with the small wadi filled with remnant vegetation. The green living plants were predominantly the same as in the middle section of Wadi Handal, Aerva persica and Fagonia indica, together with numerous Pulicaria incisa and a few Morettia philaeana and Crotalaria thebaica. Several species were seen in small numbers that were not noted at lower parts of the valley: Cleome crysantha, Euphorbia granulata, Boerhavia coccinea, Stipagrostis plumosa (identification uncertain), all familiar from upper Karkur Talh.

     
     
Upper northern tributary of Wadi Handal (Jebel Uweinat), October 2006.
Morettia philaeana (center foreground), Aerva persica, Pulicaria incisa, Fagonia indica and Crotalaria thebaica.


   
   
Upper northern tributary of Wadi Handal (Jebel Uweinat), October 2006.
Species unobserved in the lower sections of the valley: Cleome crysantha, Euphorbia granulata, Boerhavia coccinea and Stipagrostis plumosa (?).

Based on the observations of ourselves, Norbert & Alessandro, it is possible to create a map of the 2005 and 2006 rainfalls. The 2005 event appears to have happened on a SW - NE axis. There was some rain on the Emeri highland, attested by the vegetation that remained green till eight months later. The main rain event happened in the elevated area at the foot of the main plateau (Italia plateau), at the border of the granite and sandstone zones. The runoff drained to all directions, including both of the north western branches of Karkur Talh. This same rain moved north east, into the Wadi Handal watershed. There were two very small localised rains to the north and south of the middle main valley of Karkur Talh, however there was no rain on the Italia plateau or the Hassanein plateau. The 2006 event was very small and localised, based on the short runoff.

  • Green solid line - confirmed green vegetation, October 2005 & October 2006
  • Green dotted line - presumed but unconfirmed source of runoff
  • Yellow solid line - confirmed dry valleys, October 2005 & October 2006
  • Magenta solid line - confirmed green vegetation, April 2006
  • Magenta dotted line - presumed but unconfirmed source of runoff
  • Blue solid line - confirmed fresh vegetation, October 2006
  • Black oval areas - presumed 2005 rainfall
  • Blue oval area - presumed 2006 rainfall

In March, 2007 the middle section of the north western branch of Karkur talh was re-visited. In the upper section there were still a few surviving green plants, remnant vegetation of the 2005 rainfall. The majority were Citrullus colocynthis, some flowering and even bearing fruit, and Fagonia indica. Occasional tufts of Panicum turgidum were still green and heavily grazed, as were the solitary moted living Crotalaria thebaica and Morettia philaeana. Several Aerva persica were noted, and most surprisingly a single Cassia italica and Tribulus pentandrus. A young Heliotropium bacciferum was also noted in the area that cannot be considered remnant vegetation.


     
     
Middle north western branch of Karkur Talh (Jebel Uweinat), March 2007. Citrullus colocynthis, Crotalaria thebaica,Panicum turgidum, Aerva persica, Fagonia indica, Morettia philaeana, Cassia italica and Tribulus terrestris.


Lower and middle Karkur Talh, March 2007
video

Wadi Handal was re-visited in October 2007, in the lower section of the valley the state of vegetation was surprisingly similar to that observed a year earlier. The large Crotalaria thebaica shrubs were all green, in some cases flowering, and the numerous Citrullus colocynthis were all green, flowering and bearing fruit alongside the innumerable already two year old dry colocynths. There was no trace of any fresh vegetation, clearly all the green plants were thriving on the remnant moisture of the two year old rainfall. Further upstream, as long as the sand continued to fill the wadi bed, several green Aerva persica, Cassia italica and Fagonia indica were observed alongside the still abundant colocynths. There must be some water reservoir underneath the sand filled wadi bed that can retain moisture for such a long period. Elsewhere the two year old vegetation was completely dry.


   
   
Lower bed of Wadi Handal (Jebel Uweinat), October 2007,
with thriving Crotalaria thebaica and Colocynthis citrullus.

The vicinity and interior of the Crotalaria thebaica shrubs was host to a thriving population of insects and spiders. The black Trachyderma hispida beetles were particularly abundant, as well the Utetheisa pulchella months, noted also in abundance a year before. Several adult and a few juvenile Sparassus dufouri spiders were seen stalking inside the shrubs, as well as less numerous Vanessa cardui butterflies, several unidentified moths and a very attractive black and white spider.


   
   
Abundant insect life among green vegetation in lower bed of Wadi Handal, October 2007,
Trachyderma hispida, Utetheisa pulchella, Sparassus dufouri, Vanessa cardui and unidentified moth and spider.