As we continue to despair over the lack of rain Amboseli when it seems to be raining all around, we scratch our heads wondering why? We have a theory...

Of course, there have been three years of bad rains throughout Kenya, but even as the below-normal rain falls here and there, the seemingly 'cursed core' of the ecosystem -- right in the heart of the elephants' range -- remains starkly dry, with only a few millimeters at the end of this 'rainy season', the so-called 'short rains'.

Short indeed: the 21 mm in November and December this year is really too little, too late, compared with a 62 mm average for the same period over the 40-odd years we have been keeping records

Cynthia and the field team have noticed for years that clouds build up on the slopes of Kilimanjaro, east over the Chyulus, and over the northern and western bushlands, but it always seems to rain in the Amboseli basin last. See the first image, a panorama taken in mid-December looking north from the edge of the Elephant Research Camp. You can see that there is almost a ring of clouds, with a cloud-free hole centred right over the basin.

We have a theory, splendidly, unverified as yet by expert opinion or measurement, but we thought we would offer it for discussion. It has to do with the Amboseli soils (recall, the name is derived from the Maa word 'empusel', meaning salty dust).

First, here's a thumbnail description of the Amboseli ecosystem (from our book currently in press; see: The Amboseli Book):

The Amboseli ecosystem is a roughly 8,000 km2 area that straddles the Kenya-Tanzania boundary, reposing at 1,100 m, as a broad basin between the northern slopes of Kilimanjaro, the late (post-Pleistocene) volcanic Chyulu Hills (2,200 m) to the east, a motley range of broken basement hills to the north and scattered granitic outcrops and earlier volcanic cones to the west and southwest, the largest of which, Oldonyo Orok, is 2,400 m. The most recent eruption of Kilimanjaro about 1.5m years ago blocked the ancient Pangani River that flowed northwest-to-southeast and thus created a closed central basin and a lake with no outlet: Lake Amboseli. Today, the lake holds water for only a few weeks after heavy rains. More commonly the lake is dry; the lacustrine silts that have accumulated over the years reflect starkly white on satellite imagery.

The key may be in the last sentence: the highly reflective white soils of the central basin. Interpreters of satellite imagery and geophysicists call the reflectance from light-coloured areas of the earth's surface, like snow and water, 'albedo'. See the Wikipedia discussion.

Have a look at the GoogleEarth view of Amboseli in the second image above. The National Park is outlined in yellow; the long diagonal line is the Tanzania-Kenya border. The white soils of the basin are quite obvious. If you de-colour the image, increase the contrast and apply a blue filtre (third image), the contrast between the albedo of the centre and the surrounding land is very clear.

Now, our pet theory is that the heat energy of the focused albedo of the central basin creates a vertical column of high pressure that 'pushes' rain clouds outwards and away from the centre. Thus the clouds may start to do their precip business in the surrounding areas, but the centre remains splendidly dry and cloud free.

Gradually, as the rainy season sun delivers less net energy and the odd shower slips into the basin, darkening the soils slightly and encouraging the beginnings of grass re-growth, the albedo effect ebbs, and the clouds close in.

So there it is. If there are any geophysicists or micro-climatologists out there who have other ideas, or who would like to field a research team to find out what's really going on, we'd love to hear from you.