August Update

This pair of images provides a glimpse of how the Northern Ice Field has changed over the past ten months. Last week the surface was relatively flat (left), and ~70 cm lower than when penitentes covered the glacier in October of last year (right).

October's penitentes were the result of sublimating snow from the previous wet season (i.e., masika or long rains, March-May 2010). Subsequently, little snow accumulated during either the 2010 short rains or the 2011 long rains (although there was an important event in February, see details). Less snow results in higher net radiation at the glacier surface, leading to ablation.

The right-hand image shows the AWS after repositioning the tower into the ice; note the lowest of the three enclosures, gray in color with the blue strap barely visible. Ten months later the same enclosure is well above the surface, with nearly half the tower base section exposed.

Paradoxically, the glacier surface appears relatively bright in the August image (i.e., high albedo). Two observations help account for this, and indicate why there hasn't been even more than 70 cm ablation. The first is a SPOT satellite image from 17 June (courtesy Nicolas Cullen) showing partial snow cover within the crater. This snowcover - likely to an even greater depth on the glacier - may have been residual from the long rains and/or the result of snowfall only 8 days earlier, a relatively uncommon event in June. The second observation is from the photographer of the left-hand image, Dr. Clavery Tungaraza (Faculty of Science, Sokoine University of Agriculture in Morogoro, Tanzania). In crossing the crater on 8 August, he reported walking through ~15 cm of snow showing no signs of melting, in dry, very cold weather. Again, some of this snow may have been residual, and some may have been associated with a couple small snowfall events during July. The very next day, as Clavery was desending, telemetry from the AWS indicates a multiday snowfall event began!

Nonetheless, dark old ice is just beneath the mantle of snow or superimposed ice creating the bright appearance in last week's image. In another two or three months, it is quite possible that the one-year net loss of ice from the Northern Ice Field surface may amount to a meter or more. This would make 2010-11 among the most negative years since 2000, perhaps not surprising in the context of drought impacting the Horn of Africa just to the north.

[UPDATE 9/4:  The snowfall event mentioned above continued from 9 to 15 August and resulted in net accumulation of ~5 cm. This brightened the glacier surface and temporarily suppressed ablation for a week. Net surface lowering for the month was similar to July at ~8 cm.]

Kilimanjaro Glaciers

Just over a century ago, glacier ice encircled the summit crater of Kilimanjaro, with perhaps only the inner Reusch Crater free of ice. (On the image above, the Reusch Crater is the middle, or second largest, of the three depicted. For scale, it is ~800 m in diameter.) Although their areal extent is now greatly reduced, as evident on this July 2009 image, the glaciers remain both beautiful and scientifically fascinating.

I wrote an overview of the mountain's glaciers that has just been published by Springer, as a contribution to their new Encyclopedia of Snow, Ice and Glaciers. The Kilimanjaro chapter briefly describes the history of glacier research on the mountain, and describes what makes these ice masses unique. It is available here.

Dry Season Ablation

Dry conditions continue at the summit, likely reflecting dryness on larger and longer time/space scales. Telemetry from the weather station reveals only 3-4 snowfall events since October, with the largest being that in mid-February as previously noted. One minor snowfall of a few centimeters in June served to brighten the surface slightly, enhancing reflection of solar radiation. Nonetheless, the surface lowered by ~5 cm during June and has increased this month.

Just north of the Kilimanjaro region, drought conditions are contributing to severe famine, with over 10 million people in need of humanitarian assistance. Although suffering and displacement are greatest in Somalia, large areas of Ethiopia and Kenya are struggling with food insecurity. A map posted on the Reliefweb site shows the geography of the problem as of mid-July; Kilimanjaro is just south of Kenya's southernmost Emergency Zone on the map. Another graphic from the Famine Early Warning Systems Network provides further details.

[UPDATE 8/8:  NASA's Earth Observatory website has been covering the developing drought since last autumn when rainfall was below normal, and has posted a series of SPOT and other images. There is also an overview discussion on how the tropical Pacific is involved, through La Nina teleconnections.]

Synopsis of 2010-11 wet seasons

By the first of June an extended dry season is typically underway at the summit of Kilimanjaro, one of the most reliable features of a climate with considerable interannual variability. In a regional context, this dry season follows the "long rains" (Masika) which generally encompass much of the 3-month interval March through May. A second, shorter wet season (Vuli) happens in November-December and is somewhat more variable in magnitude and timing.

This year, neither Vuli nor Masika resulted in net accumulation, which will likely result in tremendous ablation on Kilimanjaro's horizontal glacier surfaces during the next 5-6 months. Just how little accumulation was there? Well, between 1 Nov. and 1 June (encompassing both accumulation seasons), a 30 cm net lowering of the Northern Ice Field was very consistent between the two sensors (i.e., -28 and -32 cm). For the same interval of 2009-10, the surface increased by over 60 cm.

During the brief dry interval between Vuli and Masika (usually occurring during January and/or February), ablation also predominated, except for one snowfall event detailed earlier that turned out to be the largest snowfall event of either 2010-11 wet season, and the largest since the previous May.

More humid... but no accumulation for March

During March, there was no snow accumulation on the Northern Ice Field. Telemetry indicates a couple minor snowfalls which weren't recorded by both of the ultrasonic sensors, and then an event of 5-10 cm on 18 and 19 March. Nonetheless, the average net change in surface height amounted to 0.0 cm.

Atmospheric humidity increased during the month however, so accumulation during April and May is more likely. This is the typical pattern, as the long rains (Masika) get underway with passage of the ITCZ over the region (see here, for example). February is rather dry on average, relative to the prior 3 months (NDJ), with the mean vapor pressure increasing 0.2-0.3 hPa from February into March. This year, the mean relative humidity increased by 20 percent; vapor pressure data are not yet available.

new video

Here is a new video produced by Caleb Medders at NBC Learn about glacier recession in general, including some brief thoughts on Kilimanjaro.

Snow!

A 3-day snowy interval was underway at this time last week, bringing over 50 cm of snow on Tuesday to Lava Tower camp at the 4,600m level - and ending an extended dry period. This snow required some climbers to turn back, according to Simon Mtuy at Summit Expeditions, as continuing up the mountain became too difficult. We hope to post photos of the event here shortly.

At the summit, snow began accumulating on Sunday the 13th and continued into the 16th. Telemetry indicates that the event brought somewhere between ~19 and 28cm to the glaciers. Through noon today (local time) the new snow had settled and ablated by 5-10cm, over the past ~5 days.

Hopefully this snowfall brought much-needed rainfall to northern Tanzania. Perhaps the "long rains" are beginning, a bit early?

[UPDATE 3/4:  Below are a couple images as the event was beginning. The first illustrates slight accumulation around the two stations on the first day of snowfall. The lower image is a view of Birafu Camp on the second day. The heaviest snowfall came the next day, which some guides describe as the most they can recall in ~4 years. Both images courtesy of Clavery Tungaraza]