Early short-rain snow

Snow conditions on Kibo have changed considerably over the past 10 days, as shown in the timelapse above. Very little seasonal snow was present on 16 October, nicely revealing the current distribution of glacier ice. Five days later the entire summit was blanketed by snow. A second-hand report from our friend Simon Mtuy indicates that the snowline on the 18th was below Kibo hut. (Simon's wonderful company is SENE).

Between the 21st and 26th, ablation of new snow appears to have dominated over additional accumulation. However, note extensive snow below the Western Breach on the 26 October image; this may have resulted from localized convection, typical on that side of the mountain. Simon was on the mountain last week, so it will be interesting to hear his observations. Low on the mountain (i.e., below 1800 m) he reports nearly non-stop rain since the beginning of October - an early beginning to the short-rains season!

Summit Snow

High elevations on Kibo received an early October dusting of snow, as shown in the Sentinel-2 image above, acquired Sunday. Until AWS data are recovered, we don't know whether this snow resulted from one event, or multiple; five days prior the summit was obscured by clouds, and it was snow-free ten days earlier.

This image reveals interesting information about ice, snow, and clouds. The brightest areas which are labeled are the remaining ice bodies. Increasing fragmentation of what was once the Southern Icefield is readily apparent. Within a few years the Heim and Decken Glacier will likely be gone, followed shortly thereafter by the Furtwängler.

Almost all other bright areas - of various sizes and shapes - are new snow (e.g., southeast of the Reusch Crater). In this scene, note how snowcover is distributed rather symmetrically on the mountain, which is typically not the case for individual snowfall events.

One large bright area to the southwest of Reusch Crater shows relatively-thick convective clouds rising above the Western Breach. Elsewhere, thin clouds appear darker and more variable in brightness, forming a annular pattern around Kibo. These clouds are low in elevation, as evidenced by the visible shadows. This annular pattern is quite common on Kibo, with clouds thickening during the day due to convection. Sometimes, the crater remains cloud-free yet encircled by clouds, if convection dominates over advection (which transports moisture laterally).

Early October snowcover usually persists for only days to weeks, with the short rains not getting underway for at least another month. Nonetheless, such events considerably influence mass balance, as snowcover greatly impacts radiative energy exchanges due, for example, to the higher reflectivity (albedo) of surfaces.

NIF shrinkage: 2015-2019

The right-hand image above depicts Kilimanjaro's Northern Icefield in mid-September (2 weeks ago). Although resolution is not ideal, minimal snowcover allows comparison with the same glacier four years earlier (July 2015). Note that the two images are not perfectly registered, so the following observations are qualitative.

Both the north and south remants of the icefield have decreased in area, especially relatively-thin portions at lower elevations. These include the northwest part of the north remnant, and the western margin of the southern part. A marginal meltwater lake is visible at the southern margin of the north portion on both images, and has been present for many years. At the eastern edge, we have observed shrinkage of several isolated blocks of ice over the years; these were present in 2017, but have now disappeared. On the south portion, thin areas and holes in the left-hand image are now ice free, including one location (southeast margin) where we have evidence that geothermal heat initiated hole formation.

The rate of glacier thinning was reduced during 2018, due to above-normal snow accumulation and the attendant increase in albedo. To illustrate, note the brighter, high-elevation portions of the glacier in the 2015 image; this is snow cover over old glacier ice.

We are hoping to visit the summit glaciers early in 2020 to measure ablation stakes, conduct GPS surveys, and photographically document changes to the glaciers since our last visit.

Regional wet-season failure

A new post on the NASA Earth Observatory website reveals the regional extent of precipitation deficit partway through the 2019 long rains. The NASA soil moisture anomaly map for April (above, from MODIS) depicts a large anomaly extending into northern Tanzania. [The Kenya-Tanzania border jogs around the mountain just below the 'KENYA' label on the image above.]

The seasonal snowcover situation on Kilimanjaro is discussed below; the extent did not increase during May.

Included in the EO article are some helpful references detailing the human impact of this developing East Africa drought.

Dry-season forecast: above-average ablation

The long rains (Masika) of 2019 are concluding with virtually no snow accumulation on Kilimanjaro glaciers, in stark contrast to last year's long-rain season - demonstrating the extreme interannual variability of precipitation at the summit.

The Sentinel-2 image above from 2 days ago (14 May) reveals a largely snow-free crater. Small areas of last year's snow persist (e.g., east of the Northern Icefield, adjacent to the Furtwängler Glacier). Elsewhere, only a dusting of snow can be seen on Kibo's south side - which not coincidentally spans the elevation range and azimuth of remnant glaciers there! (Very preliminary analysis suggests that the responsible snowfall event was somewhat more extensive, yet we know that at this SSW sector of the mountain, convection enhances snowfall and clouds reduce ablation.)

During the long rains last year - extending from 27 February until this date (16 May) - net accumulation of snow on the Northern Icefield was over one meter (as discussed here). Contrast this with 2019 long rain accumulation, shown in the figure below (blue line); prior to the minor event last week the AWS recorded a net lowering (ablation) of over 30 cm. Additional long rain snowfall may still occur this year, however, the long rains rarely extend into June at the summit.

Absent a major event bringing sufficient snow to reduce solar radiation penetration (e.g., 30-50 cm), the forthcoming extended dry season will probably begin with a snow-free crater. As a result, ablation of both horizontal and vertical glacier surfaces is likely to be dramatic in the months ahead.

(The timelapse image below provides a perspective on summit snowcover since early August of 2018. Within the crater, note the persistence of long-rain accumulation through the dry season, and the ephemeral nature of spatially-extensive-but-thin accumulation during the period February to April 2019.)

South-side glacier changes

The images above depict how Kibo's south-side glaciers have changed in area and thickness over the past 13 years. Thanks to Catrin Stadelmann and her advisor Thomas Mölg for sharing them (Friedrich-Alexander-University (FAU) in Erlangen-Nürnberg, Germany).

Note that both snow and ice are visible in these images, particularly the lower one (Jan. 2019). The largest glacier shown is the Kersten, which Dr. Mölg has published extensively on. Shortly after 2006, a gap began widening between the upper ice and the steeper slope portion of the Kersten. Similarly, a gap also formed between the Kersten and the Decken Glacier to the east (right-hand side of the Kersten). The Decken has gradually narrowed, and very little ice remains today. On the Kersten's left (western) side, remains of the Heim Glacier are visible in 2006; the lower-most extent of this glacier was still present by 2019, surrounded by considerable transient snowcover in the image above.

2018 long rains review

Nature does not follow calendars... but yesterday marks the typical beginning of the northern Tanzania "long rains season". Coincidentally, the long rains last year (2018) began precisely on March 1st (see earlier posts, beginning with this one). Images acquired on the day prior, both last year and this year, are shown above (Sentinel-2 L1C).

Despite partial cloud cover, both images depict limited snowcover other than on glaciers (e.g., north-facing side of the Uhuru Peak summit ridge, the crater's south rim). Most important to this discussion is that the summit crater (approximately circled) is largely free of snow. The 2019 image shows some recent snow on the northern flanks, which was present to a lesser extent on mid-February images (not shown).

Even limited snowcover at the end of February (images above) is in stark contrast to the same time in 2000. Note in our prior post (link) that a snow shovel is visible; don't be fooled by this, for there was neither snow nor firn anywhere on the glacier or within the crater. Indeed, this was an exceptionally dry period which continued through the long rains of 2000 (see figure below; red line); March through May snowfall that year totaled only 26 cm, the least of any long-rain season in our period of record.

As the long rains concluded in mid-May last year, snowcover on the mountain was extensive - as depicted in a Sentinel image from the 29th (below). Indeed, the daily snowfall total at the AWS for the 2018 long rains was double the 19-year average, resulting in more than 1 m of net accumulation. The graph below shows how anomalous this accumulation (thick blue line; 2001-2017 as thin blue lines, 2000 in red).

With even an average short rains last year (typically Nov-Dec), could crater snowcover have persisted until these next, 2019 long rains? Quite possibly! Instead, the 2018 short rains included just 2-3 minor accumulation events, plus early snowfall during our late October fieldwork (link), for a total accumulation of less than 20 cm. By Christmas, crater snowcover was patchy. Then, despite a mid-January event, ablation predominated; by yesterday (see above) the crater was largely snow-free.

In contrast, the Northern Icefield surface at the AWS gained mass over the past 12 months, increasing in height by nearly 50 cm. Higher reflectivity and less re-radiated longwave energy from below (i.e., ice vs. dark volcanic soil) are among the factors.

In summary, the extent of 2018 accumulation and it's persistence demonstrates the sensitive balance of processes governing Kilimanjaro's summit glaciers. If seasonal snowcover does ever persist in the crater through an entire year, retention will be easier the next year and subsequently become even easier. This idea is explored in Kaser et al. (2010), and 2018 observations strengthen the argument!