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February weather on
Kilimanjaro is often characterized by a dry interval, between the Short
Rains of approximately Nov/Dec, and Long Rains within the Mar/Apr/May
time period. As noted previously, the Short Rains brought considerable
rain to the mountain this year, with snow up high, beginning in early
October. That wet period appears to have ended.
The upper image from 2 February shows patchy snowcover on the upper 1000
meters of the mountain's south side, as viewed from above Moshi (Simon Mtuy credit). Distinguishing remnants of the former Southern Icefield
from snowcover is difficult here.
The second image above was acquired today by the ESA Sentinel-2 satellite, revealing continuous snowcover within the summit caldera, and
on the upper slopes. The stable-weather cumulus clouds visible here appear only slightly more
extensive than those on the day before (top image).
Although telemetry of data from the Northern Icefield (NIF) weather
station is not currently available (budget constraints), several recent
reports from climbers confirm what the images depict. On 23 January,
collaborator Sarah Konrad visited the NIF and measured a mean snowdepth
of ~0.60 m around the weather station. Shortly thereafter (28 Jan.),
Simon was above the Western Breach in the Furtwängler Glacier area, reporting "almost one meter of snow."
Images below show Simon's camp at Arrow Glacier on the 27th, looking
south across the Western Breach, and a Furtwängler Glacier
remnant near Crater Camp (Sarah Konrad credit). Finally, a photo of the NIF weather
station from Sarah reveals that the equipment is overdue for a "service
visit". Fortunately, planning is underway to visit the station later this month!
[UPDATE 02/04: Our friend
Timba keeps close tabs on Kilimanjaro weather from Moshi, in the
interest of safety for the many guides and porters working on the
mountain. It was Timba who inspired our analysis of how tropical
cyclones might influence snowfall on the mountain (Collier et al., 2019).
Timba wrote today, emphasizing how wet the region has been in recent
months, especially at the end of September and through most of October
2019. As he points out, this is the time when the Indian Ocean Dipole (IOD) was very strongly positive, a water temperature pattern associated with heavy rain in eastern Africa - and bushfires in Australia (read more here and here).
So, has stable weather really returned to Kilimanjaro? Although the IOD
has returned to a neutral pattern, older friends of Timba's equate the
current rainfall pattern with that of Oct. 1988 to June 1989 - when the
two rainy seasons merged into one long wet season.]
The wet 2019 short rains
continue, according to both satellite imagery and reports from the
Kilimanjaro region. Simon Mtuy wrote today that the mountain has been in
clouds for the past three days, with heavy rain last night.
Above is a glimpse of the mountain two hours ago, from TPC sugar plantations (above Moshi).
Active convection continues over the anomalously-warm, western Indian
Ocean. Tropical Cyclone 06A is forecast to move southwest to Somalia on a
track toward Lake Victoria, with landfall on 6 December bringing heavy
rainfall and high winds; not what eastern Africa needs this year.
In addition to cyclone 06A, another cyclone is forming on the other side of the Equator. Rarely do cyclones form on both sides (circulating in opposite directions). Read more about this situation, and the vigorous convection expected, here. [credit Severe Weather Europe]
The upper photo provides
another perspective on Kilimanjaro snow, complementing those of the
previous post on this blog. It was sent recently by Simon of SENE, taken
from Moshi in the first few days of November. On the satellite image
above from 5 November, snowcover is reduced within the large summit
caldera relative to that of 26 October, yet the snowline on the
southwest flank appears even lower. Today's Sentinel-2 image (10
November, not shown) reveals a fresh dusting over the entire mountain,
with higher amounts just west of Reusch Crater.
Simon wrote of anomalous October rainfall in the area, with a frequency
more like that of the long-rain season. This appears to have also been
the case for a larger region of East Africa, especially Kenya, southern
Somalia and southern Ethiopia - and has led to flooding to the north and
east of Kilimanjaro. The situation is shown clearly on a European
Commission map for 5 November, from the Emergency Response Coordination Centre (ERCC). [Kilimanjaro can be seen, in shaded relief, where the northern border of Tanzania jogs a bit; it is southwest of the flooded area in Kenya (red dots).]
Why has the region been so wet during October? One good possibility is
related to sea surface temperatures in the western Indian Ocean:
anomalously warm water! Warmer than normal SSTs in the west, with cool
SSTs in the east, sets up a positive Indian Ocean Dipole (IOD) event,
associated with increased convection and precipitation over East Africa.
During September the IOD strengthened markedly, becoming one of the
most-positive events in many decades. Further information can be found
here. Once precipitation data from the mountain are available, we will
have a better understanding on how the 2019 IOD event is impacting the
Kilimanjaro region.
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!
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.
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.
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.
