ATE Amboseli Rainfall Data

Sat, 2010-11-20 08:21 by hcroze · Forum/category:

The Amboseli Elephant Research Project has a virtually unbroken series of daily rainfall data since the project began in 1972. Additional monthly summaries from other sources takes the series back to 1967.
Back in June 2008, we reported here on the impending drought based on rainfall deviation from the long-term average.
In this ATE Archive Forum, we intend to open our data archives and present a number of data summaries. We are exploring the best way to make available the underlying data tables for interested researchers. Comments and suggestions on form and content would be most welcome.

The long-term rainfall data series is a composite of measurements at three different meteorological measuring points within 5 km of each other. For the period of 1972-1982 data were taken from Amboseli Park’s Ol Tukai meteorological station, after which the Amboseli Elephant Research Project (AERP) camp rain gauge was then the main data source. Records from the Amboseli Baboon Research Project camp rain gauge were used to fill a small number (n=6) of daily measurement gaps between 1983 and 2002 when the AERP rain gauge was temporarily out of repair. Years 1970-71 and 1972-73 had data completely missing in seven and three months, respectively.

Annual rainfall
Amboseli Rainfall and Dry Season Intensity 1968-2009

In order to get a clear picture of ecosystem stress on the elephants we use Dry Season Intensity (DSI) shown as a line in the graph above. The index, proposed by Keith Lindsay (1994. Feeding ecology and population demography of African elephants in Amboseli Kenya. PhD thesis, University of Cambridge.), estimates the severity of the long dry season in a given year. Calculated as the number of Dry Months (defined as having <20 mm of rain) divided by Annual Rainfall, it is a proxy measure of the extent of plant biomass decline through consumption by herbivores (length of the dry season) relative to plant biomass growth/production (rainfall).

Over two discernible seasons – the ‘short rains’ in November and December (sometimes starting in late October) and the ‘long rains’ from March to the end of May – only some 340 mm falls on average annually in the Amboseli basin. The short dry season between January and February is relatively hot (up to 35º C in February); the longer dry season between June and October can be cold (down to 5ºC in July and August). For purposes of analysis, we have defined an ‘Amboseli Year’ as beginning in November and ending the following October. The Amboseli Year captures more accurately than the calendar year the annual cycle of growth and maturation of vegetation. Since it may take a month for plant growth to respond to rainfall, and since rain may begin to fall some years in October, we have summed monthly rainfall from October through September as the total precipitation for one Amboseli Year.

Monthly rainfall
Monthly Rainfall, 41-year Average