A Markov modulated Poisson process model for rainfall increments

The problems encountered when using traditional rectangular pulse hierarchical point processmodels for fine temporal resolution and the growing number of available tip-time records suggest that rainfall increments from tipping-bucket gauges be modelled directly. Poisson processes are used with an arrival rate modulated by a Markov chain in Continuous time. The paper shows how, by using two or three states for this chain, much of the structure of the rainfall intensity distribution and the wet/dry sequences can be represented for time-scales as small as 5 minutes.

Prehistoric Pinus woodland dynamics in an upland landscape in northern Scotland: the roles of climate change and human impact

Pollen, microscopic charcoal, palaeohydrological and dendrochronological analyses are applied to a radiocarbon and tephrochronologically dated mid Holocene (ca. 8500–3000 cal B.P.) peat sequence with abundant fossil Pinus (pine) wood. The Pinus populations on peat fluctuated considerably over the period in question. Colonisation by Pinus from ca. 7900–7600 cal B.P. appears to have had no specific environmental trigger; it was probably determined by the rate of migration from particular populations. The second phase, at ca. 5000–4400 cal B.P., was facilitated by anthropogenic interference that reduced competition from other trees. The pollen record shows two Pinus declines. The first at ca. 6200–5500 cal B.P. was caused by a series of rapid and frequent climatic shifts. The second, the so-called pine decline, was very gradual (ca. 4200–3300 cal B.P.) at Loch Farlary and may not have been related to climate change as is often supposed. Low intensity but sustained grazing pressures were more important. Throughout the mid Holocene, the frequency and intensity of burning in these open Pinus–Calluna woods were probably highly sensitive to hydrological (climatic) change. Axe marks on several trees are related to the mid to late Bronze Age, i.e., long after the trees had died.

Peat, pine stumps and people: interactions behind climate, vegetation change and human activity in wetland archaeology at Loch Farlary, Northern Scotland

First paragraph: In 1993, a peat-cutter, Bruce Field, working on the blanket peat bank he rented from the Sutherland Estate by Loch Farlary, above Golspie in Sutherland (fig 1), reported to Scottish Natural Heritage and Historic Scotland several pieces of pine wood bearing axe marks. Their depth in the peat suggested the cut marks to be prehistoric. This paper summarizes the work undertaken to understand the age and archaeological significance of this find (see also Tipping et al 2001 in press). The pine trees were initially thought to be part of a population that flourished briefly across northern Scotland in the middle of the Holocene period from c 4800 cal BP (Huntley, Daniell & Allen 1997). The subsequent collapse across northernmost Scotland of this population, the pine decline, at around 4200-4000 cal BP is unexplained: climate change has been widely assumed (Dubois & Ferguson 1985; Bridge, Haggart & Lowe 1990; Gear & Huntley 1991) but anthropogenic activity has not been disproved (Birks 1975; Bennett 1995). It was hypothesized that the Farlary find would allow for the first time the direct link between human woodland clearance and the Early Bronze Age pine decline.