Evapoclimatonomy modelling of four restoration stages following Krakatau’s 1883 destruction

Abstract

Botanists have established that plant recolonization on Krakatau Island (6°S, 106°E) following the August 1883 eruption occurred in four distinct stages: (1) 1883–1886: bare rocks and sterile ash and pumice desert, (2) 1886–1919: grasses and ferns forming savanna, (3) 1919–1933: strand forest and young tree communities and (4) 1933–Present: tropical rainforest. Assuming no changes in macro climate conditions, meso–micro climates for each stage are assessed based on the analysis of soil water balance using climatonomic modelling techniques. Climate records at Jakarta (about 100 km to the east of Krakatau) were used to determine the climatonomic parameters for the rainforest climax; the parameter values for the transient stages were interpolated between values for climax and estimates for the volcanic ash desert. Large immediate runoff and small immediate evaporation are characteristics of the extreme anomaly of pumice and ash desert. The extremely low soil moisture of 21 mm in September (at the end of the dry season) is caused by high immediate runoff due to lack of vegetation cover. The average residence-time during this stage is, however, a little longer than 1 month. The abundant monsoon rains (2 m per year) collected in surface depressions in the lava rocks filled with ashes were most likely to offer relatively favourable conditions for the germination of living propagules, even during the first years after the eruption, due to significant evaporative cooling. In the savanna phase the evapotranspiration minimum was already twice as large in comparison with the desert extreme, and almost back to normal in the young forest phase. Keywords: Krakatau; Evapoclimatonomy; Rainforest climax; Soil moisture; Evapotranspiration