Measured daily precipitation sums over Central Sulawesi for the period 1981-1999

Data compiled within the IMPENSO project. The Impact of ENSO on Sustainable Water Management and the Decision-Making Community at a Rainforest Margin in Indonesia (IMPENSO), http://www.gwdg.de/~impenso, was a German-Indonesian research project (2003-2007) that has studied the impact of ENSO (El Nino-Southern Oscillation) on the water resources and the agricultural production in the PALU RIVER watershed in Central Sulawesi. ENSO is a climate variability that causes serious droughts in Indonesia and other countries of South-East Asia. The last ENSO event occurred in 1997. As in other regions, many farmers in Central Sulawesi suffered from reduced crop yields and lost their livestock. A better prediction of ENSO and the development of coping strategies would help local communities mitigate the impact of ENSO on rural livelihoods and food security. The IMPENSO project deals with the impact of the climate variability ENSO (El Niño Southern Oscillation) on water resource management and the local communities in the Palu River watershed of Central Sulawesi, Indonesia. The project consists of three interrelated sub-projects, which study the local and regional manifestation of ENSO using the Regional Climate Models REMO and GESIMA (Sub-project A), quantify the impact of ENSO on the availability of water for agriculture and other uses, using the distributed hydrological model WaSiM-ETH (Sub-project B), and analyze the socio-economic impact and the policy implications of ENSO on the basis of a production function analysis, a household vulnerability analysis, and a linear programming model (Sub-project C). The models used in the three sub-projects will be integrated to simulate joint scenarios that are defined in collaboration with local stakeholders and are relevant for the design of coping strategies.

Tree ring record from a Redwood

The permanent exhibition of the Staatliches Museum für Naturkunde Stuttgart, Schloss Rosenstein, contains the cross section of a California coast redwood tree (Sequoia sempervirens) from Humboldt County, California, felled in 1966 reveals 1285 annual tree-rings. The measured thicknesses of tree-rings comprise a time series with distinct thickness variations, which are the expression of changing environmental conditions such as precipitation and fog. These factors are controlled by nearby coastal upwelling, which is again influenced by El Nino-Southern Oscillation (ENSO), and which in turn can be influenced by variations of solar radiance. In fact, the tree-ring time series comprises evidence for three orders of solar cycles that may have indirectly controlled tree growth: Hale cycle (21.9 yr), Gleissberg cycle (88.6 yr) and De Vries cycle (209.8 yr). These interpretations should, however, be treated with caution, because it is the only cross section known and the acquirement of reliable data requires cross dating of several sections. (was: The cross section of a California coast redwood tree (Sequoia sempervirens) felled in 1966 reveals 1285 annual tree-rings. The measured thicknesses of tree-rings comprise a time series with distinct thickness variations, which are the expression of changing environmental conditions such as precipitation and fog. These factors are controlled by nearby coastal upwelling, which is again influenced by El Nino-Southern Oscillation (ENSO), and which in turn can be influenced by variations of solar radiance. In fact, the tree-ring time series comprises evidence for three orders of solar cycles that may have indirectly controlled tree growth: Hale cycle (21.9 yr), Gleissberg cycle (88.6 yr) and De Vries cycle (209.8 yr).

Individual foraminifera variability from the western and eastern equatorial Pacific during the Late Holocene and Last Glacial Maximum

El Niño-Southern Oscillation (ENSO) is a major source of global interannual variability, but its response to climate change is uncertain. Paleoclimate records from the Last Glacial Maximum (LGM) provide insight into ENSO behavior when global boundary conditions (ice sheet extent, atmospheric partial pressure of CO2) were different from those today. In this work, we reconstruct LGM temperature variability at equatorial Pacific sites using measurements of individual planktonic foraminifera shells. A deep equatorial thermocline altered the dynamics in the eastern equatorial cold tongue, resulting in reduced ENSO variability during the LGM compared to the Late Holocene. These results suggest that ENSO was not tied directly to the east-west temperature gradient, as previously suggested. Rather, the thermocline of the eastern equatorial Pacific played a decisive role in the ENSO response to LGM climate.

Dahlak coral d18O record (DGII) from the southern Red Sea

Coral palaeoclimatic studies are under way at many sites throughout the wet tropics. However, arid environments have received less attention. Here we report a high-resolution, 63 yr record of coral d18O and d13C extracted from a Porites colony from the Dahlak Archipelago, off the Eritrean coast, in the southern Red Sea. The annual cycles of the coral d18O and d13C are inversely related while their inter-annual variations show a strong positive correlation, with similar inter-decadal trends. Inter-annual variations in coral d18O show a relatively weak correlation with the southern Red Sea SST, but are strongly correlated with the Indian Ocean SST, especially on the decadal time-scale. The range of the inter-annual variations in the coral d18O is high compared to changes in local SST, due to the amplifying effect of simultaneous changes in water isotopic composition. Due to this amplification of the climate signal the coral provides a better indication of regional oceangraphic behaviour than the local SST record. The norrtheast monsoon signal in the coral d18O dominates the mean annual signal and shows the best correlation with the instrumental data sets. It appears that variations in the coral d18O are controlled mainly by variations in the intensity of surface water influx from the Indian Ocean to the Red Sea during the winter northeast monsoon. Of particular significance is that the decadal time-scale variations in the coral skeletal d18O are closely correlated with both the Indian Ocean SST and with variations in the Pacific-based Southern Oscillation index. That is, isotopically light coral skeleton, indicating strong NE monsoon Red Sea inflow, correlates with periods of high Indian Ocean SST and with predominantly negative (El Nino) phases of the Southern Oscillation. The simultaneous nature of inter-decadal changes in Asian monsoon and ENSO behaviour suggest pan-Indo-Pacific tropical climate reorganisation and evolution.

(Table S2) The reconstructed sea surface temperature (SST) over the eastern equatorial Pacific

Abundant hydroclimatic evidence from western Amazonia and the adjacent Andes documents wet conditions during Heinrich Stadial 1 (HS1, 18-15 ka), a cold period in the high latitudes of the North Atlantic. This precipitation anomaly was attributed to a strengthening of the South American summer monsoon due to a change in the Atlantic interhemispheric sea surface temperature (SST) gradient. However, the physical viability of this mechanism has never been rigorously tested. We address this issue by combining a thorough compilation of tropical South American paleorecords and a set of atmosphere model sensitivity experiments. Our results show that the Atlantic SST variations alone, although leading to dry conditions in northern South America and wet conditions in northeastern Brazil, cannot produce increased precipitation over western Amazonia and the adjacent Andes during HS1. Instead, an eastern equatorial Pacific SST increase (i.e., 0.5-1.5 °C), in response to the slowdown of the Atlantic Meridional Overturning Circulation during HS1, is crucial to generate the wet conditions in these regions. The mechanism works via anomalous low sea level pressure over the eastern equatorial Pacific, which promotes a regional easterly low-level wind anomaly and moisture recycling from central Amazonia towards the Andes.