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The Andes Cordillera acts as regional "Water Towers" for several countries and encompasses a wide range of ecosystems and climates. Several hydroclimatic changes have been described for portions of the Andes during recent years, including glacier retreat, negative precipitation trends, an elevation rise in the 0° isotherm, and changes in regional streamflow regimes. The Temperate-Mediterranean transition (TMT) zone of the Andes (35.5°-39.5°S) is particularly at risk to climate change because it is a biodiversity hotspot with heavy human population pressure on water resources. In this paper we utilize a new tree-ring network of Austrocedrus chilensis to reconstruct past variations in regional moisture in the TMT of the Andes by means of the Palmer Drought Severity Index (PDSI). The reconstruction covers the past 657 years and captures interannual to decadal scales of variability in late spring-early summer PDSI. These changes are related to the north-south oscillations in moisture conditions between the Mediterranean and Temperate climates of the Andes as a consequence of the latitudinal position of the storm tracks forced by large-scale circulation modes. Kernel estimation of occurrence rates reveals an unprecedented increment of severe and extreme drought events during the last century in the context of the previous six centuries. Moisture conditions in our study region are linked to tropical and high-latitude ocean-atmospheric forcing, with PDSI positively related to Niño-3.4 SST during spring and strongly negatively correlated with the Antarctic Oscillation (AAO) during summer. Geopotential anomaly maps at 500-hPa show that extreme dry years are tightly associated with negative height anomalies in the Ross-Amundsen Seas, in concordance with the strong negative relationship between PDSI and AAO. The twentieth century increase in extreme drought events in the TMT may not be related to ENSO but to the positive AAO trend during late-spring and summer resulting from a

The Citarum river basin of western Java, Indonesia, which supplies water to 10 million residents in Jakarta, has become increasingly vulnerable to anthropogenic change. Citarum's streamflow record, only similar to 45 years in length (1963-present), is too short for understanding the full range of hydrometeorological variability in this important region. Here we present a tree-ring based reconstruction of September-November Citarum streamflow (AD 1759-2006), one of the first such records available for monsoon Asia. Close coupling is observed between decreased tree growth and low streamflow levels, which in turn are associated with drought caused by ENSO warm events in the tropical Pacific and Indian Ocean positive dipole-type variability. Over the full length of record, reconstructed variance was at its weakest during the interval from similar to 1905-1960, overlapping with a period of unusually-low variability (1920-1960) in the ENSO-Indian Ocean dipole systems. In subsequent decades, increased variance in both the streamflow anomalies and a coral-based SST reconstruction of the Indian Ocean Dipole Mode signal the potential for intensified drought activity and related consequences for water supply and crop productivity in western Java, where much of the country's rice is grown.

For the analysis of trends in weather extremes, we introduce a diagnostic variable, the exceedance product, which combines intensity and frequency of extremes. We separate trends in higher moments from trends in mean or standard deviation and use bootstrap resampling to evaluate statistical significances. Application to daily meteorological records from Potsdam (1893–2005) and Prague (1775–2004) reveals that extremely cold winters occurred only until mid-20th century, whereas warm winters show upward trends. These were significant changes in higher moments of the temperature distribution. In contrast, trends in summer temperature extremes (e.g., 2003 European heatwave), can be explained by linear changes in mean or standard deviation. While precipitation at Potsdam does not exhibit pronounced trends, dew point displays an enigmatic change from maximum extremes during the 1960s to minimum extremes during the 1970s., Zur Untersuchung von Trends vonWetterextremen wird ein neuartiges „Wirkungsmaß” eingeführt, das Produkt der Extremwertübertreffung, welches die beiden Aspekte „Stärke” und „Häufigkeit” miteinander verbindet. Es werden Trends in höheren Momenten von Trends in Mittelwert und Standardabweichung getrennt sowie Bootstrap-Verfahren angewendet, um die statistische Signifikanz auszuwerten. Bei der Verwendung von meteorologischen Daten in täglicher Auflösung von Potsdam (1893–2005) und Prag (1775–2004) zeigt sich, dass extrem kalte Winter nur bis Mitte des 20. Jahrhundert auftraten, wohingegen warme Winter einen Aufwärtstrend aufweisen, welche signifikante Änderungen in höheren Momenten der Temperaturverteilung darstellen. Im Gegensatz dazu kann der Trend von Sommer-Temperaturextremen (z.B. die Hitzewelle im Jahr 2003 in Europa) durch Änderungen in Mittelwert und Standardabweichung erklärt werden. Während der Niederschlag in Potsdam keine ausgeprägte Trends zeigt, weist der Taupunkt einen rätselhaften Übergang von Maximumextremen in den 1960ern zu Minimumextremen in den 1970ern auf.

The interplay of the El Niño Southern Oscillation, Asian monsoon and Indian Ocean Dipole (IOD)1-3 drives climatic extremes in and around the Indian Ocean. Historical4,5 and proxy6-9 records reveal changes in the behaviour of the El Niño Southern Oscilla

Ice core records of methanesulfonic acid (MSA) from three sites around the Weddell Sea are investigated for their potential as sea ice proxies. It is found that the amount of MSA reaching the ice core sites decreases following years of increased winter sea ice in the Weddell Sea; opposite to the expected relationship if MSA is to be used as a sea ice proxy. It is also shown that this negative MSA-sea ice relationship cannot be explained by the influence that the extensive summer ice pack in the Weddell Sea has on MSA production area and transport distance. A historical record of sea ice from the northern Weddell Sea shows that the negative relationship between MSA and winter sea ice exists over interannual (7-year period) and multidecadal (20-year period) timescales. National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data suggest that this negative relationship is most likely due to variations in the strength of cold offshore wind anomalies traveling across the Weddell Sea, which act to synergistically increase sea ice extent (SIE) while decreasing MSA delivery to the ice core sites. Hence our findings show that in some locations atmospheric transport strength, rather than sea ice conditions, is the dominant factor that determines the MSA signal preserved in near-coastal ice cores. A cautious approach is thus required in using ice core MSA for reconstructing past sea ice conditions, including the need for networks of ice core records and multiproxy studies to assess the significance of past MSA changes at different locations around Antarctica.

Soil erosion is a key socio-economic and environmental problem in Kenya, which has been poorly documented due to the lack of long, continuous records. Here we present Ba/Ca records from Porites corals from the Malindi coral reef documenting the flux of suspended sediment from the Sabaki River with a sub-weekly resolution for the last 300 years. While sediment flux from the Sabaki River is almost constant between 1700 and 1900, a continuous rise in sediment flux is observed since 1900, first due to British settlements and afterwards due to steadily increasing demographic pressure on land use. The peak in suspended sediment load and hence soil erosion occurred between 1974 and 1980 when there is a five to tenfold increase relative to natural levels. This is attributed to the combined effects of dramatically increasing population, unregulated land use, deforestation and severe droughts in the early 1970's. We conclude that despite laudable attempts to instigate soil conservation measures, it is unlikely that there will be a sustainable reduction in soil erosion without a significant improvement in socio-economic conditions.

One of our major aims as Earth System scientists is to predict how the Earth will respond to changes and perturbations in the future. The models and concepts that are used to do this are based on physical laws and information obtained from observations of the past. New paleoclimate records are crucial for a test of our current understanding. This process of testing is particularly important for the credibility of the science: by making predictions that can be tested against observation, we make it clear that our science is reaching the "Popperian" threshold [Popper, 1963], requiring that hypotheses be falsifiable. The imminent appearance of an ice core record of atmospheric CO2 covering the last 740,000 years prompted some of us to issue a challenge at the end of last year [Wolff et al., 2004] - for the modelling community to predict, based on current knowledge, what the record will look like. In this article we describe the submissions to the challenge, so that the concepts underlying the predictions can be explained and discussed when the measured data appear later this year.

XTREND consists of the following methodical Parts. Time interval extraction (Part 1) to analyse different parts of a time series; extreme events detection (Part 2) with robust smoothing; magnitude classification (Part 3) by hand; occurrence rate estimation (Part 4) with kernel functions; bootstrap simulations (Part 5) to estimate confidence bands around the occurrence rate. You work interactively with XTREND (parameter adjustment, calculation, graphics) to acquire more intuition for your data. Although, using “normal” data sizes (less than, say, 1000) and modern machines, the computing time seems to be acceptable (less than a few minutes), parameter adjustment should be done carefully to avoid spurious results or, on the other hand, too long computing times. This Report helps you to achieve that. Although it explains the statistical concepts used, this is generally done with less detail, and you should consult the given references (which include some textbooks) for a deeper understanding.