Highest telescope

Reconstruction of seasonal precipitation in Hawai'i using high-resolution carbon isotope measurements across tree rings

Climate change has increased global mean surface temperatures and altered hydrological processes, and projections suggest that these changes will accelerate. As seasonal precipitation patterns change, so will the soil resources available for plants. In the midwestern United States, winter temperatures and precipitation are expected to increase, while snowfall is expected to be reduced. Reduced snowpack could lead to greater frost damage and alter the timing and amount of plant available resources at the start of the growing season. In the summer, precipitation is expected to decrease, and variability is expected to increase, creating longer and more frequent dry periods. In temperate forests, herbaceous understory plants and woody plants in early developmental stages are expected to be highly sensitive to changes in abiotic conditions. Here, we study how seasonal changes in precipitation affect the timing and availability of resources in a temperate deciduous forest. Further, we examine how changes in abiotic conditions influence understory composition and woody plant recruitment. We established a fully factorial experiment that manipulated winter snowfall and summer precipitation to create wet, dry, and control (ambient) conditions in a temperate deciduous forest near West Lafayette, Indiana, USA. We found that large changes in winter and summer precipitation appeared to affect forest processes independently of one another, and changes in seasonal precipitation altered understory composition minimally and had little to no effect on mineralization rates. The recruitment of woody plant species may be more sensitive to altered precipitation, as snow removal lowered germination rates and wet summer conditions lowered relative growth of a woody plant species, Lindera benzoin. In general, though, ecological processes in this forest understory were relatively resistant to change, at least in the short timeframe of this experiment.

ABSTRACTWe investigated short‐ and long‐term changes in total and extreme summer precipitation and the characteristic patterns of atmospheric circulation and sea surface temperature (SST) anomalies related to wet summers over South Korea. Over the last century (1913–2012), the total and extreme summer precipitation showed a significant increase of 2.62 and 4.45% decade−1, respectively. Because extreme summer precipitation increased more rapidly than total summer precipitation, the contribution of extreme precipitation to total precipitation increased significantly by 2.48% decade−1. A two‐peak rainy season was substantially intensified, with a slight shift and a large increase of precipitation during the monsoon break period, indicating a shortening of the monsoon break period. The 20‐year return values of daily maximum precipitation increased at all stations except Mokpo, showing changes in the frequency of extreme events. During the last 40 years (1973–2012), the pattern of change in the precipitation indices was spatially heterogeneous, with a particularly significant increasing trend in extreme summer precipitation over the North‐central portion of western South Korea. When compared with long‐term trends over 1912–2012, recent short‐term trends showed more rapid increases in all precipitation indices, with the exception of the number of consecutive dry days. In addition, the number of consecutive wet days (CWD) increased significantly during the last 40 years, whereas the long‐term trend over the last century for CWD was not significant. These regional trends were confirmed by field significance at the 90% confidence level. From the composite analysis results, the positive anomalous North Pacific subtropical high, intensification of the upper‐level westerly Jet over Korea and its vertical coupling with the anomalous strong low‐level westerlies, and anomalous warm SST values in the western North Pacific region were linked to recent increases in extreme summer precipitation.

Precipitation during winter months of December, January, and February over northwest India is important for the production of winter crops as well as for glacial accumulation which goes on to feed major rivers in India with fresh water supply. Winter precipitation over this region is due to the movement of synoptic systems approaching from the Mediterranean known as Western Disturbances (WDs). So far, spatial pattern of winter precipitation over this region has not been studied using different RCMs. The present study evaluates the regional climate model employed in Coordinated Regional Climate Downscaling Experiment in South Asia (CORDEX-South Asia) framework to characterize winter precipitation over northwest India and Karakoram region. There are 16 CORDEX-South Asia experiments with 3 regional climate models (RCM) driven with 16 global climate models (GCM). Precipitation climatology is calculated for different RCM along with their ensemble. All the experiments show a wet bias over the region. The selection of best performing RCM is identified using various statistical analyses. The CORDEX experiment run by EC_EARTH RCM with RCA4 GCM developed by Swedish Meteorological and Hydrological Institute (SMHI) is identified as the best performing model when compared with observation. The change in future seasonal mean precipitation is assessed over northwest India and Karakoram region under two representation concentration pathways (RCP4.5 and RCP8.5) scenarios. A positive change in precipitation is observed over Karakoram region under the two RCP scenarios for near future and far future periods. The magnitude of precipitation change is found to be less over the study area under RCP 8.5 scenario for near future period compared to other scenario and time period.

Geographical assessments on the relationship between climate variability and crop production are important for planning adaptation programs to climate change impacts on Asian rice production. This paper analyses the seasonal precipitation consequences to irrigated crop yields, in opposition to the idea that irrigated crop yields are not affected by precipitation changes. Geostatistical methods are applied to assess changes in the patterns of seasonal precipitation and corresponding changes in the Boro crop production in Bangladesh. Surfaces depicting changes in the monsoon, non-monsoon and total precipitation from 2006 to 2007, and changes in three varieties of Boro crop yield and Total Boro yield from 2006-2007 to 2007-2008 crop year are generated through Splines, Inverse Distance Weighting and Ordinary Kriging methods. Performance evaluation of these models is also performed. The relationships between the surfaces of different precipitation seasons and the surfaces of different Boro yield seasons are then assessed. The results show that there is a significant correlation between seasonal precipitation changes and Boro yield changes with notable correlation coefficients and similarity in the patterns. A significant conformity of the high precipitation zones to the high Boro yielding zones is also depicted.

Speleothem δ13C in monsoonal China differs from speleothem δ18O, which is widely used as a climatic proxy for several complex control reasons. Nevertheless, δ13C records have the potential to reveal the implications of hydroclimatic changes. This study reports a speleothem δ13C record from Didonghe (DDH) Cave in central China spanning 34 to 13 kyr BP. After we investigated the factors that influence speleothem δ13C, we found that the δ13C record showed that DDH Cave can prompt directional shifts via local hydroclimatic changes, such as in vegetation types, biomass, and rock–water interaction processes, suggesting that δ13C is mainly controlled by the local hydroclimate. Ensemble empirical mode decomposition (EEMD) results revealed a coupling relationship between δ18O and δ13C on multiple timescales, which suggested that changes in precipitation caused by large-scale monsoonal circulation are controlled by regional hydrological conditions to a great extent. However, the hydrological conditions of the cave were relatively mild and humid during the last glacial maximum (LGM), which revealed the impact of evaporation on changes in the region’s hydrological conditions. We also found that the δ18O and δ13C profiles decoupled when δ13C changed with a shift in the location of the westerly during HS1. The δ13C record correlates well with other paleoclimate records, suggesting that regional hydrological conditions are also modulated by the Earth’s internal and external driving factors.

Tropical montane cloud forests are ecosystems intrinsically linked to a narrow range of geographic and meteorological conditions, making them potentially sensitive to small changes in precipitation or temperature. We investigate the potential application of stable isotope analysis to cloud forest dendroclimatology at Monteverde in Costa Rica in order to be able to extract both chronological and paleoclimate information from trees without annual growth rings. High‐resolution δ18O measurements are used to identify regular cycles in wood of up to 9‰, which are associated with seasonal changes in precipitation and moisture sources. The calculated annual growth rates derived from the isotope time series match those observed from long‐term basal growth measurements. Interannual variability in the oxygen isotope ratio of lower forest trees is primarily related to interannual changes in wet season precipitation. Forward modeling independently supports our detection of both annual chronology and a climate signal. The confirmation of annual chronology and sensitivity to interannual climate anomalies suggests that tropical cloud forest dendroclimatology can be used to investigate local and regional hydroclimatic variability and change.

Interannual variation of seasonal changes of precipitation and moisture transport in the western North Pacific from June to August is studied using global monthly precipitation data, and NCEP-NCAR (National Center for Environmental Prediction-National Center for Atmospheric Research) reanalysis for 20 years from 1979 to 1998. According to the meridional shift of the intense precipitation area and precipitation amounts in June and August to the east of the Philippines, the seasonal changes of precipitation are categorized into Types A and B. Type A is characterized by the northward shift of intense precipitation area and the increase of precipitation from June to August. Type A is further classified into two: Sub-Types A1 and A2. The former is characterized by the gradual increase of precipitation and the northward shift of the intense precipitation area from 6 � Nt o 16 � N. The latter is characterized by a relatively intense precipitation in June, decrease of precipitation in July, significant increase of precipitation with a maximum in August, and the northward shift from 13 � Nt o 22 � N. Type B is characterized by a seasonal change, with almost no precipitation increase nor northward shift from June to August. Difference in the precipitation amount between Types A and B corresponds to the westerly moisture flux originating from the Indian Ocean, and the southerly moisture flux which comes across the equator at the lower level. It is found that the westerly and southerly moisture flux in Type B are much smaller than those in Type A, especially in August. The westerly moisture flux in Sub-Type A2 is larger than that in Sub-Type A1. The seasonal changes of westerly moisture flux show gradual increase in Sub-Type A1, and significant increase in June and August and decrease in July in Sub-Type A2. They are corresponding to those of the precipitation amount, respectively. The large westerly moisture flux and the strong moisture convergence to the east of the Philippines in August in Type A, are associated with the eastward extension of the trough from the Eurasian continent. The northward shift of the intense precipitation area corresponds to the intensification of the eastward extended trough.

Seasonal precipitation changes over the globe during the 20th century simulated by two versions of the Flexible Global Ocean-Atmosphere-Land System (FGOALS) model are assessed. The two model versions differ in terms of their AGCM component, but the remaining parts of the system are almost identical. Both models reasonably reproduce the mean-state features of the timings of the wet and dry seasons and related precipitation amounts, with pattern correlation coefficients of 0.65–0.84 with observations. Globally averaged seasonal precipitation changes are analyzed. The results show that wet seasons get wetter and the annual range (precipitation difference between wet and dry seasons) increases during the 20th century in the two models, with positive trends covering most parts of the globe, which is consistent with observations. However, both models show a moistening dry season, which is opposite to observations. Analysis of the globally averaged moisture budget in the historical climate simulations of the two models shows little change in the horizontal moisture advection in both the wet and dry seasons. The globally averaged seasonal precipitation changes are mainly dominated by the changes in evaporation and vertical moisture advection. Evaporation and vertical moisture advection combine to make wet seasons wetter and enhance the annual range. In the dry season, the opposite change of evaporation and vertical moisture advection leads to an insignificant change in precipitation. Vertical moisture advection is the most important term that determines the changes in precipitation, wherein the thermodynamic component is dominant and the dynamic component tends to offset the effect of the thermodynamic component.

Seasonality of precipitation in the southwestern United States during the late Pleistocene inferred from stable isotopes in herbivore tooth enamel

Influence of seasonal hydrological regimes on benthic macroinvertebrates in two the Brazilian biodiversity hotspots

Teleconnections between El Niño/Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Indian Ocean Dipole (IOD) and Pacific Decadal Oscillation (PDO) and seasonal precipitation regimes over the Yangtze River basin have been analysed based on the rotated empirical orthogonal functions. Results show that ENSO is the leading driver of seasonal precipitation variability over the Yangtze River basin, and the spring precipitation has been influenced by the PDO and ENSO, the summer and autumn precipitation has been influenced by the ENSO and IOD, the winter precipitation has been influenced by the ENSO, IOD and NAO. Furthermore, changes for the seasonal occurrence and intensity of wet days linked to the ENSO, NAO, IOD and PDO indices have also been investigated to discover which is the dominant mechanism driving seasonal precipitation changes. And results indicated that the influences of ENSO, NAO, IOD and PDO on the seasonal occurrence and intensity of precipitation events are complex, such as that the negative PDO event at the same year tends to increase the spring occurrence of precipitation events in the southwestern part of the Yangtze River basin while the positive ENSO event a year earlier tends to increase the spring intensity of precipitation events in the east part of the Yangtze River basin.

Evaluation of different bias-corrected EURO-CORDEX databases and the expected future changes in precipitation over Hungary.

Carbon, nitrogen, and oxygen isotopes of ostrich eggshells provide site-scale Pleistocene-Holocene paleoenvironmental records for eastern African archaeological sites

Abstract. The terrestrial water cycle partitions precipitation between its two ultimate fates: “green water” that is evaporated or transpired back to the atmosphere, and “blue water” that is discharged to stream channels. Measuring this partitioning is difficult, particularly on seasonal timescales. End-member mixing analysis has been widely used to quantify streamflow as a mixture of isotopically distinct sources, but knowing where streamwater comes from is not the same as knowing where precipitation goes, and this latter question is the one we seek to answer. Here we introduce “end-member splitting analysis”, which uses isotopic tracers and water flux measurements to quantify how isotopically distinct inputs (such as summer vs. winter precipitation) are partitioned into different ultimate outputs (such as evapotranspiration and summer vs. winter streamflow). End-member splitting analysis has modest data requirements and can potentially be applied in many different catchment settings. We illustrate this data-driven, model-independent approach with publicly available biweekly isotope time series from Hubbard Brook Watershed 3. A marked seasonal shift in isotopic composition allows us to distinguish rainy-season (April–November) and snowy-season (December–March) precipitation and to trace their respective fates. End-member splitting shows that about one-sixth (18±2 %) of rainy-season precipitation is discharged during the snowy season, but this accounts for over half (60±9 %) of snowy-season streamflow. By contrast, most (55± 13 %) snowy-season precipitation becomes streamflow during the rainy season, where it accounts for 38±9 % of rainy-season streamflow. Our analysis thus shows that significant fractions of each season's streamflow originated as the other season's precipitation, implying significant inter-seasonal water storage within the catchment as both groundwater and snowpack. End-member splitting can also quantify how much of each season's precipitation is eventually evapotranspired. At Watershed 3, we find that only about half (44±8 %) of rainy-season precipitation evapotranspires, but almost all (85±15 %) evapotranspiration originates as rainy-season precipitation, implying that there is relatively little inter-seasonal water storage supplying evapotranspiration. We show how results from this new technique can be combined with young water fractions (calculated from seasonal isotope cycles in precipitation and streamflow) and new water fractions (calculated from correlations between precipitation and streamflow isotope fluctuations) to infer how precipitation is partitioned on multiple timescales. This proof-of-concept study demonstrates that end-member mixing and splitting yield different, but complementary, insights into catchment-scale partitioning of precipitation into blue water and green water. It could thus help in gauging the vulnerability of both water resources and terrestrial ecosystems to changes in seasonal precipitation.