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Showing papers on "Precipitation published in 2001"


Journal ArticleDOI
07 Dec 2001-Science
TL;DR: Human activities are releasing tiny particles (aerosols) into the atmosphere that enhance scattering and absorption of solar radiation, which can lead to a weaker hydrological cycle, which connects directly to availability and quality of fresh water, a major environmental issue of the 21st century.
Abstract: Human activities are releasing tiny particles (aerosols) into the atmosphere. These human-made aerosols enhance scattering and absorption of solar radiation. They also produce brighter clouds that are less efficient at releasing precipitation. These in turn lead to large reductions in the amount of solar irradiance reaching Earth's surface, a corresponding increase in solar heating of the atmosphere, changes in the atmospheric temperature structure, suppression of rainfall, and less efficient removal of pollutants. These aerosol effects can lead to a weaker hydrological cycle, which connects directly to availability and quality of fresh water, a major environmental issue of the 21st century.

3,469 citations


Journal ArticleDOI
17 Aug 2001-Science
TL;DR: The Cariaco Basin record exhibits strong correlations with climate records from distant regions, including the high-latitude Northern Hemisphere, providing evidence for global teleconnections among regional climates.
Abstract: Titanium and iron concentration data from the anoxic Cariaco Basin, off the Venezuelan coast, can be used to infer variations in the hydrological cycle over northern South America during the past 14,000 years with subdecadal resolution. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the Holocene “thermal maximum.” Since ∼5400 years ago, a trend toward drier conditions is evident from the data, with high-amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the “Little Ice Age.” These regional changes in precipitation are best explained by shifts in the mean latitude of the Atlantic Intertropical Convergence Zone (ITCZ), potentially driven by Pacific-based climate variability. The Cariaco Basin record exhibits strong correlations with climate records from distant regions, including the high-latitude Northern Hemisphere, providing evidence for global teleconnections among regional climates.

2,032 citations


Journal ArticleDOI
TL;DR: One-degree daily (1DD) technique is described for producing globally complete daily estimates of precipitation on a 1 deg x 1 deg lat/long grid from currently available observational data as mentioned in this paper.
Abstract: The One-Degree Daily (1DD) technique is described for producing globally complete daily estimates of precipitation on a 1 deg x 1 deg lat/long grid from currently available observational data. Where possible (40 deg N-40 deg S), the Threshold-Matched Precipitation Index (TMPI) provides precipitation estimates in which the 3-hourly infrared brightness temperatures (IR T(sub b)) are thresholded and all "cold" pixels are given a single precipitation rate. This approach is an adaptation of the Geostationary Operational Environmental Satellite (GOES) Precipitation Index (GPI), but for the TMPI the IR Tb threshold and conditional rain rate are set locally by month from Special Sensor Microwave/Imager (SSM/I)-based precipitation frequency and the Global Precipitation Climatology Project (GPCP) satellite-gauge (SG) combined monthly precipitation estimate, respectively. At higher latitudes the 1DD features a rescaled daily Television Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS) precipitation. The frequency of rain days in the TOVS is scaled down to match that in the TMPI at the data boundaries, and the resulting non-zero TOVS values are scaled locally to sum to the SG (which is a globally complete monthly product). The time series of the daily 1DD global images shows good continuity in time and across the data boundaries. Various examples are shown to illustrate uses. Validation for individual grid -box values shows a very high root-mean-square error but, it improves quickly when users perform time/space averaging according to their own requirements.

1,752 citations


Journal ArticleDOI
TL;DR: Using satellite and aircraft observations, it is shown that clouds forming within desert dust contain small droplets and produce little precipitation by drop coalescence, suggesting a possible mechanism for the diminished rainfall.
Abstract: The effect of desert dust on cloud properties and precipitation has so far been studied solely by using theoretical models, which predict that rainfall would be enhanced. Here we present observations showing the contrary; the effect of dust on cloud properties is to inhibit precipitation. Using satellite and aircraft observations we show that clouds forming within desert dust contain small droplets and produce little precipitation by drop coalescence. Measurement of the size distribution and the chemical analysis of individual Saharan dust particles collected in such a dust storm suggest a possible mechanism for the diminished rainfall. The detrimental impact of dust on rainfall is smaller than that caused by smoke from biomass burning or anthropogenic air pollution, but the large abundance of desert dust in the atmosphere renders it important. The reduction of precipitation from clouds affected by desert dust can cause drier soil, which in turn raises more dust, thus providing a possible feedback loop to further decrease precipitation. Furthermore, anthropogenic changes of land use exposing the topsoil can initiate such a desertification feedback process.

706 citations


Journal ArticleDOI
TL;DR: The UVic Earth System Climate Model as discussed by the authors consists of a three-dimensional ocean general circulation model coupled to a thermodynamic/dynamic sea ice model, an energy-moisture balance atmospheric model with dynamical feedbacks, and a thermomechanical land-ice model.
Abstract: A new earth system climate model of intermediate complexity has been developed and its climatology compared to observations. The UVic Earth System Climate Model consists of a three‐dimensional ocean general circulation model coupled to a thermodynamic/dynamic sea‐ice model, an energy‐moisture balance atmospheric model with dynamical feedbacks, and a thermomechanical land‐ice model. In order to keep the model computationally efficient a reduced complexity atmosphere model is used. Atmospheric heat and freshwater transports are parametrized through Fickian diffusion, and precipitation is assumed to occur when the relative humidity is greater than 85%. Moisture transport can also be accomplished through advection if desired. Precipitation over land is assumed to return instantaneously to the ocean via one of 33 observed river drainage basins. Ice and snow albedo feedbacks are included in the coupled model by locally increasing the prescribed latitudinal profile of the planetary albedo. The atmospher...

653 citations


Journal ArticleDOI
TL;DR: In this paper, four state-of-the-art general circulation models (GCMs) were used to assess the hydrologic sensitivity to climate change of nine large, continental river basins (Amazon, Amur, Mackenzie, Mekong, Mississippi, Severnaya Dvina, Xi, Yellow, Yenisei).
Abstract: Climate predictions from four state-of-the-art general circulation models (GCMs) were used to assess the hydrologic sensitivity to climate change of nine large, continental river basins (Amazon, Amur, Mackenzie, Mekong, Mississippi, Severnaya Dvina, Xi, Yellow, Yenisei). The four climate models (HCCPR-CM2, HCCPR-CM3, MPI-ECHAM4, and DOE-PCM3) all predicted transient climate response to changing greenhouse gas concentrations, and incorporated modern land surface parameterizations. Model-predicted monthly average precipitation and temperature changes were downscaled to the river basin level using model increments (transient minus control) to adjust for GCM bias. The variable infiltration capacity (VIC) macroscale hydrological model (MHM) was used to calculate the corresponding changes in hydrologic fluxes (especially streamflow and evapotranspiration) and moisture storages. Hydrologic model simulations were performed for decades centered on 2025 and 2045. In addition, a sensitivity study was performed in which temperature and precipitation were increased independently by 2 °C and 10%, respectively, during each of four seasons. All GCMs predict a warming for all nine basins, with the greatest warming predicted to occur during the winter months in the highest latitudes. Precipitation generally increases, but the monthly precipitation signal varies more between the models than does temperature. The largest changes in the hydrological cycle are predicted for the snow-dominated basins of mid to higher latitudes. This results in part from the greater amount of warming predicted for these regions, but more importantly, because of the important role of snow in the water balance. Because the snow pack integrates the effects of climate change over a period of months, the largest changes occur in early to mid spring when snow melt occurs. The climate change responses are somewhat different for the coldest snow dominated basins than for those with more transitional snow regimes. In the coldest basins, the response to warming is an increase of the spring streamflow peak, whereas for the transitional basins spring runoff decreases. Instead, the transitional basins have large increases in winter streamflows. The hydrological response of most tropical and mid-latitude basins to the warmer and somewhat wetter conditions predicted by the GCMs is a reduction in annual streamflow, although again, considerable disagreement exists among the different GCMs. In contrast, for the high-latitude basins increases in annual flow volume are predicted in most cases.

621 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that global land precipitation has increased by about 9 mm over the twentieth century (a trend of 0.89 mm/decade), which is relatively small compared with interannual and multi-decadal variability.
Abstract: Concern about anthropogenic climate change has heightened the need for accurate information about spatial and temporal variations in precipitation at the Earth’s surface. Large-scale precipitation estimates can be derived from either surface gauge measurements or by satellite remote sensing, both of which have shortcomings. Gauge measurements provide information about trends and variability of monthly precipitation throughout the entire twentieth century, but because of the lack of data from most ocean regions, this information is representative of only about 25–30% of the Earth’s surface. In contrast, satellite (especially multi-platform) measurements provide spatially complete coverage at monthly to subdaily resolution, but do not extend back beyond 1974. Merged gauge–satellite datasets maximize (and minimize) the relative benefits (and shortcomings) of each source type. While these merged products only extend back to 1979, their importance will grow as we move into the new century. Precipitation gauge data indicate that global land precipitation (excluding Antarctica) has increased by about 9 mm over the twentieth century (a trend of 0.89 mm/decade), which is relatively small compared with interannual and multi-decadal variability. Within this century-long trend, global precipitation exhibits considerable variability on decadal time-scales, with departures of up to 40 mm from the century mean of about 950 mm. Regionally, precipitation has increased over most land areas, with the exception of tropical North Africa, and parts of southern Africa, Amazonia and western South America. The dominant mode of interannual variability in global and

550 citations


Journal ArticleDOI
TL;DR: In this article, the authors reviewed previous cloud forest species redistributions in the paleo-record in light of the coming climate changes and concluded that climate change is very likely to upset the current dynamic equilibrium of the cloud forest, which will include biodiversity loss, altitude shifts in species' ranges and subsequent community reshuffling.

511 citations


Journal ArticleDOI
TL;DR: In this paper, an equation that relates the autocorrelation of soil moisture in climate models to seasonality in the statistics of the atmospheric forcing, the variation of evaporation with soil moisture, and persistence in atmospheric forcing as perhaps induced by land atmosphere feedback is proposed.
Abstract: Water balance considerations at the soil surface lead to an equation that relates the autocorrelation of soil moisture in climate models to (1) seasonality in the statistics of the atmospheric forcing, (2) the variation of evaporation with soil moisture, (3) the variation of runoff with soil moisture, and (4) persistence in the atmospheric forcing, as perhaps induced by land atmosphere feedback. Geographical variations in the relative strengths of these factors, which can be established through analysis of model diagnostics and which can be validated to a certain extent against observations, lead to geographical variations in simulated soil moisture memory and thus, in effect, to geographical variations in seasonal precipitation predictability associated with soil moisture. The use of the equation to characterize controls on soil moisture memory is demonstrated with data from the modeling system of the NASA Seasonal-to-Interannual Prediction Project.

449 citations


Journal ArticleDOI
TL;DR: In this paper, three-hourly present weather reports from ∼15,000 stations around the globe and from the Comprehensive Ocean-Atmosphere Data Set from 1975 to 1997 were analyzed for diurnal variations in the frequency of occurrence for various types of precipitation (drizzle, nondrizzle, showery, nonshowery, and snow) and thunderstorms.
Abstract: Three-hourly present weather reports from ∼15 000 stations around the globe and from the Comprehensive Ocean–Atmosphere Data Set from 1975 to 1997 were analyzed for diurnal variations in the frequency of occurrence for various types of precipitation (drizzle, nondrizzle, showery, nonshowery, and snow) and thunderstorms. Significant diurnal variations with amplitudes exceeding 20% of the daily mean are found over much of the globe, especially over land areas and during summer. Drizzle and nonshowery precipitation occur most frequently in the morning around 0600 local solar time (LST) over most land areas and from midnight to 0400 LST over many oceanic areas. Showery precipitation and thunderstorms occur much more frequently in the late afternoon than other times over most land areas in all seasons, with a diurnal amplitude exceeding 50% of the daily mean frequencies. Over the North Pacific, the North Atlantic, and many other oceanic areas adjacent to continents, showery precipitation is most frequ...

425 citations


Journal ArticleDOI
TL;DR: In this paper, the isotopic data are fitted by using a numerical model based on Rayleigh adiabatic condensation process, which shows that the δ-gradient vs. altitude relationship slightly deviates from linearity, due to the lowering of temperature and the consequent increase of the condensation rate of atmospheric vapour.


Journal ArticleDOI
TL;DR: In this paper, the authors reproduce the first-order spatial and temporal patterns in atmospheric dust loading under modern conditions, and show that positive feedbacks initiated by a reduction of dust emissions from natural source areas on both radiative forcing and atmospheric CO2 could substantially mitigate the impacts of land-use changes, and need to be considered in climate change assessments.

Journal ArticleDOI
TL;DR: In this article, a program of individual precipitation events and river water sampling and of water isotopic measurements (δD, δ18O) was carried out during summer 1996 along a northeast/southwest transect of the Tibetan Plateau.
Abstract: A program of individual precipitation events and river water sampling and of water isotopic measurements (δD, δ18O) was carried out during summer 1996 along a northeast/southwest transect of the Tibetan Plateau. The spatial distribution of both δ18O and deuterium excess (d = δD-8*δ18O) of the precipitation reveals three distinct regions. Simulations with a simple isotopic model and seasonal isotopic variations measured at two extreme south and north locations support our interpretation in terms of different summer moisture origins: (1) South of the Himalayan mountains, the moisture provided by the Indian monsoon has been recycled over the Indian peninsula. (2) Between the Himalayas and the Tanggula mountains the oceanic moisture is directly transported from the Bay of Bengal along the Brahmaptra River valley. (3) North of the Tanggula mountains, the moisture is not provided by the monsoon anymore but by continental water recycling.

Journal ArticleDOI
TL;DR: In this article, the change in oxygen isotopic composition of precipitation is modeled using equilibrium fractionation during Rayleigh distillation linked to the thermodynamics of atmospheric ascent and water vapor condensation.

Journal ArticleDOI
TL;DR: In this article, a daily set of surface meteorological forcings, model-derived surface moisture fluxes, and state variables for global land areas for the period of 1979-93 is described.
Abstract: A daily set of surface meteorological forcings, model-derived surface moisture fluxes, and state variables for global land areas for the period of 1979–93 is described. The forcing dataset facilitates global simulations and evaluation of land surface parameterizations without relying heavily on GCM output. Daily precipitation and temperature are based on station observations, daily wind speeds are based on National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis data, and the remaining meteorological forcing variables (shortwave radiation, longwave radiation, and vapor pressure) are derived from the precipitation and temperature series. The Variable Infiltration Capacity (VIC) land surface model is used to produce a set of derived fluxes and state variables, including snow water equivalent, evapotranspiration, runoff, and soil moisture storage. The main differences between the new dataset and other, similar datasets are the daily time step, the use of a sp...

Journal ArticleDOI
TL;DR: In this paper, the percentage of times that seasonal precipitation over land areas was above, near, and below normal during the eight strongest El Nino and La Nina episodes are tabulated, and the significance levels of the posterior probabilities are calculated using the hypergeometric distribution.
Abstract: Extreme phases of the El Nino–Southern Oscillation (ENSO) phenomenon have been blamed for precipitation anomalies in many areas of the world. In some areas the probability of above–normal precipitation may be increased during warm or cold events, while in others below–normal precipitation may be more likely. The percentages of times that seasonal precipitation over land areas was above, near, and below normal during the eight strongest El Nino and La Nina episodes are tabulated, and the significance levels of the posterior probabilities are calculated using the hypergeometric distribution. These frequencies may provide a useful starting point for probabilistic climate forecasts during strong ENSO events. Areas with significantly high or low frequencies or above– or below–normal precipitation are highlighted, and attempts are made to estimate the proportion of land areas with significant ENSO–related precipitation signals. There is a danger of overstating the global impact of ENSO events because o...

Journal ArticleDOI
TL;DR: In this article, a comparison of 8 regional atmospheric model systems was carried out for a three-month late summer/early autumn period in 1995 over the Baltic Sea and its catchment area.
Abstract: A comparison of 8 regional atmospheric model systems was carried out for a three-month late summer/early autumn period in 1995 over the Baltic Sea and its catchment area. All models were configured on a common grid using similar surface and lateral boundary conditions, and ran in either data assimilation mode (short term forecasts plus data assimilation), forecast mode (short term forecasts initialised daily with analyses) or climate mode (no re-initialisation of model interior during entire simulation period). Model results presented in this paper were generally post processed as daily averaged quantities, separate for land and sea areas when relevant. Post processed output was compared against available analyses or observations of cloud cover, precipitation, vertically integrated atmospheric specific humidity, runoff, surface radiation and near surface synoptic observations. The definition of a common grid and lateral forcing resulted in a high degree of agreement among the participating model results for most cases. Models operated in climate mode generally displayed slightly larger deviations from the observations than the data assimilation or forecast mode integration, but in all cases synoptic events were well captured. Correspondence to near surface synoptic quantities was good. Significant disagreement between model results was shown in particular for cloud cover and the radiative properties, average precipitation and runoff. Problems with choosing appropriate initial soil moisture conditions from a common initial soil moisture field resulted in a wide range of evaporation and sensible heat flux values during the first few weeks of the simulations, but better agreement was shown at later times.

Journal ArticleDOI
TL;DR: In this paper, the authors combined both TRMM precipitation radar (PR) and Lightning Imaging Sensor (LIS) data to examine "wet-season" vertical structures of tropical precipitation across a broad spectrum of locations in the global Tropics.
Abstract: Observation of the vertical profile of precipitation over the global Tropics is a key objective of the Tropical Rainfall Measuring Mission (TRMM) because this information is central to obtaining vertical profiles of latent heating. This study combines both TRMM precipitation radar (PR) and Lightning Imaging Sensor (LIS) data to examine “wet-season” vertical structures of tropical precipitation across a broad spectrum of locations in the global Tropics. TRMM-PR reflectivity data (2A25 algorithm) were utilized to produce seasonal mean three-dimensional relative frequency histograms and precipitation ice water contents over grid boxes of approximately 5°–10° in latitude and longitude. The reflectivity histograms and ice water contents were then combined with LIS lightning flash densities and 2A25 mean rainfall rates to examine regional relationships between precipitation vertical structure, precipitation processes, and lightning production. Analysis of the reflectivity vertical structure histograms ...

Journal ArticleDOI
07 Sep 2001-Science
TL;DR: A longterm normalized difference vegetation index (NDVI) data set derived from the Advanced Very High Resolution Radiometer of the National Oceanic and Atmospheric Administration (NOAA), coupled with a historical climate data set, should constitute a useful and powerful data source, because NDVI data are strongly correlated with terrestrial NPP and are frequently used as NPP predictors.
Abstract: Knapp and Smith (1) suggested that interannual variability in aboveground net primary production (ANPP) is not related to fluctuations in precipitation, based on analysis of data from 11 Long-Term Ecological Research sites across North America. This finding, if applicable to other regions, is crucial to climate change research, because it may necessitate revisions of projections of ecosystem responses to climate change (2, 3). To examine the relationship between variability in net primary production (NPP) and precipitation at a broad scale, a longterm normalized difference vegetation index (NDVI) data set derived from the Advanced Very High Resolution Radiometer (AVHRR) of the National Oceanic and Atmospheric Administration (NOAA), coupled with a historical climate data set, should constitute a useful and powerful data source, because NDVI data are strongly correlated with terrestrial NPP and are frequently used as NPP predictors (4, 5). We used an annual mean NDVI data set over China to quantify temporal NPP variability relative to precipitation variation, and used coefficient of variation (CV) to express the magnitude of interannual variability in NDVI and precipitation. We then calculated CVs of these two variables for each pixel, with a resolution of 0.1° latitude by 0.1° longitude, for five biome groups across China—forest, grassland, desert, alpine vegetation, and cropland (6 )—using 1982 to 1999 NDVI and precipitation data compiled in China (7 ). We assumed that interannual variability in NDVI or NPP was related to temporal variability in precipitation if the correlation between CVs for NDVI or NPP and precipitation were identified as statistically significant. The CV value of NDVI for these five biome groups showed a large spatial variation, with a mean CV of 8.3% for the forest biome group, 10.4% for grasslands, 24.6% for desert areas, 12.7% for alpine vegetation, and 9.3 % for cropland. The largest variation occurred in the desert bi

Journal ArticleDOI
TL;DR: The Climate System Model (CSM) as discussed by the authors is a coupled global climate model developed at the National Center for Atmospheric Research to simulate the twentieth-century climate using historical greenhouse gas and sulfate aerosol forcing, which was extended through the twenty-first century under two newly developed scenarios, a business-as-usual case (ACACIA-BAU, CO2 710 ppmv in 2100) and a CO2 stabilization case (STA550, CO 2 540 ppmvin 2100).
Abstract: The Climate System Model, a coupled global climate model without ‘‘flux adjustments’’ recently developed at the National Center for Atmospheric Research, was used to simulate the twentieth-century climate using historical greenhouse gas and sulfate aerosol forcing. This simulation was extended through the twenty-first century under two newly developed scenarios, a business-as-usual case (ACACIA-BAU, CO2 710 ppmv in 2100) and a CO2 stabilization case (STA550, CO 2 540 ppmv in 2100). Here we compare the simulated and observed twentieth-century climate, and then describe the simulated climates for the twenty-first century. The model simulates the spatial and temporal variations of the twentieth-century climate reasonably well. These include the rapid rise in global and zonal mean surface temperatures since the late 1970s, the precipitation increases over northern mid- and high-latitude land areas, ENSO-induced precipitation anomalies, and Pole‐ midlatitude oscillations (such as the North Atlantic oscillation) in sea level pressure fields. The model has a cold bias (28‐68C) in surface air temperature over land, overestimates of cloudiness (by 10%‐30%) over land, and underestimates of marine stratus clouds to the west of North and South America and Africa. The projected global surface warming from the 1990s to the 2090s is ;1.98C under the BAU scenario and ;1.58C under the STA550 scenario. In both cases, the midstratosphere cools due to the increase in CO 2, whereas the lower stratosphere warms in response to recovery of the ozone layer. As in other coupled models, the surface warming is largest at winter high latitudes ($5.08C from the 1990s to the 2090s) and smallest (;1.08C) over the southern oceans, and is larger over land areas than ocean areas. Globally averaged precipitation increases by ;3.5% (3.0%) from the 1990s to the 2090s in the BAU (STA550) case. In the BAU case, large precipitation increases (up to 50%) occur over northern mid- and high latitudes and over India and the Arabian Peninsula. Marked differences occur between the BAU and STA550 regional precipitation changes resulting from interdecadal variability. Surface evaporation increases at all latitudes except for 60 8‐908S. Water vapor from increased tropical evaporation is transported into mid- and high latitudes and returned to the surface through increased precipitation there. Changes in soil moisture content are small (within 63%). Total cloud cover changes little, although there is an upward shift of midlevel clouds. Surface diurnal temperature range decreases by about 0.28‐ 0.58C over most land areas. The 2‐8-day synoptic storm activity decreases (by up to 10%) at low latitudes and over midlatitude oceans, but increases over Eurasia and Canada. The cores of subtropical jets move slightly upand equatorward. Associated with reduced latitudinal temperature gradients over mid- and high latitudes, the wintertime Ferrel cell weakens (by 10%‐15%). The Hadley circulation also weakens (by ;10%), partly due to the upward shift of cloudiness that produces enhanced warming in the upper troposphere.

Journal ArticleDOI
TL;DR: It is shown that rain events are analogous to a variety of nonequilibrium relaxation processes in Nature such as earthquakes and avalanches and that power laws describe the number of rain events versus size and number of droughts versus duration.
Abstract: We show that rain events are analogous to a variety of nonequilibrium relaxation processes in Nature such as earthquakes and avalanches. Analysis of high-resolution rain data reveals that power laws describe the number of rain events versus size and number of droughts versus duration. In addition, the accumulated water column displays scale-less fluctuations. These statistical properties are the fingerprints of a self-organized critical process and may serve as a benchmark for models of precipitation and atmospheric processes.

01 Dec 2001
TL;DR: Johnson et al. as mentioned in this paper used multiple regression analysis of data from 10 sites within the Global Network for Isotopes in Precipitation (GNIP) to investigate the strength of these transfer functions in China.
Abstract: The stable isotopic composition of materials such as glacial ice, tree rings, lake sediments, and speleothems from low-to-mid latitudes contains information about past changes in temperature (T) and precipitation amount (P). However, the transfer functions which link NOp to changes in T or P, dNOp/dT and dNOp/dP, can exhibit significant temporal and spatial variability in these regions. In areas affected by the Southeast Asian monsoon, past variations in N18O and ND of precipitation have been attributed to variations in monsoon intensity, storm tracks, and/ or variations in temperature. Proper interpretation of past NOp variations here requires an understanding of these complicated stable isotope systematics. Since temperature and precipitation are positively correlated in China and have opposite effects on NOp, it is necessary to determine which of these effects is dominant for a specific region in order to perform even qualitative paleoclimate reconstructions. Here, we evaluate the value of the transfer functions in modern precipitation to more accurately interpret the paleorecord. The strength of these transfer functions in China is investigated using multiple regression analysis of data from 10 sites within the Global Network for Isotopes in Precipitation (GNIP). NOp is modeled as a function of both temperature and precipitation. The magnitude and signs of the transfer functions at any given site are closely related to the degree of summer monsoon influence. NOp values at sites with intense summer monsoon precipitation are more dependent on the amount of precipitation than on temperature, and therefore exhibit more negative values in the summer. In contrast, NOp values at sites that are unaffected by summer monsoon precipitation exhibit strong relationships between NOp and temperature. The sites that are near the northern limit of the summer monsoon exhibit dependence on both temperature and amount of precipitation. Comparison with simple linear models (NOp as a function of T or P) and a geographic model (NOp as a function of latitude and altitude) shows that the multiple regression model is more successful at reproducing NOp values at sites that are strongly influenced by the summer monsoon. The fact that the transfer function values are highly spatially variable and closely related to the degree of summer monsoon influence suggests that these values may also vary temporally. Since the Southeast Asian monsoon intensity is known to exhibit large variations on a number of timescales (annual to glacial^interglacial), and the magnitude and sign of the transfer functions is related to monsoon intensity, we suggest that as monsoon intensity changes, the magnitude and possibly even the sign of the transfer functions may vary. Therefore, quantitative paleoclimate reconstructions based on NOp variations may not 0012-821X / 04 / $ ^ see front matter < 2004 Elsevier B.V. All rights reserved. doi:10.1016/S0012-821X(04)00036-6 * Corresponding author. Tel. : +1-510-642-9539; Fax: +1-510-643-9980. E-mail address: kathleen@eps.berkeley.edu (K.R. Johnson). EPSL 6996 17-3-04 Earth and Planetary Science Letters 220 (2004) 365^377 R Available online at www.sciencedirect.com www.elsevier.com/locate/epsl be valid. < 2004 Elsevier B.V. All rights reserved.

Journal ArticleDOI
TL;DR: In this paper, the authors studied time variability of 10-day average volumetric soil moisture, collected at the tropical Andes of central Colombia at depths of 20 and 40 cm, in coffee growing areas characterized by shading vegetation ("shaded coffee"), forest, and sunlit coffee.
Abstract: An analysis of hydrologic variability in Colombia shows different seasonal effects associated with El Nino/Southern Oscillation (ENSO) phenomenon. Spectral and cross-correlation analyses are developed between climatic indices of the tropical Pacific Ocean and the annual cycle of Colombia's hydrology: precipitation, river flows, soil moisture, and the Normalized Difference Vegetation Index (NDVI). Our findings indicate stronger anomalies during December-February and weaker during March-May. The effects of ENSO are stronger for streamflow than for precipitation, owing to concomitant effects on soil moisture and evapotranspiration. We studied time variability of 10-day average volumetric soil moisture, collected at the tropical Andes of central Colombia at depths of 20 and 40 cm, in coffee growing areas characterized by shading vegetation ("shaded coffee"), forest, and sunlit coffee. The annual and interannual variability of soil moisture are highly intertwined for the period 1997-1999, during strong El Nino and La Nina events. Soil moisture exhibited greater negative anomalies during 1997-1998 El Nino, being strongest during the two dry seasons that normally occur in central Colombia. Soil moisture deficits were more drastic at zones covered by sunlit coffee than at those covered by forest and shaded coffee. Soil moisture responds to wetter than normal precipitation conditions during La Nina 1998 -1999, reaching maximum levels throughout that period. The probability density function of soil moisture records is highly skewed and exhibits different kinds of multimodality depending upon land cover type. NDVI exhibits strong negative anomalies throughout the year during El Ninos, in particular during September-November (year 0) and June-August (year 0). The strong negative relation between NDVI and El Nino has enormous implications for carbon, water, and energy budgets over the region, including the tropical Andes and Amazon River basin.

Journal ArticleDOI
TL;DR: The potential effects of global warming on the hydrology of 23 major rivers are investigated in this article, where changes in the climatology of precipitation, evapotranspiration, and soil moisture lead also to changes in runoff and streamflow.
Abstract: Changes in the climatology of precipitation, evapotranspiration, and soil moisture lead also to changes in runoff and streamflow. The potential effects of global warming on the hydrology of 23 major rivers are investigated. The runoff simulated by the Canadian Centre for Climate Modeling and Analysis (CCCma) coupled climate model for the current climate is routed through the river system to the river mouth and compared with results for the warmer climate simulated to occur towards the end of the century. Changes in mean discharge, in the amplitude and phase of the annual streamflow cycle, in the annual maximum discharge (the flood) and its standard deviation, and in flow duration curves are all examined. Changes in flood magnitudes for different return periods are estimated using extreme value analysis. In the warmer climate, there is a general decrease in runoff and 15 out of the 23 rivers considered experience a reduction in annual mean discharge (with a median reduction of 32%). The changes in runoff are not uniform and discharge increases for 8 rivers (with a median increase of 13%). Middle- and high-latitude rivers typically show marked changes in the amplitude and phase of their annual cycle associated with a decrease in snowfall and an earlier spring melt in the warmer climate. Low-latitude rivers exhibit changes in mean discharge but modest changes in their annual cycle. The analysis of annual flood magnitudes show that 17 out of 23 rivers experience a reduction in mean annual flood (a median reduction of 20%). Changes in flow duration curves are used to characterize the different kinds of behavior exhibited by different groups of rivers. Differences in the regional distribution of simulated precipitation and runoff for the control simulation currently limit the application of the approach. The inferred hydrological changes are, nevertheless, plausible and consistent responses to simulated changes in precipitation and evapotranspiration and indicate the kinds of hydrological changes that could occur in a warmer climate.

Journal ArticleDOI
TL;DR: In this paper, a new daily precipitation dataset, for the period 1920-1998, comprising seven stations located in the northeastern Italy, is presented, and a study aimed at investigating precipitation intensity and extreme events has been performed.
Abstract: A new daily precipitation dataset, for the period 1920–1998, comprising seven stations located in the northeastern Italy is presented. Seasonal and annual precipitation and number of rainy days have been analysed and a study aimed at investigating precipitation intensity and extreme events has been performed. Precipitation intensity has been analysed through studying both the mean precipitation amount per wet day and dividing precipitation into heavy and non-heavy classes. In addition, the return period of the extreme events has been calculated for 30-year running windows and its variations have been examined. The results show a negative trend in the number of wet days associated with an increase in the contribution of heavy rainfall events to total precipitation. This is in agreement with a reduction in return period for extreme events since 1920. Copyright © 2001 Royal Meteorological Society

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TL;DR: In this article, the authors examined the spatial and temporal characteristics of heavy precipitation events over Canada (excluding the high Arctic) for the period 1900-98, examining the 90th percentiles of daily precipitation, the annual maximum daily value, and the 20-yr return values.
Abstract: Spatial and temporal characteristics of heavy precipitation events over Canada (excluding the high Arctic) are examined for the period 1900–98. In southern Canada, about 71% of total precipitation comes from rainfall events. In northern Canada, more than 50% of total precipitation comes from snowfall events. Heavy rainfall and snowfall events are thus defined for each season and station separately by identifying a threshold value that is exceeded by an average of three events per year. Annual and seasonal time series of heavy event frequency are then obtained by counting the number of exceedances per year. Characteristics of the intensity of heavy precipitation events are investigated examining the 90th percentiles of daily precipitation, the annual maximum daily value, and the 20-yr return values. It was found that decadal variability is the dominant feature in both the frequency and the intensity of extreme precipitation events over the country. For the country as a whole, there appear to be no...

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TL;DR: In this paper, ensembles of seasonal simulations (March-September) have been performed in order to investigate the sensitivity of the Asian and African monsoon rainfall to regional soil moisture anomalies.
Abstract: Soil moisture responds to precipitation variability but also affects precipitation through evaporation. This two-way interaction has often been referred to as a positive feedback, since the water added to the land surface during a precipitation event leads to increased evaporation, and this in turn can lead to further rainfall. Various numerical experiments have suggested that this feedback has a major influence on tropical climate variability from the synoptic to the interannual timescale. In the present study, ensembles of seasonal simulations (March–September) have been performed in order to investigate the sensitivity of the Asian and African monsoon rainfall to regional soil moisture anomalies. After a control experiment with free-running soil moisture, other ensembles have been performed in which the soil water content is strongly constrained over a limited area, either south Asia or Sudan–Sahel. Besides idealized simulations in which soil moisture is limited by the value at the wilting poi...

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TL;DR: In this article, a daily survey highlights the impact of the origins and trajectories of air masses on the amount and the oxygen-18 content of rainfalls: enriched and higher amount Mediterranean precipitation, depleted and lower amount Atlantic precipitation.
Abstract: Environmental isotopes (18O, ²H) have been measured, between March 1997 and March 1999, at 10 stations located in the Mediterranean seaside countries (2 in Spain, 1 in Tunisia, 7 in France). Data collected on monthly, event and fractionated basis allow to understand the modifications of the isotopic content of precipitation due to meteorological phenomena. A monthly monitoring shows that the Western Mediterranean has a unique isotopic characteristic that is between Atlantic and Eastern Mediterranean. A daily survey highlights the impact of the origins and trajectories of air masses on the amount and the oxygen-18 content of rainfalls: enriched and higher amount Mediterranean precipitation, depleted and lower amount Atlantic precipitation. At last, fractionated sampling of heavy precipitation allows to establish a typology of the variations of the isotopic composition during a rain event.

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TL;DR: A new version of a global coupled atmosphere-ocean general circulation model (MRI-CGCM2) has been developed at the Meteorological Research Institute (MRI). The model can be used to explore climate change associated with anthropogenic forcings as discussed by the authors.
Abstract: A new version of a global coupled atmosphere-ocean general circulation model (MRI-CGCM2) has been developed at the Meteorological Research Institute (MRI). The model can be used to explore climate change associated with anthropogenic forcings. We aimed to reduce the drawbacks of the former version of the model (MRI-CGCM1, Tokioka. et. al., 1996) and achieve a more realistic climatic mean and variability to predict climate changes with greater accuracy. In a preliminary analysis of the control run, the model showed generally good performance in reproducing the mean climate (including seasonal variation) in representative aspects; surface air temperature, precipitation, snow and sea ice distribution, and ocean structure and circulation. The model is capable of making a stable integration longer than 200 years. The sea ice distribution is much improved and is close to the observed extent and thickness. The model simulates realistic strength of meridional overturning in the Atlantic Ocean that MRI-CGCM1 failed to simulate. The model realistically simulates variabilities such as Arctic Oscillation (AO) and ENSO. Temporal variation of the sea surface temperature (SST) anomaly in the NINO3 region (150°W to 90°W, 4°S to 4°N) shows a large positive value (max. +4°C) with several years interval. The SST anomaly pattern is similar to the observed El Nino with a strong positive anomaly in the central-eastern equatorial Pacific. The model still has some biases at present. The surface air temperature in winter at high latitude has a warm bias due to weaker stability in the boundary layer. The surface temperature over land in summer also shows a warm bias associated with a problem concerning the hydrological process.