Increase In Mean Precipitation Research Articles

Regional climate change scenarios and their impacts on water requirements for wheat production in Iran

We simulate the effect of climate change on water requirements of cold season wheat in various climatic zones of Iran. The research considers both observed climate (temperature and precipitation) changes during recent decades (1960-2009) based on instrumental records and projected future changes to 2100 based on the MAGICC/SCENGEN 5.3 compound model. 20 General Circulation models are used based on a single scenario known as P50, which is the average of SRES or emission scenarios. Results indicate that whilst winter precipitation has marginally increased across the country as a whole, a significant decline in mean spring precipitation is recorded between 1960 and 2009. However, considerable variability in trends is measured across various climatic regions of Iran. Mean annual temperature / rainfall changes in the various climate zones of Iran for the period 1960-2009 follow: +0.1 ° C / decade / +0.43 mm / decade in arid regions, -0.1 ° C / decade / -1.7 mm / decade in semi-arid regions, +0.1 ° C / decade / -1.33 mm / decade in Mediterranean / semihumid regions and -0.01 ° C / decade / -0.04 mm / decade in humid / hyper humid regions. Temperature projections to 2100 indicate an overall temperature rise of ca. 4.25 ˚C relative to that for 1961-1990, with increases projected for all climatic regions of Iran. Despite an overall projected mean precipitation increase of 36% for the year 2100, relative to that for 1961-1990, these are insufficient to compensate for temperature increases. Consequently, calculated water deficits during the growing season (autumn to spring) in Iran’s wheat producing areas are expected to increase from 5.2% in 1980 to over 23% by 2050 and 38% by 2100.

Sensitivity of mean annual primary production to precipitation

AbstractIn many terrestrial ecosystems, variation in aboveground net primary production (ANPP) is positively correlated with variation in interannual precipitation. Global climate change will alter both the mean and the variance of annual precipitation, but the relative impact of these changes in precipitation on mean ANPP remains uncertain. At any given site, the slope of the precipitation‐ANPP relationship determines the sensitivity of mean ANPP to changes in mean precipitation, whereas the curvature of the precipitation‐ANPP relationship determines the sensitivity of ANPP to changes in precipitation variability. We used 58 existing long‐term data sets to characterize precipitation‐ANPP relationships in terrestrial ecosystems and to quantify the sensitivity of mean ANPP to the mean and variance of annual precipitation. We found that most study sites have a nonlinear, saturating relationship between precipitation and ANPP, but these nonlinearities were not strong. As a result of these weak nonlinearities, ANPP was nearly 40 times more sensitive to precipitation mean than variance. A 1% increase in mean precipitation caused a −0.2% to 1.8% change in mean ANPP, with a 0.64% increase on average. Sensitivities to precipitation mean peaked at sites with a mean annual precipitation near 500 mm. Changes in species composition and increased intra‐annual precipitation variability could lead to larger ANPP responses to altered precipitation regimes than predicted by our analysis.

El Niño-Southern Oscillation sensitivity to cumulus entrainment in a coupled general circulation model

Received 6 July 2011; revised 26 August 2011; accepted 14 September 2011; published 22 November 2011. [1] A series of 200 year long integrations is performed using the Geophysical Fluid Dynamics Laboratory CM2.1 by varying the Tokioka parameter, a minimum entrainment rate threshold in the cumulus parameterization. Changing the threshold alters both the tropical Pacific mean state and the El Nino–Southern Oscillation (ENSO) variability. Increasing the Tokioka parameter causes a basin‐wide cooling in the tropical Pacific with the reduction of high clouds. The degree of cooling in the western part of the basin is bigger than that in the east. As a result, the east–west asymmetry in the tropical Pacific sea surface temperature (SST) decreases with increasing the Tokioka parameter. Accompanied with the reduced east–west SST asymmetry are the increase of mean precipitation over the eastern Pacific and the eastward shift of the atmospheric responses to the ENSO‐related SST forcing. The eastward shifted wind stress anomaly associated with ENSO leads to the stronger ENSO variability. In this way the magnitude of ENSO simulated in this model increases with the Tokioka parameter. Implication of our results on the relationship between the tropical Pacific mean state and ENSO is discussed.

Precipitation Regulates the Response of Net Ecosystem CO2 Exchange to Environmental Variation on United States Rangelands

Rangelands occupy 50% of Earth’s land surface and thus are important in the terrestrial carbon (C) cycle. For rangelands and other terrestrial ecosystems, the balance between photosynthetic uptake of carbon dioxide (CO2) and CO2 loss to respiration varies among years in response to interannual variation in the environment. Variability in CO2 exchange results from interannual differences in 1) environmental variables at a given point in the annual cycle (direct effects of the environment) and in 2) the response of fluxes to a given change in the environment because of interannual changes in biological factors that regulate photosynthesis and respiration (functional change). Functional change is calculated as the contribution of among-year differences in slopes of flux-environment relationships to the total variance in fluxes explained by the environment. Functional change complicates environmental-based predictions of CO2 exchange, yet its causes and contribution to flux variability remain poorly defined. We determine contributions of functional change and direct effects of the environment to interannual variation in net ecosystem exchange of CO2 (NEE) of eight rangeland ecosystems in the western United States (58 site-years of data). We predicted that 1) functional change is correlated with interannual change in precipitation on each rangeland and 2) the contribution of functional change to variance in NEE increases among rangelands as mean precipitation increases. Functional change explained 10–40% of the variance in NEE and accounted for more than twice the variance in fluxes of direct effects of environmental variability for six of the eight ecosystems. Functional change was associated with interannual variation in precipitation on most rangelands but, contrary to prediction, contributed proportionally more to variance in NEE on arid than more mesic ecosystems. Results indicate that we must account for the influence of precipitation on flux-environment relationships if we are to distinguish environmental from management effects on rangeland C balance.

Changes in the Global Sulfate Burden due to Perturbations in Global CO2 Concentrations

Abstract A large ensemble of general circulation model (GCM) integrations coupled to a fully interactive sulfur cycle scheme were run on the climateprediction.net platform to investigate the uncertainty in the climate response to sulfate aerosol and carbon dioxide (CO2) forcing. The sulfate burden within the model (and the atmosphere) depends on the balance between formation processes and deposition (wet and dry). The wet removal processes for sulfate aerosol are much faster than dry removal and so any changes in atmospheric circulation, cloud cover, and precipitation will feed back on the sulfate burden. When CO2 is doubled in the Hadley Centre Slab Ocean Model (HadSM3), global mean precipitation increased by 5%; however, the global mean sulfate burden increased by 10%. Despite the global mean increase in precipitation, there were large areas of the model showing decreases in precipitation (and cloud cover) in the Northern Hemisphere during June–August, which reduced wet deposition and allowed the sulfate burden to increase. Further experiments were also undertaken with and without doubling CO2 while including a future anthropogenic sulfur emissions scenario. Doubling CO2 further enhanced the increases in sulfate burden associated with increased anthropogenic sulfur emissions as observed in the doubled CO2-only experiment. The implications are that the climate response to doubling CO2 can influence the amount of sulfate within the atmosphere and, despite increases in global mean precipitation, may act to increase it.

Trends in heavy precipitation in the Czech Republic over 1961–2005

AbstractTrends in multiple characteristics of heavy precipitation over the area of the Czech Republic are evaluated using a new dataset from 175 rain‐gauge stations covering the period 1961–2005. The temporal changes are generally more pronounced in the western than eastern part of the country. Spatially coherent increasing trends are identified for all indices of heavy precipitation in winter in the western region, the relative trend magnitudes being mostly between 20 and 30% over the 45 years. Increasing but insignificant and spatially less coherent trends in heavy precipitation prevail also in summer. Opposite trends occur in spring (when they are related to declines in seasonal precipitation totals), and the changes are spatially least coherent and insignificant in autumn (in spite of the increase in mean precipitation). The differences between winter and summer on the one hand and the transition seasons on the other highlight the need for involving spring and autumn into studies of temporal changes of climatic variables, to avoid simplified views. It is also shown that trends in heavy precipitation at Prague‐Klementinum, the most frequently analysed long‐term station in the Czech Republic [and the only one available in continental‐scale analyses within the European Climate Assessment (ECA) project and related activities], are particularly unrepresentative for a wider area. The analysis partly supports an emerging global picture of prevailing positive trends in precipitation extremes over the mid‐latitudinal land areas of the Northern Hemisphere in winter. However, the cut‐off between the western and eastern parts of the Czech Republic in many precipitation characteristics, including the trends in wintertime indices of precipitation extremes, may indicate that the pattern of changes is more complex and less coherent in eastern than in western Europe. Copyright © 2008 Royal Meteorological Society

How Much Will Precipitation Increase With Global Warming?

The advent of meteorological satellites during the 1970s made possible the observation of the seasonally shifting patterns of global precipitation. It was not until recently, however, that the record could be considered long enough to investigate longer‐term trends and the relationship between global precipitation and global warming. Using data from the Special Sensor Microwave Imager (SSM/I) instrument, Wentz et al. [2007] reported that global mean precipitation increased at a rate of 7.4±2.6% per °C between 1987 and 2006.Meanwhile, general circulation models (GCMs) used to predict climate change simulate twentieth‐ and 21st‐century mean precipitation increases of about 13% per °C [Held and Soden, 2006]. This difference seems surprising because some GCMs can adequately reproduce the much longer twentieth‐ century surface‐based land‐mean precipitation record [Lambert et al., 2005]. Global precipitation changes are tied to the surface energy budget through evaporation and to the tropospheric energy budget through condensation. Thus, if GCMs do underestimate global precipitation changes, the simulation of other climate variables will be affected.

Changes in Mean and Extreme Precipitation in Near-term Predictions up to the Year 2030

We show the near-term predictions of mean and extreme precipitation up to the year 2030 by analyzing ten-member ensemble runs with perturbed initial conditions of the MIROC model. Mean and extreme precipitation increase in high latitudes and the tropics, and decrease in the subtropics in the ensemble mean. Uncertainty due to natural variability was also examined. Most of the ten runs predict positive anomalies in high latitudes and some parts of the tropics. Changes in parts of the subtropics are uncertain due to natural variability. Thermodynamic changes mainly explain robust total increases in mean precipitation in high latitudes and the tropics. Thermodynamic changes of mean precipitation are uncertain in the subtropics, resulting in a large uncertainty in total changes. It is suggested that small signal-to-noise rations of thermodynamic changes in the subtropics are induced by regional decreases in relative humidity at lower troposphere, which counteract the effects of increased column-integrated water vapor.

Changes in drought frequency, severity and duration for the British Isles projected by the PRUDENCE regional climate models

Summary Using multiple climate models for impact assessment allows the examination of uncertainty in projections of change, thus providing improved tools for the adaptation and mitigation of the impacts of future change. Here, the performance of integrations from six regional climate models (RCMs) driven by four different general circulation models (GCMs) have been assessed for British Isles mean precipitation and drought statistics for the 1961–1990 period, using two drought severity indices based on monthly precipitation anomalies. Spatially averaged statistics are examined in addition to spatial variations in model performance over water resource regions and compared with observations. Estimates of the range and sources of uncertainty in future changes are examined for the SRES A2 2071–2100 emissions scenario. Results indicate that the RCMs are able to reproduce the spatially averaged annual precipitation cycle over the British Isles but the spatial anomalies suggest that they may have difficulty in capturing important physical processes responsible for precipitation. The RCMs are unable to simulate the observed frequency of drought events in their control climate, particularly for severe events, possibly due to a failure to simulate persistent low precipitation. Future projections suggest an increase in mean precipitation in winter and decrease in summer months. Short-term summer drought is projected to increase in most water resource regions except Scotland and Northern Ireland, although the uncertainty associated with such changes is large. Projected changes in longer droughts are influenced by the driving GCM and are highly uncertain, particularly for the south of England, although the longest droughts are projected to become shorter and less severe by most models. This suggests that many water supply companies may need to plan for more intense short-term droughts but may experience fewer longer duration events under future climate change.

Evidence of urban-induced precipitation variability in arid climate regimes

The study employs a 108-year precipitation historical data record, global climate observing network observations and satellite data to identify possible anomalies in rainfall in and around two major arid urban areas, Phoenix, Arizona and Riyadh, Saudi Arabia. The analysis reveals that during the monsoon season, locations in northeastern suburbs and exurbs of the Phoenix metropolitan area have experienced statistically significant increases in mean precipitation of 12–14% from a pre-urban (1895–1949) to post-urban (1950–2003) period. Further analysis of satellite-based rainfall rates suggests the existence of the anomaly region (AR) over a 7-year period. The anomaly cannot simply be attributed to maximum topographic relief and is hypothesized to be related to urban-topographic interactions and possibly irrigation moisture. Temperature records suggest that Riyadh has experienced an adjustment in mean temperature in response to the growth of urban surfaces (e.g. the so-called urban heat island effect). While ground-based precipitation records also indicate an upward trend in mean and total precipitation in and around Riyadh in the last 10–15 years, it is difficult to attribute the increase to urbanization because other less urbanized stations in Saudi Arabia also show a similar increase. Recent satellite-based precipitation estimates indicate an AR 50–100 km north of Riyadh, but this study is not robust enough to conclusively link it to urbanization although certain climate-regime attributes suggests that it might be.

Dynamic and thermodynamic influences on intensified daily rainfall during the Asian summer monsoon under doubled atmospheric CO2 conditions

Results from time‐slice ensemble experiments using a T106 AGCM revealed changes in the South Asian summer monsoon resulting from climate change. Model results under global warming conditions suggested more warming over land than over the ocean, a northward shift of lower tropospheric monsoon circulation, and an increase in mean precipitation during the Asian summer monsoon. The number of extreme daily precipitation events increased significantly. Increases in mean and extreme precipitation were attributed to greater atmospheric moisture content (a thermodynamic change). In contrast, dynamic changes limited the intensification of mean precipitation. Enhanced extreme precipitation over land in South Asia arose from dynamic changes rather than thermodynamic changes.

ASIAN SUMMER MONSOON UNDER THE GLOBAL WARMING USING A HIGH-RESOLUTION ATMOSPHERIC GENERAL CIRCULATION MODEL

Results from time-slice ensemble experiments using a T106 AGCM revealed changes in the South Asian summer monsoon resulting from climate change. Model results under global warming conditions, which are consistent with previous studies, suggested more warming over land than over the ocean, a northward shift of lower tropospheric monsoon circulation, and an increase in mean precipitation during the Asian summer monsoon. The number of extreme daily precipitation events increased significantly. Increases in mean and extreme precipitation were attributed to greater atmospheric moisture content (a thermodynamic change). In contrast, dynamic changes limited the intensification of mean precipitation. Enhanced extreme precipitation over land in South Asia arose from dynamic changes rather than thermodynamic changes.

Understanding future patterns of increased precipitation intensity in climate model simulations

In a future climate warmed by increased greenhouse gases, increases of precipitation intensity do not have a uniform spatial distribution. Here we analyze a multi‐model AOGCM data set to examine processes that produce the geographic pattern of these precipitation intensity changes over land. In the tropics, general increases in water vapor associated with positive SST anomalies in the warmer climate produce increased precipitation intensity over most land areas. In the midlatitudes, the pattern of precipitation intensity increase is related in part to the increased water vapor being carried to areas of mean moisture convergence to produce greater precipitation, as well as to changes in atmospheric circulation. Advective effects, indicated by sea level pressure changes, contribute to greatest precipitation intensity increases (as well as mean precipitation increases) over northwestern and northeastern North America, northern Europe, northern Asia, the east coast of Asia, southeastern Australia, and south‐central South America.

Impact of increasing CO2 on monthly-to-annual precipitation extremes: analysis of the CMIP2 experiments

The impact of increasing atmospheric CO2 on high and low extremes of monthly-to-annual precipitation is studied using 20 model experiments participating in the second phase of the coupled model intercomparison project (CMIP2). In marked contrast with previous research on daily precipitation extremes, the simulated changes in extremes on these longer time scales are well correlated with the changes in the long-term mean precipitation: wet extremes become more severe especially where the mean precipitation increases, and dry extremes where the mean precipitation decreases. Changes in relative variability play a smaller but discernible role. In an ensemble-mean sense, the variability increases slightly in most areas, so that the contrast between the high and low precipitation extremes grows larger with increasing CO2. The changes in the frequency of extremes (fraction of cases with precipitation above a high or below a low predefined threshold) are much larger than the changes in their magnitude. Most of the ensemble-averaged changes in the frequency of extremes can be reconstructed by using the changes in time mean precipitation alone, provided that the variation in time mean precipitation change between different models is taken into account. The nonlinear relationship between the mean precipitation and the frequency of extremes complicates the interpretation of the frequency changes, especially when averaging frequencies over different models.

A three-dimensional climate—ice-sheet model applied to the Last Glacial Maximum

A quasi-three-dimensional (3-D) climate model (Sellers, 1983) was used to simulate the climate of the Last Glacial Maximum (LGM) in order to provide climatic input for the modelling of the Northern Hemisphere ice sheets. The climate model is basically a coarse-gridded general circulation (GCM) with simplified dynamics, and was subject to appropriate boundary conditions for ice-sheet elevation, atmospheric CO2concentration and orbital parameters. When compared with the present-daysimulation, the simulated climate at the Last Glacial Maximum is characterized by a global annual cooling of 3.5°C and a reduction in global annualprecipitation of 7.5%, which agrees well with results from other, more complex GCMs. Also the patterns of temperature change compare fairly with mostother GCM results, except for a smaller cooling over the North Atlantic and the larger cooling predicted for the summer rather than for the winter over Eurasia.The climate model is able to simulate changes in Northern Hemisphere tropospheric circulation, yielding enhanced westerlies in the vicinity of the Laurentide and Eurasian ice sheets. However, the simulated precipitation patterns are less convincing, and show a distinct mean precipitation increase over the Laurentide ice sheet. Nevertheless, when using the mean-monthly fields of LGM minus present-day anomalies of temperature and precipitation rate to drive a three-dimensional thermomechanical ice-sheet model, it was demonstrated that within realistic bounds of the ice-flow and mass-balance parameters, veryreasonable reconstructions of the Last Glacial Maximum ice sheets could be obtained.

An Alternative Explanation of Rainfall Anomalies

Precipitation data from the Canadian prairies have been examined for the presence of persistent rainfall singularities. The meteor theory suggests that these might be caused by increases in concentration of efficient ice nuclei, originating from annual meteor shower occurrences during the preceding month. The present investigations have not tended to support this contention. There is no correlation apparent between the persistence, magnitude, or sharpness of a particular rainfall anomaly and the equivalent properties of the meteor influx presumed to cause it. Furthermore, although a number of peaks correspond, with 31 days delay time, to the mean dates of meteor showers, it is shown that, due to the nature of the rainfall pattern, other delay times can provide equally good apparent correlation between the two sets of events. This would indicate that the rainfall amounts are not truly influenced by periodic increases in the influx of meteoritic material. An alternative explanation for rainfall singularities is advanced which suggests that they are simply the result of day-to-day inhomogeneities in the long-term, average pressure pattern. Thus, low pressure areas would be, on the average, more prevalent or intense on certain days of the year than on others, and under such circumstances, an increase in mean precipitation could be expected. This proposed theory of persistent synoptic instability has been tested by a comparison of precipitation forecasts based on long-term mean pressure maps with actual precipitation amounts. While further critical tests are required, the results are promising, and there is indication that anomalies in mean temperature and cirrus cloud prevalence might be attributed to the same mechanism. The synoptic instability theory may thus provide a more satisfactory explanation of precipitation peaks, from the physical point of view at least, than does the meteor hypothesis.