Increasing Trend Of Precipitation Research Articles

Effects of Black Carbon Aerosols on the Indian Monsoon

Abstract A six-member ensemble of twentieth-century simulations with changes to only time-evolving global distributions of black carbon aerosols in a global coupled climate model is analyzed to study the effects of black carbon (BC) aerosols on the Indian monsoon. The BC aerosols act to increase lower-tropospheric heating over South Asia and reduce the amount of solar radiation reaching the surface during the dry season, as noted in previous studies. The increased meridional tropospheric temperature gradient in the premonsoon months of March–April–May (MAM), particularly between the elevated heat source of the Tibetan Plateau and areas to the south, contributes to enhanced precipitation over India in those months. With the onset of the monsoon, the reduced surface temperatures in the Bay of Bengal, Arabian Sea, and over India that extend to the Himalayas act to reduce monsoon rainfall over India itself, with some small increases over the Tibetan Plateau. Precipitation over China generally decreases due to the BC aerosol effects. There is a weakened latitudinal SST gradient resulting from BC aerosols in the model simulations as seen in the observations, and this is present in the multiple-forcings experiments with the Community Climate System Model, version 3 (CCSM3), which includes natural and anthropogenic forcings (including BC aerosols). The BC aerosols and consequent weakened latitudinal SST gradient in those experiments are associated with increased precipitation during MAM in northern India and over the Tibetan Plateau, with some decreased precipitation over southwest India, the Bay of Bengal, Burma, Thailand, and Malaysia, as seen in observations. During the summer monsoon season, the model experiments show that BC aerosols have likely contributed to observed decreasing precipitation trends over parts of India, Bangladesh, Burma, and Thailand. Analysis of single ensemble members from the multiple-forcings experiment suggests that the observed increasing precipitation trends over southern China appear to be associated with natural variability connected to surface temperature changes in the northwest Pacific.

Trends in Total Precipitation and Frequency of Daily Precipitation Extremes over China

Abstract Based on a newly developed daily precipitation dataset of 740 stations in China and more robust trend detection techniques, trends in annual and seasonal total precipitation and in extreme daily precipitation, defined as those larger than its 95th percentile for the year, summer, and winter half years, have been assessed for the period 1951–2000. Possible links between changes in total precipitation and frequency of extremes have also been explored. The results indicate that there is little trend in total precipitation for China as a whole, but there are distinctive regional and seasonal patterns of trends. Annual total precipitation has significantly decreased over southern northeast China, north China, and over the Sichuan Basin but significantly increased in western China, the Yangtze River valley, and the southeastern coast. In western China, precipitation increase has been observed for both cold and warm seasons. However, trends differ from one season to another in eastern China. Spring precipitation has increased in southern northeast China and north China but decreased significantly in the midreach of the Yangzte River. The summer precipitation trend is very similar to that of annual totals. Autumn precipitation has generally decreased throughout eastern China. In winter, precipitation has significantly decreased over the northern part of eastern China but increased in the south. The number of rain days has significantly decreased throughout most parts of China with northwest China being an exception. Meanwhile, precipitation intensity has significantly increased. This suggests that the precipitation increase in western China is due to the increase in both precipitation frequency and intensity. In eastern China, the impact of reduced number of rain days seems to be more dominant in the north while the influence of enhanced intensity prevails in the south. Over regions with increasing precipitation trends, there have been much higher than normal frequency of precipitation extreme events. For example, significant increases in extreme precipitation have been found in western China, in the mid–lower reaches of the Yangtze River, and in parts of the southwest and south China coastal area. A significant decrease in extremes is observed in north China and the Sichuan Basin. Trends in the number of extremes and total precipitation from nonextreme events are generally in phase. An exception is southwest China where an increase of extreme events is associated with a decrease in total nonextreme precipitation.

Spring precipitation variations over the western Himalaya, India, since A.D. 1731 as deduced from tree rings

Spring precipitation, representative of regional‐scale features, was reconstructed since A.D. 1731 using 15 site ring width chronologies of Himalayan cedar (Cedrus deodara (Roxb. ex Lambert) G. Don), prepared from distantly located moisture‐stressed sites in the western Himalayan region. This is so far the strongest tree‐ring‐based precipitation reconstruction in terms of variance explained in the calibration model (A.D. 1897–1986) from the western Himalayan region. The twentieth century experienced the driest and wettest years in the whole reconstructed series. The 10‐ and 20‐year means also indicate extreme precipitation periods in the twentieth century. The increasing precipitation trend noticed in the reconstructed data of the late twentieth century closely matches with instrumental data.

Trends in indices for extremes in daily temperature and precipitation in central and western Europe, 1901-99

We analyse 20th century trends in six indices for precipitation extremes and four indices for temperature extremes, calculated from daily observational data for European stations. The indices chosen reflect rather moderate extremes. Most of the ~80 stations used are situated in central and western Europe; therefore, results mainly refer to this region. Trends are calculated over 1901-99, 1921-99, 1901-50 and 1946-99. Two different trend estimators are used, and significance is assessed with a bootstrap technique. We find that: • Significant incr easing precipitation trends over the 20th century dominate in winter for both average precipitation intensity and moderately strong events. Simultaneously, the length of dry spells generally increased insignificantly. • There are few significant trends of any sign for precipitation indices in summer, but there are insignificant drying trends over Scandinavia and wetting trends over central and western Europe for 1921-99. The length of dry spells in summer generally increased insignificantly. • Both the warm and cold tails of the temperature distribution in winter warmed over the entire 20th century. Notably low values in the cold tail for daily Tmax and Tmin occurred in the early 1940s, leading to strong but insignificant negative trends for 1901-50, whereas little change occurred before 1940. • Warming of winters during 1946-99 occurred in both the warm and cold tails for both Tmax and Tmin, with the largest warming in the cold tail for Tmin. • The warm tail of daily Tmin (and to a smaller extent Tmax) in summer warmed significantly during the past century. There is more evidence for summer warming in the first half of the century compared with the second half. • During 1946-99, the warm tail of daily Tmax in summer was generally warming while the cold tail was cooling (both insignificantly). • More digitized daily observational data from various European sub-regions are needed to permit a spatially more extensive analysis of changes in climate extremes over the last century.

Wavelet analysis of precipitation variability in northern California, U.S.A.

Precipitation temporal variability on 96 years is studied by the application of the wavelet transform to five precipitation series at locations in northern California, U.S.A. The wavelet transform spectra are computed for annual total precipitation and wetseas on precipitation of each record. Comparing two results based on annual and wet season data, all components appear seasonally dependent. Meanwhile, monotonic trends estimated by wavelet transform indicate wetting in the northern California precipitation data. According to the wavelet analysis, the spatial pattern of the precipitation field may have been changed since 1945, and the dominant period is about 16 years. In addition, the recent increasing precipitation trend in northern California can be interpreted as the coupled effect of the extremely long-period component and multi-decadal period components.

The forecast of seasonal precipitation trend at the north Helan Mountain and Baiyinaobao regions, Inner Mongolia for the next 20 years

By using Caterpillar-SSA analysis method, through the process of embedding, singular value decomposition, grouping and diagonal averaging, the seasonal precipitation trend at north Helan Mountain and Baiyinaobo regions, Inner Mongolia for the next 20 years is forecasted. The results show an increasing precipitation trend from 1992 to 2004. In the subsequent decade the precipitation should reduce quickly, and it will reach a minimum near 2012 to 2014 in both regions. The drought caused by the decrease of the precipitation from May to July in the north Helan Mountain area during the period of 2013–2014 is probably quite similar to that around 1929. Further, the period of precipitation gradual increase follows in the researched regions.

A multi-proxy holocene record of environmental change fromthe sediments of Skinny Lake, Iskut region, northern British Columbia,Canada

A stratigraphic record from a lake in the Central Plateau Regionof northern British Columbia reveals changes in environment and inferredclimate during the Holocene. Upon deglaciation (ca. 11500 BP), Skinny Lakebecame an embayment of an ice-dammed lake. High clastic sedimentationrates, an unstable landscape, and cool, possibly wet conditions likelypersisted until the early Holocene (ca. 9000 BP). From ca. 9000–8300 BPdeclining lake levels coupled with warm and dry conditions resulted in theformation of a prominent marl bed. A colonizing shrub and herb assemblagepersisted from 9000 BP until about 8300 BP when it was replaced by a spruce(Picea) and subalpine fir (Abieslasiocarpa) forest under slightly cooler and moister conditions. Themiddle Holocene was warmer-than-present, however, decreasingtemperature and increasing precipitation trends characterize the period fromca. 6000 BP–3000 BP. The transition to modern climate at 3000 BP isevident primarily in the lithostratigraphic record and corresponds with theinitiation of the Tiedemann glacial advance (ca. 3300 BP) in thesouth-coastal mountains of British Columbia. A significant change infossil pollen occurs at ca. 2400 BP and is characterised by an increase in pinepollen accompanied by decreases in alder (Alnus), spruceand fir. This also coincides with an increase in west-sourced exoticwestern hemlock (Tsuga heterophylla) and cedar type(Cupressaceae) pollen possibly transported by regional changes in air masscirculation patterns associated with Aleutian Low dynamics. This studydemonstrates that both lithostratigraphic and biotic proxies are helpful inreconstructing the timing and nature of climate change and that each may havevarying sensitivities to a particular type of change.

Variation of spatial annual precipitation sums in central europe in the period 1881‐1980

AbstractThe analysis of atmospheric precipitation variation in Central Europe in the period 1881‐1980 is based on the series of the so‐called spatial annual precipitation sums for the F.R.G., the G.D.R., Poland, Bohemia, Moravia, Slovakia and Hungary and for the Baur series. The annual precipitation variation in the above period is studied by means of series of 5‐year and 11‐year gliding means. Methods of autocorrelation analysis, spectral analysis (partly according to Blackman and Tukey, partly maximum entropy spectral analysis), coherency analysis and numerical bandpass filtering were used for analysing precipitation periodicities and cycles.In the period studied, the western part of Central Europe (the Baur series, F.R.G., also G.D.R.) shows a generally increasing precipitation trend at below‐mean sums approximately up to 1920, whereas a more or less decreasing tendency is typical of the remaining series. Periods with analogous lengths appear in precipitation series in the whole of Central Europe and at the same time the lengths of significant periods are shortened from 4.4 and 5.0a (a = year) in the western part to 3.3 and 3.6a in the eastern part. At the same time, significant coherence among the studied series most frequently appears for periods of 2.5 and 13.3a. Periods with lengths of 2‐3 years take a more conspicuous part in the total variance of the corresponding series (about 30 per cent), except in the cases of Slovakia and Hungary, where the maximum share is shifted to oscillations with periods of 3‐4 years and for the F.R.G. and the Baur series to the interval of 4‐6 years. The course of the filtered series refers to the length and phase instability of the periodicities found, which complicates the use of the knowledge obtained for long‐term precipitation forecasting.