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In this paper, the regional climate model REMO is used to investigate the added value of downscaling low resolutions global climate models (GCMs) and the climate change projections over Central Africa. REMO was forced by two GCMs (EC-Earth and MPI-ESM), for the period from 1950 to 2100 under the Representative Concentration Pathway 8.5 scenario. The performance of the REMO simulations for current climate is compared first with REMO simulation driven by ERA-Interim reanalysis, then by the corresponding GCMs in order to determine whether REMO outputs are able to effectively lead to added value at local scale. We found that REMO is generally able to better represent some aspects of the rainfall inter-annual variability, the daily rainfall intensity distribution as well as the intra-seasonal variability of the Central African monsoon, though few biases are still evident. It is also found that the boundary conditions strongly influences the spatial distribution of seasonal 2-m temperature and rainfall. From the analysis of the climate change signal from the present period 1976-2005 to the future 2066-2095, we found that all models project a warming at the end of the twenty-first century although the details of the climate change differ between REMO and the driving GCMs, specifically in REMO where we observe a general decrease in rainfall. This rainfall decrease is associated with delayed onset and anticipated recession of the Central African monsoon and a shortening of the rainy season. Small-scales variability of the climate change signal for 2-m temperature are usually smaller than that of the large-scales climate change part. For rainfall however, small-scales induce change of about 70% compared to the present climate statistics. [ABSTRACT FROM AUTHOR]

Investigations into the climatic forcings that affect the long-term variability of the Indian summer monsoon are constrained by a lack of reliable rainfall data prior to the late nineteenth century. Extensive qualitative and quantitative meteorological information for the pre-instrumental period exists within historical documents, although these materials have been largely unexplored. This paper presents the first reconstruction of monsoon variability using documentary sources, focussing on western India for the period 1781-1860. Three separate reconstructions are generated, for (1) Mumbai, (2) Pune and (3) the area of Gujarat bordering the Gulf of Khambat. A composite chronology is then produced from the three reconstructions, termed the Western India Monsoon Rainfall reconstruction (WIMR). The WIMR exhibits four periods of generally deficient monsoon rainfall (1780-1785, 1799-1806, 1830-1838 and 1845-1857) and three of above-normal rainfall (1788-1794, 1813-1828 and 1839-1844). The WIMR shows good correspondence with a dendroclimatic drought reconstruction for Kerala, although agreement with the western Indian portion of the tree-ring derived Monsoon Asia Drought Atlas is less strong. The reconstruction is used to examine the long-term relationship between the El Nino-Southern Oscillation (ENSO) and monsoon rainfall over western India. This exhibits peaks and troughs in correlation over time, suggesting a regular long-term fluctuation. This may be an internal oscillation in the ENSO-monsoon system or may be related to volcanic aerosol forcings. Further reconstructions of monsoon rainfall are necessary to validate this. The study highlights uncertainties in existing published rainfall records for 1817-1846 for western India. [ABSTRACT FROM AUTHOR]

In a climate change scenario, the present work deals with the possibility of the changes in the rainfall pattern during the principal monsoon season (June 1-September 30) of the Indian summer monsoon. For this purpose three attributes are defined as DTMR, DHMR and DNMR representing the day when 10, 50 and 90 % of the accumulated summer monsoon rainfall is achieved respectively. Using a high resolution (1° × 1°) gridded rainfall data set for the last 50 years prepared by India Meteorological Department (Rajeevan et al. , in Curr Sci 91:296-306, ), the analysis has been carried out over the different parts of the Indian subcontinent. Using statistically robust significance tests, it is observed that the distribution of the three variables have changed significantly at 1 % (or 5 %) significance level in the last 50-year of period. The DTMR and DNMR arrive 2 days early over central India, whereas DHMR appears to arrive 6 days early over west India in the recent decades. The results presented in this paper are supported by the statistically robust significance tests; suggest an apparent change in terms of the arrival of the rainfall attributes during the last half century. [ABSTRACT FROM AUTHOR]

The trend analysis approach is adopted for the prediction of future climatological behavior and climate change impact on agriculture, the environment, and water resources. In this study, the innovative trend pivot analysis method (ITPAM) and trend polygon star concept method were applied for precipitation trend detection at 11 stations located in the Soan River basin (SRB), Potohar region, Pakistan. Polygon graphics of total monthly precipitation data were created and trends length and slope were calculated separately for arithmetic mean and standard deviation. As a result, the innovative methods produced useful scientific information and helped in identifying, interpreting, and calculating monthly shifts under different trend behaviors, that is, increase in some stations and decrease in others of precipitation data. This increasing and decreasing variability emerges from climate change. The risk graphs of the total monthly precipitation and monthly polygonal trends appear to show changes in the trend of meteorological data in the Potohar region of Pakistan. The monsoonal rainfall of all stations shows a complex nature of behavior, and monthly distribution is uneven. There is a decreasing trend of rainfall in high land stations of SRB with a significant change between the first dataset and the second dataset in July and August. It was examined that monsoon rainfall is increasing in lowland stations indicating a shifting pattern of monsoonal rainfall from highland to lowland areas of SRB. The increasing and decreasing trends in different periods with evidence of seasonal variations may cause irregular behavior in the water resources and agricultural sectors. Significance Statement: The monthly polygonal trends with risk graphs of total monthly precipitation data depicted a clear picture of climate change effects in the Potohar region of Pakistan. The monsoonal rainfall showed a significant decreasing trend in highland stations and an increasing trend in lowland stations, indicating a shifting pattern of monsoonal rainfall from highland to lowland areas. [ABSTRACT FROM AUTHOR]

Climate on the Tibetan Plateau is often considered sensitive to global changes, yet the degree of sensitivity in different spaces and seasons prior to instrumental records is not clear. In this paper, we studied tree-ring maximum latewood density (MXD) to examine the late-summer (August–September) temperature variation over the past two and half centuries on the eastern Tibetan Plateau. The MXD regional chronology was established from 109 tree-ring samples of Balfour spruce [ Picea likiangensis var. balfouriana (Rehd. et Wils.)] at four high elevation sites. The chronology exhibited a high correlation ( r = 0.82, n = 56, p < 0.001) with the mean August–September temperature. Using the tree-ring data, we reconstructed the late-summer temperature for the period A.D. 1765–2009. The reconstruction accounted for 71.4% of the variance in instrumental temperature in the period 1954–2009. The reconstructed temperature did not show a warming trend in the past 250 years, suggesting a unique characteristic of late-summer temperature variability in the study region of the Tibetan Plateau. Our tree-ring data are useful for further understanding of the plateau's thermal condition in late summer and its role in regulating southward retreat of the Southwest Asian monsoon. [ABSTRACT FROM AUTHOR]

Interdependencies between the El Niño-Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and Indian monsoon (IM) phenomena are investigated from data over the period of 1871-2013. Along with the bivariate analysis of directional couplings between ENSO, NAO, and IM, their trivariate analysis was carried out. To detect the seasonal features of directional couplings using Wiener-Granger causality, various temporal resolutions of the data ranging from a month to a half-year are used. Taking into account the seasonality of the processes, the influence of ENSO on NAO is detected which has different signs in winter and summer. The influence of NAO on ENSO is revealed only in the trivariate analysis. The strongest couplings are observed between ENSO and IM. All the detected couplings can be divided into two groups: the "fast" (with the characteristic time from a month to several months) and "slow" (with the characteristic time of a half-year or longer) ones. The fast couplings include bidirectional couplings between IM and ENSO in summer and autumn when the summer pattern of NAO influences the patterns of ENSO and IM in the next season. The slow couplings include the effects of ENSO on NAO and on the winter pattern of IM as well as the influence of IM on the summer pattern NAO. [ABSTRACT FROM AUTHOR]

With the twentieth century analysis data (1901-2002) for atmospheric circulation, precipitation, Palmer drought severity index, and sea surface temperature (SST), we show that the Asian-Pacific Oscillation (APO) during boreal summer is a major mode of the earth climate variation linking to global atmospheric circulation and hydroclimate anomalies, especially the Northern Hemisphere (NH) summer land monsoon. Associated with a positive APO phase are the warm troposphere over the Eurasian land and the relatively cool troposphere over the North Pacific, the North Atlantic, and the Indian Ocean. Such an amplified land-ocean thermal contrast between the Eurasian land and its adjacent oceans signifies a stronger than normal NH summer monsoon, with the strengthened southerly or southwesterly monsoon prevailing over tropical Africa, South Asia, and East Asia. A positive APO implies an enhanced summer monsoon rainfall over all major NH land monsoon regions: West Africa, South Asia, East Asia, and Mexico. Thus, APO is a sensible measure of the NH land monsoon rainfall intensity. Meanwhile, reduced precipitation appears over the arid and semiarid regions of northern Africa, the Middle East, and West Asia, manifesting the monsoon-desert coupling. On the other hand, surrounded by the cool troposphere over the North Pacific and North Atlantic, the extratropical North America has weakened low-level continental low and upper-level ridge, hence a deficient summer rainfall. Corresponding to a high APO index, the African and South Asian monsoon regions are wet and cool, the East Asian monsoon region is wet and hot, and the extratropical North America is dry and hot. Wet and dry climates correspond to wet and dry soil conditions, respectively. The APO is also associated with significant variations of SST in the entire Pacific and the extratropical North Atlantic during boreal summer, which resembles the Interdecadal Pacific Oscillation in SST. Of note is that the Pacific SST anomalies are not present throughout the year, rather, mainly occur in late spring, peak at late summer, and are nearly absent during boreal winter. The season-dependent APO-SST relationship and the origin of the APO remain elusive. [ABSTRACT FROM AUTHOR]