On the variability and prediction of rainfall in the post-monsoon season over India

Considerable rainfall occurs in India during the post-monsoon period from October to December, particularly over north-eastern, eastern and southern regions, and this is of great significance in agricultural and allied sectors. For the first time, we have attempted to provide detailed information on the variability and predictability of the post-monsoon rainfall (PMR) of the country. Details on the summer monsoon rainfall from June to September are extensively documented. This study comprises four sections: (i) examination of large-scale rainfall features; (ii) examination of small-scale (or regional) rainfall features; (iii) diagnostic study in order to identify possible regional forcings and global teleconnections; and (iv) modelling long-period rainfall series and extrapolation of future trends for the next 10 years

Relationship between all-India summer monsoon rainfall and southern oscillation/eastern equatorial Pacific sea surface temperature

The interannual variability of all-India summer monsoon (June to September) rainfall and its teleconnections with the southern oscillation index (SOI) and sea surface temperature (SST) anomaly of the eastern equatorial Pacific ocean have been examined for the period 1871-1978 for different seasons (i.e., winter, spring, summer and autumn). The relationship (correlation coefficient) between all-India summer monsoon rainfall and SOI for different seasons is positive and highly significant. Further examination of 10-, 20- and 30-year sliding window lengths' correlations, brings out the highly consistent and significant character of the relationships. The relationship between all-India monsoon rainfall and SST for different seasons is negative and is significant at 1 level or above. Drought years are characterised by negative anomalies of SOI and positive anomalies of SST and vice versa with flood years. The relationship between SOI and SST is negative and significant at 0.1 level. The relationships between all-India summer monsoon rainfall, SOI and sst are expected to improve our understanding of the interannual variability of the summer monsoon

Western Indian Ocean marine and terrestrial records of climate variability: a review and new concepts on land-ocean interactions since AD 1660

We examine the relationship between three tropical and two subtropical western Indian Ocean coral oxygen isotope time series to surface air temperatures (SAT) and rainfall over India, tropical East Africa and southeast Africa. We review established relationships, provide new concepts with regard to distinct rainfall seasons, and mean annual temperatures. Tropical corals are coherent with SAT over western India and East Africa at interannual and multidecadal periodicities. The subtropical corals correlate with Southeast African SAT at periodicities of 16–30 years. The relationship between the coral records and land rainfall is more complex. Running correlations suggest varying strength of interannual teleconnections between the tropical coral oxygen isotope records and rainfall over equatorial East Africa. The relationship with rainfall over India changed in the 1970s. The subtropical oxygen isotope records are coherent with South African rainfall at interdecadal periodicities. Paleoclimatological reconstructions of land rainfall and SAT reveal that the inferred relationships generally hold during the last 350 years. Thus, the Indian Ocean corals prove invaluable for investigating land–ocean interactions during past centuries

2,000-year-long temperature and hydrology reconstructions from the Indo-Pacific warm pool

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 460 (2009): 1113-1116, doi:10.1038/nature08233.Northern Hemisphere surface temperature reconstructions suggest that the late twentieth century was warmer than any other time during the past 500 years and possibly any time during the past 1,300 years. These temperature reconstructions are based largely on terrestrial records from extra-tropical or highelevation sites; however, global average surface temperature changes closely follow those of the global tropics, which are 75% ocean. In particular, the tropical Indo- Pacific warm pool (IPWP) represents a major heat reservoir that both influences global atmospheric circulation and responds to remote northern latitude forcings. Here we present a decadally resolved continuous sea surface temperature (SST) reconstruction from the IPWP that spans the past two millennia and overlaps the instrumental record, enabling both a direct comparison of proxy data to the instrumental record and an evaluation of past changes in the context of twentieth century trends. Our record from the Makassar Strait, Indonesia, exhibits trends that are similar to a recent Northern Hemisphere temperature reconstruction. Reconstructed SST was, however, within error of modern values during the Medieval Warm Period from about AD 1000 to AD 1250, towards the end of the Medieval Warm Period. SSTs during the Little Ice Age (approximately ad 1550–1850) were variable, and 0.5 to 1°C colder than modern values during the coldest intervals. A companion reconstruction of δ18O of sea water—a sea surface salinity and hydrology indicator— indicates a tight coupling with the East Asian monsoon system and remote control of IPWP hydrology on centennial–millennial timescales, rather than a dominant influence from local SST variation.This work was financially supported by the US NSF and the Ocean Climate Change Institute of WHOI

On climatic fluctuations and environmental changes of the Indo-Gangetic Plains, India

Paralleling the Southern Himalayan Province, the Indo-GangeticPlains region (IGPR) of India (geographical area ∼ 6,00,000 km2) is veryimportant for the food security of South Asia. Due to numerous factors inoperation there is widespread apprehension regarding sustainability offragile ecosystems of the region. Literature provides detailed documentation of environmental changes due to different factors except climatic. The present study is intended to document the instrumental-period fluctuations of important climatic parameters like rainfall amounts (1829–1999), severe rainstorms (1880–1996) and temperature (1876–1997) exclusively for the IGPR. The summer monsoon rainfall over western IGPR shows increasing trend(170 mm/100-yr, significant at 1% level) from 1900 while over central IGPR it shows decreasing trend (5 mm/100-yr, not significant) from 1939 and over eastern IGPR decreasing trend (50 mm/100-yr, not significant) during 1900–1984 and insignificant increasing trend (480 mm/100-yr, not significant) during 1984–1999. Broadly it is inferred that there has been a westward shift in rainfall activities over the IGPR. Analysis suggests westward shift in the occurrence of severe rainstorms also. These spatial changes in rainfall activities are attributed to global warming and associated changes in the Indian summer monsoon circulation and the general atmosphericcirculation. The annual surface air temperature of the IGPR showed rising trend (0.53 ° C/100-yr, significant at 1% level) during 1875–1958 and decreasing trend (–0.93 ° C/100-yr, significant at 5% level) during 1958–1997. The post-1958 period cooling of the IGPR seems to be due to expansion and intensification of agricultural activities and spreading of irrigation network in the region. Lateral shift in the river courses is an environmental hazard of serious concern in the IGPR. In the present study it is suggested that meteorologic factors like strength and direction of low level winds and spatial shift in rainfall/climatic belt also play a significant role along with tectonic disturbances and local sedimentological adjustments in the vagrancy of the river courses over the IGP

Rainfall spatial variability and its impact on important environment processes in India

Desertification, River channel changes and rising trend in surface air temperature are environmental problems of serious concern in India. Elaborate analyses of spatial variation of annual, seasonal and monthly rainfall over the country have been carried out to understand the role of spatial variability on important environmental processes. Spatial variation of annual rainfall expansion and contraction of by examining expansion and contraction of the moisture regions and that of seasonal and monthly rainfall from expansion and contraction of respective period dry and wet zones using highly quality-controlled rainfall data from 316 locations for the period 1871-2006. Impacts of rainfall spatial variability on important environmental problems are discussed

Optimization of the raingauges for a representative all-India and subdivisional rainfall series

An objective approach similar to the forward selection of independent variables in the multiple linear regression has been attempted to optimize the network of raingauges for the summer monsoon rainfall (June-September total) series (1871-1984) of India as well as its 29 selected meteorological subdivisions prepared involving the data of 306 raingauges. For the all-India monsoon rainfall series twenty seven gauges entered the selection whose mean showed the correlation coefficient (CC) of 0.9869. Keeping in view the difficulties of getting data from all the 306 gauges, 35 India Meteorological Department (IMD) gauges with mean showing CC of 0.9898 have been identified for updating this series. The constructed all-India monsoon rainfall series for the period 1871-1992 using 35 selected observations is presented. It was interesting to note that the set of 35 gauges selected for the monsoon total has shown equally promising results for the all-India monsoon monthly (June-September) as well as the annual rainfall series. For the 29 subdivisional monsoon rainfall series, however, in total 188 IMD-gauges (62 of the total of 306 gauges) entered the selection. For 17 subdivisions the CC exceeded 0.98, for 3 subdivisions it varied between 0.97 and 0.98, for 5 subdivisions between 0.96 and 0.97 and for the remaining 4 subdivisions between 0.90 and 0.94. They showed equally encouraging results for the monsoon monthly and annual rainfall series for the different subdivisions. Limitations and implications of the optimization technique are also briefly discussed