Using a 50-year (1951-2000) gridded (1-degree) daily rainfall data set over the Indian land region, we study two main aspects of the Indian monsoon. The first aspect deals with the changing nature of the rainfall annual cycle. This, to our knowledge, is the first attempt at studying the changing behaviour of the Indian monsoon rainfall annual cycle in a systematic way. The annual cycle is defined as a combination of the first few Fourier harmonics of daily rainfall. We then identify five attributes of the annual cycle for each year and location (grid): (a) the day of maximum intensity (peak day); (b) maximum intensity (peak value); (c) beginning; (d) end; and (e) duration of the annual cycle. An extensive statistical analysis of these five attributes over the central Indian region (16.5 – 26.5N; 74.5 – 86.5E) shows that the probability distributions of all attributes, barring the peak value, show a significant change in the last 25 years (1976-2000) compared to the first 25 years (1951-1975). The second issue addressed in this thesis deals with the behaviour of the intraseasonal oscillations in flood and drought years. Previous studies on this issue have been limited to only specific flood or drought years. Our analysis confirms earlier findings such as the northwestward propagation of the 10-20 day ISO. However, we also find, for the first time, based on 9 flood and 9 drought years, that the 20-60 day has an eastward propagation during drought years and remains stationary in flood years. The analysis is primarily statistical in nature, and providing a physical explanation for some of our findings is beyond the scope of our work. Finally, it is worth noting here that without the long-term gridded data, it would have been difficult to assess coherent changes over a large region and long time-period.

The role of feedback between erosional unloading and tectonics controlling the development of the Himalaya is a matter of current debate. The distribution of precipitation is thought to control surface erosion, which in turn results in tectonic exhumation as an isostatic compensation process. Alternatively, subsurface structures can have significant influence in the evolution of this actively growing orogen. <br><br>Along the southern Himalayan front new 40Ar/39Ar white mica and apatite fission track (AFT) thermochronologic data provide the opportunity to determine the history of rock-uplift and exhumation paths along an approximately 120-km-wide NE-SW transect spanning the greater Sutlej region of the northwest Himalaya, India. 40Ar/39Ar data indicate, consistent with earlier studies that first the High Himalayan Crystalline, and subsequently the Lesser Himalayan Crystalline nappes were exhumed rapidly during Miocene time, while the deformation front propagated to the south. In contrast, new AFT data delineate synchronous exhumation of an elliptically shaped, NE-SW-oriented ~80 x 40 km region spanning both crystalline nappes during Pliocene-Quaternary time. The AFT ages correlate with elevation, but show within the resolution of the method no spatial relationship to preexisting major tectonic structures, such as the Main Central Thrust or the Southern Tibetan Fault System. Assuming constant exhumation rates and geothermal gradient, the rocks of two age vs. elevation transects were exhumed at ~1.4 &#177;0.2 and ~1.1 &#177;0.4 mm/a with an average cooling rate of ~50-60 &#176;C/Ma during Pliocene-Quaternary time. The locus of pronounced exhumation defined by the AFT data coincides with a region of enhanced precipitation, high discharge, and sediment flux rates under present conditions. We therefore hypothesize that the distribution of AFT cooling ages might reflect the efficiency of surface processes and fluvial erosion, and thus demonstrate the influence of erosion in localizing rock-uplift and exhumation along southern Himalayan front, rather than encompassing the entire orogen.<br><br>Despite a possible feedback between erosion and exhumation along the southern Himalayan front, we observe tectonically driven, crustal exhumation within the arid region behind the orographic barrier of the High Himalaya, which might be related to and driven by internal plateau forces. Several metamorphic-igneous gneiss dome complexes have been exhumed between the High Himalaya to the south and Indus-Tsangpo suture zone to the north since the onset of Indian-Eurasian collision ~50 Ma ago. Although the overall tectonic setting is characterized by convergence the exhumation of these domes is accommodated by extensional fault systems.<br><br>Along the Indian-Tibetan border the poorly described Leo Pargil metamorphic-igneous gneiss dome (31-34&#176;N/77-78&#176;E) is located within the Tethyan Himalaya. New field mapping, structural, and geochronologic data document that the western flank of the Leo Pargil dome was formed by extension along temporally linked normal fault systems. Motion on a major detachment system, referred to as the Leo Pargil detachment zone (LPDZ) has led to the juxtaposition of low-grade metamorphic, sedimentary rocks in the hanging wall and high-grade metamorphic gneisses in the footwall. However, the distribution of new 40Ar/39Ar white mica data indicate a regional cooling event during middle Miocene time. New apatite fission track (AFT) data demonstrate that subsequently more of the footwall was extruded along the LPDZ in a brittle stage between 10 and 2 Ma with a minimum displacement of ~9 km. Additionally, AFT-data indicate a regional accelerated cooling and exhumation episode starting at ~4 Ma. <br><br>Thus, tectonic processes can affect the entire orogenic system, while potential feedbacks between erosion and tectonics appear to be limited to the windward sides of an orogenic systems. / Welche Rolle Wechselwirkungen zwischen der Verteilung des Niederschlags, Erosion und Tektonik während der Entwicklung des Himalayas über geologische Zeiträume gespielt haben bzw. heute spielen, ist umstritten. Dabei ist von besonderem Interesse, ob Erosion ausschliesslich in Folge tiefkrustaler Hebungsprozesse entsteht und gesteuert wird, oder ob Regionen besonders effektiver Erosion, bedingt durch isostatische Kompensation, die Lokation tektonischer Deformation innerhalb aktiver Orogene beeinflussen können. <br><br>Entlang der südlichen Himalayafront ermöglichen neue thermochronologische 40Ar/39Ar-Hellglimmer- und Apatite-Spaltspur-Alter die Bestimmung der Exhumationspfade entlang eines 120-km-langen NE-SW-gerichteten Profils, dass quer durch die gesamte Sutlej-Region des nordwestlichen, indischen Himalayas verläuft. Dabei deuten die 40Ar/39Ar-Daten in übereinstimmung mit früheren Studien darauf hin, dass zuerst das Kristallin des Hohen Himalayas und anschliessend, südwärts propagierend, das Kristallin des Niederen Himalayas während des Miozäns exhumiert worden ist. Im Gegensatz dazu weisen die neuen Apatit-Spaltspur-Alter auf eine gleichmässige und zeitgleiche Exhumation beider kristallinen Decken entlang des Sutlejflusses. Dieser 80x40 km weite Bereich formt einen elliptischen, nordost-südwest orientierten Sektor erhöhter Exhumationsraten während des Pliozäns und Quartärs. Innerhalb des Fehlerbereichs der Spaltspurmethode zeigen die Alter eine gute Korrelation mit der Höhe, zeigen aber gleichzeitig keine Abhängigkeit zu bedeutenden tektonischen Störungen, wie die "Main Central Thrust" oder dem "Southern Tibetan Fault System". Unter der vereinfachten Annahme konstanter Exhumationsraten deuten zwei verschiedene Höhenprofile auf Exhumationraten in der Grössenordnung von ~1,4 &#177;0,2 und ~1,1 &#177;0,4 mm/a bei einer durchschnittlichen Abkühlrate von ~50-60 &#176;C/m.y. während des Pliozäns bzw. Quartärs hin. Der anhand von Spaltspuraltern bestimmte Sektor verstärkter Exhumation korreliert mit dem Gebiet, das während des Holozäns hohen Niederschlags-, Erosion- bzw. Sedimenttransportraten ausgesetzt ist. Daher vermuten wir, dass die Verteilung von jungen Spaltspuraltern den regionalen Grad der Effiziens von Oberflächenprozessen und fluviatiler Erosion wiederspiegelt. Dies deutet auf einen Zusammenhang zwischen Erosion und der Lokalisierung von Hebung und Exhumation entlang der südlichen Front des Himalayas hin, und zeigt gleichzeitig, dass die Exhumation nicht einfach über die gesamte Front gleichmässig verteilt ist.<br><br>Trotz der Wechselwirkungen zwischen Exhumation und Erosion, die möglicherweise die Entwicklung der südlichen Himalayafront beeinflussen, beobachten wir auch tiefkrustale tektonische Exhumation in ariden Gebieten nördlich des Hohen Himalayas, die vermutlich im Zusammenhang mit plateauinternenen Deformationsprozessen steht. So haben sich zum Beispiel mehrere metaplutonische Gneissdomkomplexe zwischen dem Hohen Himalaya im Süden und der Indus-Tsangpo Suturzone im Norden seit der Indien-Asien Kollision vor ca. 50 Millionen Jahren entwickelt. Obwohl die Dome sich grossräumig in einem kommpressiven Spannungsfeld befinden, werden sie lokal entlang von Extensionsstrukturen exhumiert. Bis heute sind die Ursachen für die Entstehung dieser Prozesse umstritten.<br><br>Entlang der Indisch-Tibetischen Grenze erstreckt sich der fast vollkommen unbeschriebene Leo-Pargil-Gneissdomkomplex (31-34&#176;N/77-78&#176;E) innerhalb des Tethyschen Himalayas. Neue Geländekartierungen, strukturelle und geochronologische Daten der westliche Flanke des Leo Pargil Domes dokumentieren, dass dieser sich entlang zeitlich verbundener Abschiebungssysteme in einem extensionalen Regime entwickelt hat. Im Gelände wird der Dome von einem mächtigen Störungssystem begrenzt, die "Leo Pargil Detachment Zone" (LPDZ). Durch den tektonischen Versatz entlang der LPDZ liegen heute niedriggradig metamorphe Sedimentgesteine im Hangenden neben hochgradigen Gneisen in Liegenden. Unabhängig von der Probenlokation entlang des aufgeschlossenen Störungssystemes ergeben alle neuen 40Ar/39Ar-Hellglimmeralter um die 15 Ma und deuten auf ein regional wichtiges Abkühlungsereignis hin. Im Gegensatz dazu deuten die neuen Apatit-Spaltspuralter (AFT) auf eine kontinuierliche Exhumation der hochmetamorphen Einheiten im Liegenden der LPDZ unter sprödtektonischen Bedingungen zwischen 10 und 2 Ma hin, bei einem minimalen Versatz von ungefähr 9 km. Desweiteren deuten die Apatit-Spaltspur-Daten auf überregionale beschleunigte Abkülhlungs- bzw Exhumationsphase seit 4 Ma.<br><br>Daraus kann gefolgert werden, dass die tektonischen Prozesse die Entwicklung des gesamten Gebirges beflussen können, während potenzielle Wechselwirkungen zwischen Erosion und Tektonik auf die luvwärtigen Gebirgsflanken beschränkt zu bleiben scheinen.

Several previous studies have found that various characteristics of the Indian monsoon rainfall have shown secular changes over the past century. In this study, using a gridded (1degree) daily rainfall dataset, we analyse the spatio-temporal characteristics of the intensity and duration of monsoon (June through September) rainfall for secular changes over the last 50 years. The characteristics of the duration of rain events are described by wet and dry spells. A wet/dry spell is defined as a period of consecutive days with rainfall above/below a particular threshold. We choose to use a threshold that is a function of the local climatological mean, given the spatial heterogeneity of mean monsoon rainfall. The wet and dry spells are then divided into three categories: short [1 to 7 days], moderate [8 to 10 days], long [11 and more days] and analysed for changes over the past 50 years [19512000]. We find that while the number of short duration wet spells show a significant increase over the last 50 years (~15% change), the number of long duration wet spells show a significant decrease (~25%). Furthermore, while the numbers of short duration dry periods have shown a significant increase, the moderate and long duration dry spells do not shown an appreciable change. This increase and decrease in the short and long duration wet spells offset each other and consequently the total number of rainy days during the season has not shown any significant change over the past 50 years. In addition to the duration of wet and dry spells, we also analysed for changes in the accumulated rainfall of the short, medium and long duration wet spells. Our analysis suggests that while the depth of accumulated rainfall in short duration wet spells has shown a significant increase (~20%), the depth of rain in the long duration spells has shown a significant decrease (~30%) in the past fifty years.

Interannual variation of Indian summer (June-September: JJAS) monsoon rainfall (ISMR) depends on its relative intensity during early (June-July: JJ; contribution 52%) and late (August-September: AS; contribution 49%) phases. Apart from variations in sea surface temperature (SST), the primary reasons behind the variability during JJ and AS can be very different due to change in climatic conditions on account of post-onset processes. Here, using a high resolution general circulation model with seasonally varying climatological SST, mechanisms those govern the intensity of rainfall during JJ and AS are investigated. There is no significant relation-ship between intensity of precipitation over Indian region in JJ and AS. Moreover, the factors determining early monsoon (JJ) precipitation are different than that for late monsoon (AS). In absence of interannual SST variation, pre-monsoon soil moisture do not play a significant role for the interannual variation of monsoon precipitation over India. A large scale oscillation of the ITCZ is noticed on interannual time scale spanning from around 60◦E to 150◦E that brings spatially coherent flood and drought over this region. Early monsoon precipitation has a larger dependency on spring snow depth over Eurasia and phase of the upper tropospheric Rossby wave in May. However, late monsoon precipitation over India is mainly governed by the intensity and time scale of the intraseasonally varying convective cloud bands. This study suggests that early monsoon (JJ) precipitation over Indian region is more correlated with pre-monsoon signatures of land-atmosphere parameters. However, in later parts after the onset (AS), the monsoon intensity is primarily driven by its internal dynamics and characteristics of intraseasonal oscillation.

In the recent scenario of climate change, the natural variability and uncertainty associated with the hydrologic variables is of great concern to the community. This thesis opens up a new area of multi-disciplinary research. It is a promising field of research in hydrology and water resources that uses the information from the field of atmospheric science. A new way to identify and capture the variability and uncertainty associated with the hydrologic variables is established through this thesis. Assessment of hydroclimatic teleconnection for Indian subcontinent and its use in basin-scale hydrologic time series analysis and forecasting is the broad aim of this PhD thesis. The initial part of the thesis is devoted to investigate and establish the dependence of Indian summer monsoon rainfall (ISMR) on large-scale Oceanic-atmospheric circulation phenomena from tropical Pacific Ocean and Indian Ocean regions. El Niño-Southern Oscillation (ENSO) is the well established coupled Ocean-atmosphere mode of tropical Pacific Ocean whereas Indian Ocean Dipole (IOD) mode is the recently identified coupled Ocean-atmosphere mode of tropical Indian Ocean. Equatorial Indian Ocean Oscillation (EQUINOO) is known as the atmospheric component of IOD mode. The potential of ENSO and EQUINOO for predicting ISMR is investigated by Bayesian dynamic linear model (BDLM). A major advantage of this method is that, it is able to capture the dynamic nature of the cause-effect relationship between large-scale circulation information and hydrologic variables, which is quite expected in the climate change scenario. Another new method, proposed to capture the dependence between the teleconnected hydroclimatic variables is based on the theory of copula, which itself is quite new to the field of hydrology. The dependence of ISMR on ENSO and EQUINOO is captured and investigated for its potential use to predict the monthly variation of ISMR using the proposed method. The association of monthly variation of ISMR with the combined information of ENSO and EQUINOO, denoted by monthly composite index (MCI), is also investigated and established. The spatial variability of such association is also investigated. It is observed that MCI is significantly associated with monthly rainfall variation all over India, except over North-East (NE) India, where it is poor. Having established the hydroclimatic teleconnection at a comparatively larger scale, the hydroclimatic teleconnection for basin-scale hydrologic variables is then investigated and established. The association of large-scale atmospheric circulation with inflow during monsoon season into Hirakud reservoir, located in the state of Orissa in India, has been investigated. The strong predictive potential of the composite index of ENSO and EQUINOO is established for extreme inflow conditions. So the methodology of inflow prediction using the information of hydroclimatic teleconnection would be very suitable even for ungauged or poorly gauged watersheds as this approach does not use any information about the rainfall in the catchment. Recognizing the basin-scale hydroclimatic association with both ENSO and EQUINOO at seasonal scale, the information of hydroclimatic teleconnection is used for streamflow forecasting for the Mahanadi River basin in the state of Orissa, India, both at seasonal and monthly scale. It is established that the basin-scale streamflow is influenced by the large-scale atmospheric circulation phenomena. Information of streamflow from previous month(s) alone, as used in most of the traditional modeling approaches, is shown to be inadequate. It is successfully established that incorporation of large-scale atmospheric circulation information significantly improves the performance of prediction at monthly scale. Again, the prevailing conditions/characteristics of watershed are also important. Thus, consideration of both the information of previous streamflow and large-scale atmospheric circulations are important for basin-scale streamflow prediction at monthly time-scale. Adopting the developed approach of using the information of hydroclimatic teleconnection, hydrologic variables can be predicted with better accuracy which will be a very useful input for better management of water resources.

The thesis presents observations on the CO2 mixing ratio and the carbon isotopic ratio (13C/12C i.e. δ13) of atmospheric CO2 from the Indian region, for the period 2008 - 2011. An experimental system was established at the Centre for Earth Sciences, Indian Institute of Science, Bangalore. The experimental protocol involves collection of air samples, extraction of CO2 from the air samples collected, and finally the measurement of the CO2 mixing ratio and isotopic ratios of the extracted CO2 using pressure gauge readings and the dual inlet peripheral of the isotope ratio mass spectrometer, IRMS MAT 253. The isotopic ratios measured are scaled to VPDB and corrected for their N2O contribution. The experimental set up is calibrated with primary carbonate standards (NBS19) and an air CO2 reference mixture. The analytical precision (reproducibility of paired samples) obtained for the atmospheric CO2 measurement is ±7 µ mol.mol-1, ±0.05‰ and ±0.17‰ for the mixing ratio, δ 13C and δ 18Oof atmospheric CO2 respectively. The present study lays emphasis on the CO2 mixing ratio and the δ 13C of atmospheric CO2. There are very few atmospheric CO2 monitoring stations in India. There exists only one long-term monitoring station, Cabo de Rama, on the west coast of India. Of late, a few new stations for measuring atmospheric trace gases have been in operation, with the major focus being on remote locations. Urban stations in India have never been monitored before for both the mixing ratio and the δ13C of atmospheric CO2 together. Monitoring urban stations in India is crucial today as they have become prime emitters of CO2 due to industrial activity. The emission from the sources varies seasonally and is influenced by factors like the Indian monsoon. The Indian subcontinent is surrounded by the Arabian Sea, the Indian Ocean and the Bay of Bengal which act differentially in terms of CO2 uptake or release. There is also a differential transport of CO2 to and from the open ocean. Thus, understanding the spatial pattern of CO2 in the marine region close to the Indian subcontinent is essential to understand the oceanic uptake/release of CO2. As part of this thesis, an urban area was monitored during 2008 - 2011 and the marine region was observed during the southwest monsoon of 2009. The temporal variation of the CO2 mixing ratio and δ13C of atmospheric CO2 was observed over an urban station, Bangalore (12° 58′ N, 77° 38′ E, masl= 920 m), India. Since Bangalore is one of the developing urban cities in India, it is interesting to monitor Bangalore air to understand the impact of anthropogenic emissions on atmospheric CO2 variability. The region has four distinct seasons, dry summer (March – May), southwest monsoon (June – September), post monsoon (October – November) and winter (December – February). Thus, it is also an ideal location to identify the effect of different seasons on the contribution of CO2 from various sources. Air samples were collected from the Indian Institute of Science campus, Bangalore, during 2008 - 2011. Both the diurnal and seasonal variations of the mixing ratio and δ13C of CO2 were observed in Bangalore. On the diurnal scale, a higher mixing ratio with lighter carbon isotopes (negative value) of δ13C of CO2 was recorded in the air-CO2 analyzed during the early morning compared to the late afternoon samples. The observations suggest that coal combustion, biomass burning and car exhausts are possible sources for CO2 identified based on the Keeling plot method. The nocturnal boundary layer (NBL) is found to influence the buildup of CO2 concentration in the early morning. The presence of the NBL in the early morning prevents the mixing of locally produced air with the CO2 from the free atmosphere above. Thus, the free air contribution of CO2 is reduced during the early morning rather than in the afternoon. The effect of seasonal variability in the height of the NBL on the air CO2 mixing ratio and the 13C of atmospheric CO2 were documented in the present study. On a seasonal scale, the free air contribution of CO2 was found to be higher during the southwest monsoon and winter compared to the dry hot summer and post monsoon period. On a seasonal time scale, a sinusoidal pattern in both the mixing ratio and δ13C has been recorded in the observations. While compared with nearby CO2 monitoring stations like the coastal station, Cabo de Rama, and the Open Ocean station, Seychelles, maintained by CSIRO Australia and NOAA-CMDL respectively, Bangalore recorded higher amplitudes of seasonal variation. Seasonal scale variations have revealed an additional source i.e. emission from the cement industry along with other sources identified from diurnal variations. The emission of CO2 from these different sources is not constant; rather it was found to vary with different seasons. The enhanced biomass burning during the dry season drives the δ13C of atmospheric CO2 towards more negative values, while during the southwest monsoon; the increased biosphere cover pushes the δ13C value of atmospheric CO2 towards positive values. The effect of La Nina in 2011 is also prominent in the observation. The study also intends to identify the spatial variability of both the mixing ratio and δ 13C air-CO2 close to the urban station, Bangalore based on the simultaneous sampling of air from three locations, Bangalore and two coastal stations, Mangalore and Chennai, which are equidistant from Bangalore. Samples were collected during the southwest monsoon and winter of 2010 - 2011. The observations documented a similar source of CO2 for all the three stations irrespective of the season. The factor responsible for the variability in the mixing ratio and the δ 13C of air CO2 among these stations is the differential transport of air from the marine region and its mixing with locally produced air. To identify the variability of atmospheric CO2 over the marine region, the atmosphere over the Bay of Bengal was monitored during the southwest monsoon of 2009 as part of the Continental Tropical Convergence Zone (CTCZ) Cruise expedition. The ocean surface water was also monitored simultaneously for the δ18O of water and the δ13C of dissolved inorganic carbon measurement. The combined observations of both air and water have shown the transport of continental air to the marine region and its uptake by the ocean during the period. The variability of atmospheric-CO2 is also observed during special events like the solar eclipse. During the annular solar eclipse of 15th January, 2010 an unusually depleted source value was identified for Bangalore air. The role of the boundary layer and a change in photosynthesis were identified as possible factors affecting air CO2 composition. In conclusion, the thesis has provided the first observations on air CO2 variability from an urban station in India. The observations have identified the possible sources of CO2 and have demonstrated the role of climatic phenomena like the Atmospheric Boundary Layer, Indian Monsoon, and La Nina in controlling the behaviour of sources and sinks and thus affecting the air CO2 variability over land and ocean. The seasonal scale variation based on day-to-day variability in the afternoon samples has revealed the important contribution of emissions from the cement industry whose contribution was absent in the diurnal variability. Thus, it is evident from this study that the timing of air sampling is crucial while identifying the sources. The per capita emission of individual urban stations in India is different; thus, it is essential to monitor more urban stations to identify sources and their different contributions. In future, the simultaneous monitoring of both continental and marine air over both the Arabian Sea and the Bay of Bengal will enable us to understand the long range transport of atmospheric CO2. The long term monitoring of CO2 from the Indian region can give us a better perspective on the effect of the Indian monsoon on air CO2 variability and vice versa.