Accurate calculation of the environmental radiation dose rate (D?) is an essential part of trapped charge dating methods, such as luminescence and electron spin resonance dating. Although the calculation of D? is not mathematically complex, the incorporation of multiple variables and the propagation of uncertainties can be challenging. The Dose Rate and Age Calculator (DRAC) is an open access, web-based program which enables rapid D? calculation for trapped charge dating applications. Users can select from recently published attenuation and conversion factors to make mathematically robust, reproducible D? calculations. Comparison of DRAC calculated D? values against the published D? determinations of 422 samples from 32 studies results in a reproducibility ratio of 1.01?0.05. It is anticipated that DRAC will facilitate easier inter-laboratory comparisons and will provide greater transparency for D? calculations. DRAC will be updated to reflect the latest advances in D? calculation and is freely accessible at www.aber.ac.uk/alrl/drac. The code for DRAC is available from github at https://github.com/DRAC-calculator/DRAC-calculator. ?Embargo until 31/03/2017preprintPeer reviewe

The collapse of the Bronze Age Harappan, one of the earliest urban civilizations, remains an enigma. Urbanism flourished in the western region of the Indo-Gangetic Plain for approximately 600 y, but since approximately 3,900 y ago, the total settled area and settlement sizes declined, many sites were abandoned, and a significant shift in site numbers and density towards the east is recorded. We report morphologic and chronologic evidence indicating that fluvial landscapes in Harappan territory became remarkably stable during the late Holocene as aridification intensified in the region after approximately 5,000 BP. Upstream on the alluvial plain, the large Himalayan rivers in Punjab stopped incising, while downstream, sedimentation slowed on the distinctive mega-fluvial ridge, which the Indus built in Sindh. This fluvial quiescence suggests a gradual decrease in flood intensity that probably stimulated intensive agriculture initially and encouraged urbanization around 4,500 BP. However, further decline in monsoon precipitation led to conditions adverse to both inundation-and rain-based farming. Contrary to earlier assumptions that a large glacier-fed Himalayan river, identified by some with the mythical Sarasvati, watered the Harappan heartland on the interfluve between the Indus and Ganges basins, we show that only monsoonal-fed rivers were active there during the Holocene. As the monsoon weakened, monsoonal rivers gradually dried or became seasonal, affecting habitability along their courses. Hydroclimatic stress increased the vulnerability of agricultural production supporting Harappan urbanism, leading to settlement downsizing, diversification of crops, and a drastic increase in settlements in the moister monsoon regions of the upper Punjab, Haryana, and Uttar Pradesh.Indus Valley | floods | droughts | climate change | archaeology T he Harappan or Indus Civilization (1-8) developed at the arid outer edge of the monsoonal rain belt (9, Fig. 1) and largely depended on river water for agriculture (10). The Harappans settled the Indus plain over a territory larger than the contemporary extent of Egypt and Mesopotamia combined (Figs. 2 and 3). Between the Indus and Ganges watersheds, a now largely defunct smaller drainage system, the Ghaggar-Hakra, was also heavily populated during Harappan times (4, 5). Controlled by the Indian monsoon and the melting of Himalayan snow and glaciers (2,11,12), the highly variable hydrologic regime, with recurring droughts and floods, must have been a critical concern for Harappans, as it is today for almost a billion people living on the Indo-Gangetic Plain in Pakistan, northern India, and Bangladesh. In such challenging environmental conditions, both the development and the decline of the Harappan remain equally puzzling (13). We investigate how climate change affected this civilization by focusing on fluvial morphodynamics, which constitutes a critical gap in our current understanding of the Harappan in the way it affects habitability and human settlement patterns near rivers in...

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The Harappan Culture, one of the oldest known urban civilizations, thrived on the northwest edge of the Thar Desert (India and Pakistan) between 3200 and 1900 BCE. Its demise has been linked to rapid weakening of the summer monsoon at this time, yet reorganization of rivers may also have played a role. We sampled subsurface channel sand bodies predating ca. 4.0 ka and used U-Pb dating of zircon sand grains to constrain their provenance through comparison with the established character of modern river sands. Samples from close to archaeological sites to the north of the desert show little affinity with the Ghaggar-Hakra, the presumed source of the channels. Instead, we see at least two groups of sediments, showing similarities both to the Beas River in the west and to the Yamuna and Sutlej Rivers in the east. The channels were active until after 4.5 ka and were covered by dunes before 1.4 ka, although loss of the Yamuna from the Indus likely occurred as early as 49 ka and no later than 10 ka. Capture of the Yamuna to the east and the Sutlej to the north rerouted water away from the area of the Harappan centers, but this change significantly predated their final collapse.Peer reviewe

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The Thar Desert dune system in north‐west India and eastern Pakistan provides a rich archive of past environmental, geomorphological and climatic change. Much of the knowledge about the timing of dune accumulation in the Thar stems from scattered and sporadic records, based on older luminescence dating protocols. If the Thar dune record is to be incorporated within a growing multiproxy framework of past climate and environmental dynamics, it is necessary to generate a systematic record of the timing of dunefield accumulation. From this, relationships to climate and other drivers of dune activity may then be better established. To this end, an intensive programme of field sampling and optically stimulated luminescence (OSL) dating was carried out from a dunefield in the east‐central Thar Desert. This study presents the first detailed Holocene dune accumulation history from the region, and sheds light on the development of the multi‐generational parabolic dune systems. In contrast to previously published work, we identify the importance of the Holocene and the last millennium as periods with a number of preserved accumulation phases. OSL ages suggest that accumulation was persistent during the early and mid‐Holocene (within 11.7‐5.5 ka), late Holocene (2‐1 ka), as well as two major phases in the last millennium (600 – 200 a and within the last 70 a). Potential drivers of dune mobility in the last century include a strong anthropogenic dimension. Rapid net accumulation is recorded in the last 70 years, with rates varying between 2 and 5 m/year, in an environment where agricultural pressures have increased dramatically with the advent of irrigation schemes expanding into dunefield areas. © 2019 John Wiley & Sons, Ltd.

Precession-forced change in insolation has driven de-intensification of the Asian Monsoon systems during the Holocene. Set against this backdrop of a weakening monsoon, Indus Civilisation populations occupied a number of urban settlements on the Ghaggar-Hakra plains during the mid-Holocene from 4.5 ka until they were abandoned by around 3.9 ka. Regional climatic variability has long been cited as a potential factor in the transformation of Indus society, however there remain substantial gaps in the chronological framework for regional climatic and environmental change at the northern margin of the Thar Desert. This makes establishing a link between climate, environment and society challenging. This paper presents 24 optically stimulated luminescence ages from a mixture of 11 fluvial and aeolian sedimentological sites on the Ghaggar-Hakra floodplain/interfluve, an area which was apparently densely populated during the Indus urban phase and subsequently. These ages identify fluvial deposition which mostly pre-dates 5 ka, although fluvial deposits are detected in the Ghaggar palaeochannel at 3.8 ka and 3.0 ka, post-dating the decline of urbanism. Aeolian accumulation phases occur around 9 ka, 6.5 ka, 2.8 ka and 1.7 ka. There is no clear link to a 4.2 ka abrupt climate event, nor is there a simple switch between dominant fluvial deposition and aeolian accumulation, and instead the OSL ages reported present a view of a highly dynamic geomorphic system during the Holocene. The decline of Indus urbanism was not spatially or temporally instantaneous, and this paper suggests that the same can be said for the geomorphic response of the northern Thar to regional climate change