across the full extent of the IGB. The aquifer system is usually represented as a single category on 66 hydrogeological maps [6]. However, in practice the system is complex and heterogeneous with large 67 spatial differences in permeability, storage, recharge and water chemistry as well as having an 68 important depth dimension. This complexity strongly influences how each part of the aquifer 69 responds to stresses [7]. The IGB is home to the largest surface water irrigation system in the world, 70 constructed during the 19 th and early 20th century to redistribute water from the Indus and Ganges 71 through a canal network >100,000 km long. Leakage from this irrigation infrastructure has had a 72 profound impact on the current quantity and quality of groundwater resources and is a significant 73 factor governing its response to contemporary and future pressures. Increasing groundwater use for 74 irrigation poses legitimate questions about the future sustainability of abstraction from the basin 75 and future groundwater security of this region is a major social-political concern [8]. 76Recent discussion of water security has been dominated by interpretations of remotely-sensed 77 gravity data from the GRACE mission gathered at a coarse scale of 400x400 km are poorly constrained by ground-based observations; local field studies nonetheless provide partial 82 insight into system dynamics. These include evidence of: declining groundwater levels [11,12,13], 83 groundwater security has been introduced by forecasts of climate change and the potential for 88 significant change to precipitation, river flows and groundwater recharge [20,21,22]. 89Here we present for the first time an analysis of the status of groundwater across the IGB alluvial 90 aquifer based entirely on in situ measurements. We use a statistical analysis of multiyear 91 groundwater-level records from 3652 water-wells and a compilation and interpretation of existing 92 high resolution spatial datasets and studies within Pakistan, India, Nepal and Bangladesh to assess: 93 (1) groundwater-level variations; (2) groundwater salinity; and (3) We find that the water-table within the IGB alluvial aquifer is typically shallow (< 5 m below ground 98 surface) and the long-term trend is relatively stable throughout much of the basin, with some 99 important exceptions. In areas of high groundwater abstraction in northwest India and the Punjab in 100 Pakistan ( Figure 2) the water-table can be >20 m bgl and in some locations is falling at rates of > 1 101 m/a (Figure 3). In areas of equivalent high irrigation abstraction within Bangladesh, the average 102 water-table remains shallow (<5 m bgl) due to greater direct recharge and high capacity for induced 103 recharge. Groundwater levels are deep and falling beneath many urban areas, and particularly in 104 large groundwater dependant cities such as Lahore, Dhaka and Delhi [23]. Shallow and rising water-105 tables are found in the Lower Indus, parts of the lower Bengal basin and in places throughout the 106 IGB aqui...

This paper attempts to characterize the physical and optical properties of the aerosols along with relevant meteorological parameters at a typical location in the Ganga basin. The emphasis is on delineating the prolonged foggy/hazy conditions, a phenomenon believed to be of relatively recent origin, faced by millions of people during the winter months of December and January. Collocated measurements of a number of aerosol and atmospheric parameters were made using ground‐based instruments as part of an intense field campaign launched under the Indian Space Research Organization Geosphere Biosphere Programme in December 2004. The meteorological conditions suggest limited mixing due to shallow boundary layer thickness and essentially calm wind conditions. Monthly mean aerosol optical depth was high (0.77 ± 0.3 at 0.5 μm wavelength) and showed high spectral variation (first‐order Ångström exponent for all wavelengths, α = 1.24 ± 0.24). The second‐order Ångström exponent α′ derived for 0.34, 0.5, and 1.02 μm wavelengths showed much higher curvature in the aerosol optical depth spectrum on the hazy/foggy days (0.93 ± 0.36) as compared to that during the clear days (0.59 ± 0.3). Single‐scattering albedo (0.87–0.97) showed strong spectral variation. Aerosol mass concentration was high with monthly average 125.9 ± 47.1 μg m−3. Fine mode particles (<1 μm) contributed ∼75% to the total mass of aerosols. Similarly, aerosol number concentration was found to vary in the range 1.5–2 × 103 cm−3, with fine mode particles contributing to ∼99.6%. The hazy/foggy conditions typically prevailed when higher daytime relative humidity, lower maximum temperature, and higher fine/accumulation mode particles were observed. The companion paper suggests that the rise in aerosol mass/number concentration could be attributed to the aqueous‐phase heterogeneous reactions mediated by anthropogenic pollutants and the associated reduction in boundary layer thickness and suppressed mixing.

The Indo-Gangetic aquifer is one of the world's most important transboundary water resources, and the most heavily exploited aquifer in the world. To better understand the aquifer system, typologies have been characterized for the aquifer, which integrate existing datasets across the IndoGangetic catchment basin at a transboundary scale for the first time, and provide an alternative conceptualization of this aquifer system. Traditionally considered and mapped as a single homogenous aquifer of comparable aquifer properties and groundwater resource at a transboundary scale, the typologies illuminate significant spatial differences in recharge, permeability, storage, and groundwater chemistry across the aquifer system at this transboundary scale. These changes are shown to be systematic, concurrent with large-scale changes in sedimentology of the Pleistocene and Holocene alluvial aquifer, climate, and recent irrigation practices. Seven typologies of the aquifer are presented, each having a distinct set of challenges and opportunities for groundwater development and a different resilience to abstraction and climate change. The seven typologies are: (1) the piedmont margin, (2) the Upper Indus and Upper-Mid Ganges, (3) the Lower Ganges and Mid Brahmaputra, (4) the fluvially influenced deltaic area of the Bengal Basin, (5) the Middle Indus and Upper Ganges, (6) the Lower Indus, and (7) the marine-influenced deltaic areas.

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