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Water use patterns were explored for three small communities that are located in proximity to agricultural fields and rely on their local wells for potable water supply. High-resolution water use data, collected over a four-year period, revealed significant temporal variability. Monthly, daily, and hourly water use patterns were well described by autoregressive moving average (ARMA) models. Model development was supported by unsupervised clustering analysis via self-organizing maps (SOMs) that revealed similarities of water use patterns and confirmed the time-series water use model attributes. The inclusion of ambient temperature and rainfall as model attributes improved ARMA model performance for daily and hourly water use from R2 ~0.86–0.87 to 0.94–0.97 and from R2 ~0.85–0.89 to 0.92–0.98, respectively. Water use predictions for an entire year forward in time was feasible demonstrating ARMA models’ performance of (i) R2 ~0.90–0.94 and average absolute relative error (AARE) of ~2.9–4.9% for daily water use, and (ii) R2 ~0.81–0.95 and AARE ~1.9–3.8% for hourly water use. The study suggests that ARMA modeling should be useful for analysis of temporally variable water use in support of water source management, as well as assessing capacity building for small water systems including water treatment needs and wastewater handling.

Canola has a high nitrogen requirement and optimal nitrogen (N) management in environments with variable rainfall is a challenge. This study investigated the impact of timing of N as a single or split application at different growth stages on seed yield, N uptake and water-use efficiency in canola. Nitrogen rates of 100 and 200 kg ha&minus, 1 were applied after sowing when two leaves were unfolded or equally split between the rosette, green bud and first flower stages. The experiments were conducted at two sites with contrasting rainfall and a supplementary irrigation treatment at the low rainfall site, generating a third environment. Nitrogen application increased seed yield by up to 20% at a high rainfall site and by up to 77% at a medium rainfall site, but the timing of N did not significantly affect the yield response to N. Seed yield was closely associated with total dry matter production and seed m&minus, 2. N-use efficiency was influenced more by N recovery and uptake efficiency, rather than physiological efficiency, which highlights the importance of soil moisture availability and the ability of the crop to exploit soil water and N reserves. The results suggest that better use of subsoil moisture by overcoming some of the subsoil constraints may be an avenue for further improvements in yield and nitrogen-use efficiency (NUE) of canola in this environment.

Water use patterns of understorey vegetation are species-dependent. Calluna vulgaris showed little or no regulation of transpiration in response to soil water depletion or air vapour pressure deficit, unlike Pteridium aquilinum, Rubus sp. and Molinia caerulea. Evapotranspiration at forest stand scale is the sum of three components: overstorey and understorey transpiration, and evaporation from soil. During periods of soil water shortage, evapotranspiration of trees declines significantly, but the response of understorey vegetation is less well known. Some reports suggest that understorey vegetation can sometimes be the main source of water depletion in a forest stand during drought episodes. We assessed transpiration in response to decreased soil water content (SWC) and increased vapour pressure deficit (VPD) in the atmosphere for four understorey species with contrasting patterns of resource capture. Potted plants of Pteridium aquilinum, Molinia caerulea, Calluna vulgaris and Rubus sect. Fruticosi were grown under two radiation levels combined with three levels of SWC. Temperature, radiation, VPD and transpiration were monitored. Calluna vulgaris displayed a water spender behaviour with little or no regulation of transpiration during soil water depletion and increased VPD, whereas Pteridium aquilinum showed a low transpiration rate whatever the conditions. Rubus sect. Fruticosi gradually decreased transpiration during soil water depletion and increased VPD, whereas Molinia caerulea responded strongly to soil water depletion but only moderately to VPD. This study highlights the importance of adding identity and water use strategy of understorey species to the tree canopy component to establish a reliable forest water balance.

This paper presents the first basin-wide assessment of the potential impact of climate change on the hydrology and production of the Ganges system, undertaken as part of the World Bank’s Ganges Strategic Basin Assessment. A series of modeling efforts, downscaling of climate projections, water balance calculations, hydrological simulation and economic optimization, inform the assessment. The authors find that projections of precipitation across the basin, obtained from 16 Intergovernmental Panel on Climate Change-recognized General Circulation Models are highly variable, and lead to considerable differences in predictions of mean flows in the main stem of the Ganges and its tributaries. Despite uncertainties in predicted future flows, they are not, however, outside the range of natural variability in this basin, except perhaps at the tributary or sub-catchment levels. The authors also find that the hydropower potential associated with a set of 23 large dams in Nepal remains high across climate models, largely because annual flow in the tributary rivers greatly exceeds the storage capacities of these projects even in dry scenarios. The additional storage and smoothing of flows provided by these infrastructures translates into enhanced water availability in the dry season, but the relative value of this water for the purposes of irrigation in the Gangetic plain, and for low flow augmentation to Bangladesh under climate change, is unclear.