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Accounting for over 70% of global water withdrawals, irrigation plays a crucial role in the development of agriculture. Irrigation water requirement ( WIRR ) will be influenced by climate change due to the alteration in soil water balances, evapotranspiration, physiology and phenology under global warming. This is particularly true for rice, a high water-consuming crop. Therefore, exploring the impact of climate change on rice WIRR is of great significance for the sustainable utilization of water resources and food security. This paper aims to investigate spatially and temporally the responses of rice WIRR to climate change in the middle and lower reaches of the Yangtze River (MLRYR), which is one of the most important rice farming districts in China. With the help of the specially developed rice growing period calculation method and water balance model coupled with rice irrigation scheduling, the impacts of climate change on WIRR for early rice, late rice and single cropping rice during the historical (1961–2012) and future (2011–2100) periods were evaluated. Meanwhile, to consider the uncertainty from climate models in future projection, four GCMs under RCP2.6, RCP4.5 and RCP8.5 emission scenarios from the 5th Coupled Model Intercomparison Project (CMIP5) were employed as the input of the water balance model. The results indicate the following: (1) The days of growing period ( DGP ) for all three types of rice display shortened trends in historical and most future periods. However, in the middle region of the MLRYR, the DGP for early rice and late rice would increase by up to10 days in 2080s under RCP8.5 scenario. (2) Over the past 50 years, the WIRR significantly decreased by 1.58 and 2.10 mm yr −1 for late rice and single cropping rice, respectively. While for early rice, the WIRR only slightly decreased by 0.13 mm yr −1 . (3) Projected future WIRR would increase for all three types of rice in the whole region under RCP4.5 and RCP8.5 scenarios (up to 100 mm), but decrease for single cropping and late rice in the southeast region (up to 40 mm). The results can provide beneficial reference and comprehensive information to understand the impact of climate change on the agricultural water balance and improve the regional strategy for water resource utilization and agricultural management in the middle and lower reaches of the Yangtze River. [ABSTRACT FROM AUTHOR]

Summary: The paper describes a set of modelling utilities (a root-zone model, a grid-distribution tool, and a modified Modflow-2000 model) that can be used to simulate the water cycle of a city in terms of root-zone water balance, water supply, wastewater, storm runoff, groundwater flow, streamflow, and the interactions between these subsystems. The utilities are used to simulate the water cycle in the Copenhagen area (976km2) during the period 1850–2003. Long-term time series of hydraulic head, streamflow, and inflow to sewage works have been used to manually calibrate the model parameters. We used a step-wise calibration strategy, using different parts of the data in the various steps, to calibrate hydrogeological parameters, storm runoff parameters, and parameters governing the interactions between groundwater and leaky pipe systems, respectively. Simulations indicate that present rates of groundwater leakage into streams, lakes, and wetlands constitute 60% of pre-urbanization levels due to massive groundwater extraction. However, the current problems of groundwater shortages and streamflow depletion would have been far worse, if precipitation had not increased by 20% since 1850. Model simulations indicate that urbanization has lowered current groundwater recharge due to the establishment of impervious areas and due to negligible contributions from leaky pipe systems. This is opposite to the reported general tendency of enhanced recharge due to urbanization. However, current recharge rates within Copenhagen are simulated to be 20% higher than prior to urbanization, which is attributed to the increase in precipitation during the study period. [ABSTRACT FROM AUTHOR]

Abstract: In the North China Plain (NCP), while irrigation using groundwater has maintained a high-level crop productivity of the wheat–maize double cropping systems, it has resulted in rapid depletion of groundwater table. For more efficient and sustainable utilization of the limited water resources, improved understanding of how crop productivity and water balance components respond to climate variations and irrigation is essential. This paper investigates such responses using a modelling approach. The farming systems model APSIM (Agricultural Production Systems Simulator) was first calibrated and validated using 3 years of experimental data. The validated model was then applied to simulate crop yield and field water balance of the wheat–maize rotation in the NCP. Simulated dryland crop yield ranged from 0 to 4.5tha−1 for wheat and 0 to 5.0tha−1 for maize. Increasing irrigation amount led to increased crop yield, but irrigation required to obtain maximum water productivity (WP) was much less than that required to obtain maximum crop yield. To meet crop water demand, a wide range of irrigation water supply would be needed due to the inter-annual climate variations. The range was simulated to be 140–420mm for wheat, and 0–170mm for maize. Such levels of irrigation applications could potentially lead to about 1.5myear−1 decline in groundwater table when other sources of groundwater recharge were not considered. To achieve maximum WP, one, two and three irrigations (i.e., 70, 150 and 200mmseason−1) were recommended for wheat in wet, medium and dry seasons, respectively. For maize, one irrigation and two irrigations (i.e., 60 and 110mmseason−1) were recommended in medium and dry seasons, while no irrigation was needed in wet season. [Copyright &y& Elsevier]

Abstract: In this paper we present a modelling study to investigate the impacts of climate change on the chloride concentration and salinisation processes in two man-made freshwater lakes in the Netherlands, Lake IJsselmeer and Lake Markermeer. We used a transient compartmental chloride and water balance model to elucidate the salinisation processes occurring under present conditions and assess future salinisation under two climate forcing scenarios. The model results showed that the Rhine River is the dominant determinant for the chloride concentration in both lakes, followed by drainage of brackish groundwater from the surrounding polders. The results further show that especially during dry years, seawater intrusion through the tidal closure dam is an important source of chloride to Lake IJsselmeer. The results from the climatic forcing scenarios show that Lake IJsselmeer is especially vulnerable to climate-induced salinisation whereas effects on Lake Markermeer are relatively small. Peak chloride concentrations at the raw water intake of the Andijk drinking water facility on Lake IJsselmeer are projected to increase to values above 250 mg/l in the most far-reaching climate change scenario W+ in 2050 for dry years. This is well above the maximum allowable concentration of 150 mg/l for chloride in drinking water. Modelling showed that climate change impacts the chloride concentrations in a variety of ways: 1) an increasing occurrence of low river flows from summer to autumn reduces the dilution of the chloride that is emitted to the Rhine with a constant load thereby increasing its concentration; 2) increased open water evaporation and reduced rainfall during summer periods and droughts increases the chloride concentration in the water; and 3) rises in sea level increase seawater intrusion through the tidal closure dam of Lake IJsselmeer. The processes described here are likely to affect many other tidal rivers or lakes and should be considered when planning future raw water intake stations for drinking water production or agricultural water supply. [Copyright &y& Elsevier]

• Increased precipitation and temperature are expected under 1.5/2.0 °C warming in Central Asia. • ETc is projected to increase in Central Asia under 1.5 °C and 2.0 °C global warming. • Water gap (precipitation-CWR) will widen for rainfed north Kazakhstan and irrigated Fergana. In the arid region of Central Asia, climate change leads not only to changes in water availability generated by glacier/snow melt in the alpine regions, but also to changes in water consumption. This paper evaluates agricultural water demand and water supply (represented by precipitation) for the five Central Asian countries (Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan) under global warming conditions of 1.5 °C and 2.0 °C. As Central Asia is more sensitive to climate change compared to the global average, the temperature is predicted to rise by 1.7 °C and 2.6 °C and precipitation to increase by 9 % and 12 % in global warming scenarios of 1.5 °C and 2.0 °C, respectively. The average crop water requirement (CWR) is expected to increase by 13 mm and 19 mm per year, respectively, under the global warming scenarios of 1.5 °C and 2.0 °C. A widening gap between water supply and water demand is expected compared to the historical period (1976–2005) under global warming scenario of 2.0 °C. Under global warming of 2.0 °C, the anticipated water gaps between precipitation and CWR are projected to increase by 2.8 × 108 m3 and 1.5 × 108 m3 for the rainfed north Kazakhstan region and the irrigated Fergana region while the increase of precipitation could able to meet the increase in CWR under global warming of 1.5 °C. Investigating the water balance for major planting areas in water-limited Central Asia could provide a scientific basis for sustainable development of the entire region. [ABSTRACT FROM AUTHOR]