Impact of reservoirs on river discharge and irrigation water supply during the 20th century

Abstract

[1] This paper presents a quantitative estimation of the impact of reservoirs on discharge and irrigation water supply during the 20th century at global, continental, and river basin scale. Compared to a natural situation the combined effect of reservoir operation and irrigation extractions decreased mean annual discharge to oceans and significantly changed the timing of this discharge. For example, in Europe, May discharge decreased by 10%, while in February it increased by 8%. At the end of the 20th century, reservoir operations and irrigation extractions decreased annual global discharge by about 2.1% (930 km 3 yr À1 ). Simulation results show that reservoirs contribute significantly to irrigation water supply in many regions. Basins that rely heavily on reservoir water are the Colorado and Columbia River basins in the United States and several large basins in India, China, and central Asia (e.g., in the Krishna and Huang He basins, reservoirs more than doubled surface water supply). Continents gaining the most are North America, Africa, and Asia, where reservoirs supplied 57, 22, and 360 km 3 yr À1 respectively between 1981 -2000, which is in all cases 40% more than the availability in the situation without reservoirs. Globally, the irrigation water supply from reservoirs increased from around 18 km 3 yr À1 (adding 5% to surface water supply) at the beginning of the 20th century to 460 km 3 yr À1 (adding almost 40% to surface water supply) at the end of the 20th century. The analysis is performed using a newly developed and validated reservoir operation scheme within a global-scale hydrology and vegetation model (LPJmL).

Accounting for environmental flow requirements in global water assessments

“…Since the beginning of the twentieth century, more than 800 000 dams have been built to facilitate increased withdrawals, and currently 75 % of the main rivers are fragmented (Biemans et al, 2011;Richter et al, 2003). Some large river basins, like the Yellow River basin, have seen their flow reduced by almost 75 % over 30 years due to increasing water withdrawals (Changming and Shifeng, 2002).…”

“…ture increase in food production will result in an increase in water demand (Biemans et al, 2011). As a result, about 60 % of the world's population could face surface water shortages from lakes, rivers, and reservoirs Rockström et al (2009).…”

The impact of climate change mitigation on water demand for energy and food: An integrated analysis based on the Shared Socioeconomic Pathways

“…This global database contains geographical locations for approximately 7000 dams, including information on maximum storage capacity. In grid cells where water storage facilities are provided by dams total annual blue water resources are available for irrigation (Biemans et al, 2011). In reality not all return flows are recoverable, due to inaccessibility or degradation, but LPJmL considers only the water outflow to oceans as non-recoverable (Jägermeyr et al, 2015).…”

Potential effects of climate change on inundation patterns in the Amazon Basin

“…Daily precipitation amount and distribution of wet days to calculate core processes such as photosynthesis, water fluxes and vegetation growth, are inferred using a stochastic method (Gerten et al, 2004). This method of using monthly inputs and recalculate them to quasi-daily values is used in most large-scale multiple-scenario studies (Alcamo et al, 2003;Biemans et al, 2011;Rost et al, 2008). Whether the treatment of climate data, with the present implementation of the weather generator in our model, significantly affects simulating results relative to the climate change signal is being investigated in an on-going study (Gerten et al, 2012).…”