Back-casting global water stress: Reconstruction of past water demand and climate variability
Abstract
Water scarcity, caused by an existing regional imbalance of water availability and water demand, poses a serious environmental issue to the global society. Since the late 1990s, several studies have quantified blue water stress at the global scale by using the global hydrological models to simulate blue water availability (i.e., surface freshwater in rivers, lakes and reservoirs) which is confronted against water demand to compute water stress. While these assessments have identified regions suffering from current water stress and vulnerable to future water scarcity due to the effects of the climate change and prone to frequent droughts (e.g., Australia, Central and West USA, India, North-East China, Pakistan), the development of past water stress with the influences of population and economic growth and expanding irrigated area has not yet been quantified, which might give an important implication for the future assessment of water stress. Here, we developed a method to reconstruct past water demand from agricultural (i.e., irrigation and livestock), industrial and domestic (i.e., households and municipalities) sector over the period 1960 to 2001, which was used to contrast transient effects in its development against climate variability in the severity of water stress. Agricultural water demand was estimated based on past extents of irrigated area and livestock densities. We developed a simple algorithm to approximate the past economic development based on GDP, energy and household consumption and electricity production, which was subsequently used together with population numbers to estimate industrial and domestic water demand. Desalinated water use and groundwater abstraction were additionally calculated over the same period, the latter being proportional to water demand. Various annual country statistics were used but resulted estimates were gridded at a spatial resolution of 0.5° and disaggregated into a monthly temporal scale as it can be expected that availability of water is often out of phase with water demand and that actual water stress may be underestimated using yearly totals. Climate variability is expressed by monthly blue water availability simulated by the global hydrological model PCR-GLOBWB coupled with a prospective reservoir operation scheme at a spatial resolution of 0.5°. The comparisons of irrigation, industrial and domestic water demand between resulted estimates and reported values (e.g., FAO AQUASTAT) show generally good agreements from 1960 to 2000 (R2>0.95 and 0.9<α<1.1). We estimate that during this period the amount of global (gross/net) water demand was more than doubled from 1708/818 to 3708/1832 km3/yr while the number of people exposed to severe water stress (i.e., water scarcity index>0.4) tripled from 0.5 to 1.8 billion (17 to 30%) of the global population. Time series of country averaged water stress reveal that growing water demand enhanced the intensity of water stress up to 200% while climate variability is often a main determinant for extreme events (i.e., droughts). However, our results also suggest that in several countries (e.g., India, China, Mexico) some of the past observed droughts were anthropogenically driven due to increased water demand.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H51I..05W
- Keywords:
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- 1803 HYDROLOGY / Anthropogenic effects;
- 1807 HYDROLOGY / Climate impacts;
- 1812 HYDROLOGY / Drought;
- 1847 HYDROLOGY / Modeling