Water Resources

From The World Economic Forum

Water resource managers are concerned with water availability, accessibility, and potability. Changes to surface and groundwater levels are determined by the balance between water inflow and outflow, and impact assessments should be wary of uncertainties in precipitation projections and future human use patterns. Responses to climate change by other sectors can also indirectly affect the availability of potable water in a region. For example, changes in agricultural practices can lead to increased runoff, affecting water quality; impacts to the energy sector, such as increased frequency of electricity outages and disruption of fuel supply chains, can affect groundwater accessibility. Water resource managers are familiar with other impacts on the water supply, such as changes in human populations or the impacts of new industries on water use, and should consider how climate impacts on different sectors may affect water availability.

Water flows to an area are determined by precipitation and surface runoff, and below-ground movement of water from one location to another. Water flow paths are determined by surface topography and the structure and features below ground. In mountainous areas a substantial portion of rainfall is provided by orographic precipitation. In these areas, coarse-resolution GCMs may be inadequate to project future rainfall and therefore surface water availability. On the other hand, spatial precision may be less necessary when considering water supply over a large watershed, and so the type of data used may depend on the size of the geographic area of interest.

The best data for precipitation are derived from station measurements. However these provide little insight into future precipitation trends. Precipitation tends to show considerable spatial variability, so interpolated or reanalysis data should be used with caution, particularly over areas with sparse meteorological stations or variable topography. GCM simulations of precipitation also poorly replicate daily precipitation. Models tend to project more days with light rain, while observations typically show fewer rainy days with more intense precipitation. High rainfall intensity can increase surface runoff (and reduce soil moisture recharge), so local hydrologists should consider that GCM and RCM projections of rainfall likely underestimate the daily variability of precipitation and may overestimate soil moisture recharge.

Loss from a watershed is determined by evaporation rates, human usage, and outflow rates. Evaporation rates increase with higher temperatures and faster surface winds. However, they decrease with increased humidity. Temperatures in target countries are expected to increase over the next century. While humidity may also increase in some areas, an overall trend towards increased evaporation is expected. Accessibility and potability can also be affected by water storage patterns. Groundwater (water stored in aquifers below ground) can be more difficult to access than surface water (water stored in lakes or rivers). However, groundwater, which is filtered by layers of rock and soil, is also less susceptible to contamination.

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