Water stress is a situation where the availability of water is major constraint on human activity (Figure 1). There are many definitions but the tables here are based on the availability of water of less than 1000 m3/capita/year. The figures are based on projections for four different scenarios defined by the IPCC Special Report on Emissions Scenarios:

  • A1: Rapid growth, market led, convergence between regions, rapid technological change. This scenario has different variants. The one used here was A1F1 which is fossil fuel intensive. This gives a projected temperature increase of 4.5 ºC by 2100
  • B1: Same population growth as A1 but a much more environmentally sustainable development pathway. This gives a projected temperature increase of 2 ºC by 2100
  • A2: Relative to A1, less growth, more heterogeneous, higher population growth. This gives a projected temperature increase of 3.8 ºC by 2100
  • B2: Population growth less than A2, but higher than A1 and B1, environmentally sustainable development. This gives a projected temperature increase of 2.6 ºC by 2100
The following table is based on Arnell (Climate change and global water resources: SRES emissions and socio-economic scenarios, Global Environmental Change 14 (2004) 31–52). ) The values for water stress in the absence of climate change, effectively due to population increase, were reproduced from Table 14 of this publication. That table uses results from one model (HadCM3).

Download Publication by Arnell et. al.

Numbers of people (millions) with an increase and decrease in water stress: ‘‘drought runoff’’ used as indicator of resources: HadCM3 scenarios only
A1 A2 B1 B2
Increase in Stress
2025 1474 1026–2023 763 816–1234
2055 152 2102–2629 1491 1483–1698
2085 1787 3837–4295 1530 1708–2057
Decrease in Stress
2025 957 448–2211 1967 1903–2210
2055 2928 3360–4788 2700 2758–3314
2085 2354 5130–5902 2198 3117–3707
Water-stressed watersheds have drought runoff less than 1000 m3 / capita/year
As can be seen for most scenarios and time horizons the number of people moving out of water stress exceeds the number moving into it. It is projected that by the end of the century up to 1 billion people will have more water rather than less. Nigel Arnell was an IPCC lead author and the above reference is quoted in IPCC report ar4-wg2-chapter3.pdf.

Rapid impact-analysis tool

We have recently developed a tool for rapid analysis of the impacts of climate change - HYSIM-CC. It operates as follows:

  • Define the geographical area of interest
  • Download projections of precipitation and temperature for one of more scenarios, including the 20th century simulations for reference, and for a group of models
  • Select your area of concern: (i) River runoff and water resources. For this you will have to define the parameters of a very simple rainfall/runoff model. The model will take account of not only of changes to rainfall and evaporation but also to snowmelt runoff; (ii) Groundwater recharge and aquifer storage. This will use the same simple model as above; (iii) Irrigation. For this you will have to define the cropping period and field capacity
  • Run the program
The output from the program will provide an analysis of the changes in the parameters of interest for different time horizons:

  • For river flow and water resources it will identify the changes in mean annual flow and in the monthly distribution
  • For groundwater it will identify recharge rates and long term changes in aquifer storage
  • For irrigation it will identify and changes in crop water requirements