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 taken from Table 5 of this publication. The values for people moving into or out or water stress were taken from Table 9. That table sometimes uses results from one model, sometimes from several models. Where multiple models were used we took an average ignoring the ones which gave the highest and lowest values.
The Number of People (Millions) with Water Stress
|
A1 |
1368 |
2882 |
3400 |
2860 |
|
Become stressed |
|
126 |
280 |
380 |
|
Stop being stressed |
|
71 |
1168 |
1573 |
|
Stressed |
|
2937 |
2512 |
1667 |
|
B1 |
1368 |
2882 |
3400 |
2859 |
|
Become stressed |
|
123 |
261 |
235 |
|
Stop being stressed |
|
637 |
907 |
870 |
|
Stressed |
|
2368 |
2754 |
2224 |
|
A2 |
1368 |
3320 |
5596 |
8065 |
|
Become stressed |
|
147 |
358 |
605 |
|
Stop being stressed |
|
664 |
742 |
1666 |
|
Stressed |
|
2803 |
5212 |
7004 |
|
B2 |
1368 |
2883 |
3988 |
4530 |
|
Become stressed |
|
153 |
153 |
314 |
|
Stop being stressed |
|
656 |
940 |
913 |
|
Stressed |
|
2380 |
3201 |
3931 |
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 toolWe are currently developing a tool for rapid analysis of the impacts of climate change. It will operate 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 be 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
We are preparing a paper for publication on this methodology. An abstract will shortly appear on this site. The full model will be available for download by November 2009 at:
