Main findings

Water management in agriculture is a story of intensifying competition. Growing cities and industrialization demand relatively low volumes of high quality water but are able to add much more economic value per cubic metre of withdrawn water.

Today, agricultural uses more than 70 percent of all water withdrawals, but must to adapt to a future in which water will be reallocated to other users. In addition, hydro-environmental limits are being reached through continued withdrawals from watercourses, lakes and aquifers in key grain producing areas such as the Mediterranean basin, the Punjab, peninsular India and the North China Plain. Non-renewable groundwater in these regions is depleted as a result of agricultural withdrawals. In addition, the return flows of degraded water from agriculture is leading to salinization, eutrophication and the accumulation of pollutants.

The effects of additional climate drivers that will be superimposed upon natural resource systems and their management cannot be predicted with high certainty. There are clear differences in the statistical variability of climate and hydrology among continents (Peel, et al., 2001) that are not, as yet, well modelled by GCMs. Although there is only limited literature available on the prospective impacts of climate change on water balance and implications for irrigation, the impacts of these drivers are likely to include the following:

• reduction in crop yield and agricultural productivity where temperature constrains crop development (changes in diurnal fluctuation are as important as overall trends);


• reduced availability of water in regions affected by reduction in total precipitation (including Southern Africa and the Mediterranean Region);


• exacerbation of climate variability in places where it is already highest (Peel, et al., 2004 and 2004b);


• reduced storage of precipitation as snow and earlier melting of winter snow, leading to shifts in peak runoff away from the summer season when demand is high (Barnett, et al., 2005);


• inundation and increased damage in low-lying coastal areas affected by sea-level rise, with storm surges and increased saline intrusion into vulnerable freshwater aquifers;


• increased overall evaporative demand from crops as a result of higher temperatures;


• further depletion of non-renewable groundwater resources.

These climate-driven pressures are on top of other existing drivers adversely affecting water availability for agriculture and it is expected that climate change will intensify competition.

Reconciling this competition will be the main water management challenge and agriculture will have to address the challenge much more progressively. Allocations to cities, industry, rural water supply and sanitation are unlikely to be materially affected by climate change but, collectively, they will reduce the quantity of water that can be allocated to agricultural use and hydro-environmental services.

Short term recommendations - until 2030

investment plans and operational adjustments will need to be prepared
to address national and sub-regional and regional issues. These plans and adjustments will
comprise:

• monitoring the relative contribution of rainfed and irrigated production to global food balances to determine the long-term sensitivity of food production systems to climate change;


• elaborating vulnerability mapping such as the joint FAO/IIASA initiative that includes the Food Insecurity, Poverty and Environmental Global GIS database;


• determining the operational room to manoeuvre across river basin systems on the basis of updated assessments of the partition between surface and groundwater sources of supply, with the aim to improve the data for carrying out meaningful sensitivity analyses;


• •building in as much operational flexibility as possible into local/irrigation-scheme-level water management strategies in anticipation of both increased demand and the need to adjust operational supply.

Medium term recommendations – until 2050

existing agricultural water management systems at national and basin
level need to be analysed with respect to the Fourth Assessment Report of IPCC (AR4). Specifically this will entail:

• large surface irrigation systems fed by glaciers and snow melt (most notably northern India and China);


• groundwater systems in arid and semi-arid areas, where rainfall will decrease and become more variable;


• upstream watersheds, where a combination of irrigated agriculture, rainfed agriculture, pasture and forestry is practised;


• large deltas, which may be partly submerged by sea-level rise, increasingly prone to flood and storm and cyclone damage or experience saline incursions and intrusion through surface and groundwater respectively;


• seasonal storage systems in the monsoon regions, where the proportion of storage yield will decline but peak flood flows are likely to increase;


• supplemental irrigation areas, where the consequences of irregular rainfall are mitigated by short-term interventions to capture and store more soil moisture or runoff.
  

FAO support to adaptive strategies

Upon request, FAO could assist member countries in understanding the implications of climate change on water resources and agriculture and in developing better regional and local projections of impacts in order to develop planned adaptive strategies, improve water governance and build specific capacity in water management. Additionally, FAO could engage in a number of high impact and strategically chosen pilot projects to improve institutional capacity for climate change adaptation. These would have to be well resourced, long term and have high level buy-in from the partner country.

Given the instrumental value of water to all economic sectors, agriculture cannot act alone. National water management actions will need to be focused at national level but supported by regional and international initiatives. Specific recommendations are given in the document “Options for Decision Makers.”