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1.2. Crop forecasting philosophy of FAO, an overview.
FAO GIEWS website, René Gommes, Peter Hoefsloot Food Early Warning Systems
The incidence of drought-induced famine in many countries continues to be a global concern. Even in a good year, farmers in some pockets of a country may incur devastating crop losses. In times of civil strife or extensive floods, for example, some groups may experience a sharp reduction in their access to food supplies for reasons of physical exclusion from markets.
Many warning systems target both individual and institutional users, although the main target of warnings for food security is usually governments. In many developing countries, farmers still practice subsistence farming, i.e. they grow their own food, and depend directly on their own food production for their livelihood. Surpluses are usually small; they are mostly commercialised in urban areas (the urban population constitutes about 30% of the total population in Africa). Yields tend to be low: in Sahelian countries, for instance, the yields of the main staples (millet and sorghum) are usually in the range of 600 to 700 Kg/Ha during good years. Inter-annual fluctuations are such that the national food supply can be halved in bad years or drop to zero production in some areas. This is the general context in which food surveillance and monitoring systems were first established in 1978. Currently, about hundred countries on all continents operate food security warning systems; their name varies, but they are generally known as (Food) Early Warning Systems (EWS). They contribute to:
- informing national decision makers in advance of the magnitude of any impending food production deficit or surplus;
- improving the planning of food trade, marketing and distribution;
- establishing co-ordination mechanisms between relevant government agencies;
- reducing the risks and suffering associated with the poverty spiral.
EWS cover all aspects from food production to marketing, storage, national imports and exports down to consumption at the household level. Monitoring weather and estimating production have been essential components of the system from the onset, with an direct and active involvement of National Meteorological Services.
Over the years, the methodology has kept evolving, but crop monitoring and forecasting remain central activities:
- operational forecasts are now mostly based on readily available
- agrometeorological or satellite data, sometimes a combination of both. They do not depend on expensive and labour intensive ground surveys and are easily
revisable as new data become available;
- forecasts can be issued early and at regular intervals from the time of planting until harvest. As such, they constitute a more meaningful monitoring tool than the monitoring of environmental variables (e.g. rainfall monitoring);
- forecasts can often achieve a high spatial resolution, thus leading to an accurate estimation of areas and number of people affected.
Due to the large number of institutional and technical partners involved in EWS, interfacing between disciplines has been a crucial issue. For instance, crop prices are usually provided as farm gate or marketplace prices, food production and population statistics cover administrative units, weather data correspond to points (stations) not always representative for the agricultural areas, satellite information comes in pixels of varying sizes, etc. GIS techniques, including gridding, have contributed towards improving links in the “jungle” of methods and data.
The FAO Early Warning System
Established in the wake of the world food crisis of the early 1970s, the Global Information and Early Warning System (GIEWS) is the leading source of information on food production and food security for every country in the world, whether or not it is an FAO member. Over the years, a large inventory on global, regional, national and subnational food security has been maintained, refined and continuously updated.
GIEWS country monitoring concentrates on a group of some 80 “Low-Income Food-Deficit Countries. These countries are often particularly vulnerable to supply fluctuations caused, for instance, by crop failure or high international cereal prices.
National and local food policymakers need to know what is happening to export prices, global production, trade, stocks and demand. Regular reporting on world food situation and outlook is part of the service offered by GIEWS.
The main focus of the analysis is on cereals as information on other types of food is often extremely weak. However, the system is expanding its coverage of non-cereal staple foods particularly in countries where they constitute a large part of the national diet.
Early Warning Indicators and Convergence of Evidence.
The System collects information on possible “indicators” of food crisis such as local market food supplies, retail price rises and evidence of individual and community responses to food insecurity.
GIEWS strives for objectivity and consistency but the extremely complex nature of food security and humanitarian analysis makes a strict application of single indicator thresholds both impractical and technically questionable in their application to a wide array of situations. GIEWS, rather, supports methodology based on convergence of evidence from multiple sources (not limited to single assessment findings) as evaluated by analysts. In this manner, the analysts use the reference outcomes as a guide, but ultimately make a classification statement based on the convergence of evidence from all available sources. This evidence-based approach is not only practical and accommodating to a wide array of situations, it also focuses the burden of proof on the analysts, who need to demonstrate to all stakeholders (as if in a court of law) the validity and relevance of evidence in support of a classification statement, even if that statement is based on considerable ‘own best judgment’. Such a process enables accountability and accessibility for critique
End-Users of Early Warning information
The end-users of Early Warning information are government officials, policy makers, international bodies, aid agencies etc. Therefore rapid and effective communications are a key component of the System. Recent advances in computer technology and the Internet have enabled GIEWS to improve the timeliness of producing and disseminating reports. GIEWS’ core publications are “Food Outlook”, “Foodcrops and Shortages” and “Food Supply Situation and Crop Prospects in Sub-Saharan Africa”. Numerous Special Alerts and Special Reports are also produced. GIEWS’ publications are freely available to all institutions and individuals and are posted on the Internet at www.fao.org.
Unfortunately having an effective early warning system is no guarantee that interventions will follow. Famine, starvation and malnutrition continue to haunt many parts of the world. Food resources are not always mobilized in sufficient volume, or they arrive too late to save lives. War or civil strife often hamper logistic operations so much that relief programmes fail to reach the most needy. However, objective information and early warning continue to have a crucial role in ensuring that timely and appropriate action can be taken to avoid suffering.
Capacity building at a Regional an National level
The main priority for effective response to food crises remains the strengthening of national institutions for food security monitoring. FAO provides technical assistance to develop the capacity of government statistical services and specialized units or “Early Warning and Food Information Systems. These systems act as a focal point within governments for collecting, processing and communicating information on all the key variables that influence food security. This manual is part of this effort.
Crop monitoring and the FAO Water Balance Model
One of the main fundaments of any early warning system is crop forecasting. During the agricultural season crops are monitored and increasingly accurate forecasts for crop-specific yield are produced. At the core of crop forecasting the the FAO Water balance Model. This model forms the core of this manual and has been used for many years, especially by countries relying on rain-fed agriculture where inadequate availability of water to the crop is the main constraint. The model calculates a running water requirement satisfaction index (WRSI) during the growing season of the crop. The final value of this index is correlated with crop yield level. The correlation will be high, if all other factors affecting crop yield are fairly constant from year to year. Historical data on rainfall and crop yield are required, to establish a regression relationship between Index and yield. Unfortunately such data is in practice often not available.
Constraints of the model:
- A fairly dense network of raingauges and reliable records is required, because of high spatial variability in rain distribution in many countries. However, satellite based data are improving every year and could partly substitute ground data.
- The model is not reliable in case of extreme weather conditions
- The effects of excessive rainfall can not easily be accommodated
- Water holding capacity of the soil is a key variable in the model, for which there is often insufficient information and the variability may be high from place to place
- The input in the model should in principle be effective rainfall rather than the recorded rainfall. Therefore runoff as a proportion of total rainfall should be taken into consideration. Runoff depends on average slope of farmland, soil conditions and farming practices and again there is little data available.
To summarize, the Water Balance method provides a very useful “early warning” indicator for yield reduction due to water stress. However, in most circumstances, it can not be expected to produce a reliable quantitative yield forecast. The method will be used together with other indicators.