Small-scale farms’ contribution to food security and sustainable water use: The development of a 5 arcmin farm-size specific crop map of harvested area and its implication for water management

Su, H. (2021). Small-scale farms’ contribution to food security and sustainable water use: The development of a 5 arcmin farm-size specific crop map of harvested area and its implication for water management. IIASA YSSP Report. Laxenburg, Austria: IIASA

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Abstract

Small-scale farms play a critical role in current agricultural production and food security. Previous studies have developed various maps to estimate the geographical distribution of small-scale farms or the geographical distribution of crop production; however, current maps have limited capacities to support climate change and water resources studies where a grided farm size- and crop-specific map is needed. This study aimed to develop a 5 arcmin farm-size specific crop map of harvested area and to explore the implication for the management of water as a global resource. We developed such a map by downscaling a global database that directly measures the crop area and/or crop production per farm size for 42 crops and 56 countries. We downscaled the national data to grid-level by solving an optimization problem, where the objective function aimed to maximize the consistencies between the downscaled map and information from other databases on farm size structure, crop distribution, and field size distribution. We validated the developed map with empirical data from satellite images for oil palm, expert knowledge for coffee in Costa Rica, household surveys on irrigation, and similar estimated maps. Validations show an overall acceptable error. We then estimated small-scale farms’ contribution to total agricultural water consumption (blue and green water) using the output of the Global Crop Water Model (GCWM). Results show, under the 2 ha threshold, small-scale farms contribute to 25.8% of total agricultural water consumption globally, and this number is significantly higher in developing countries. Their contribution is also higher in labor-intensive crops (e.g. sweet potato, banana, rice, coconut) and domestic market-oriented crops. This means that the water consumed by small-scale farms may not be virtually exported to other countries. Future work will focus on map development (further validation, inclusion of more countries, estimation of crop production) and the assessment of water use sustainability, productivity (per net weight and per nutrient), and equity.

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